The evolution of charcoal-burning suicide: A systematic scoping review

Abstract

Introduction:

Suicide by charcoal burning has accounted for more than 100,000 deaths. It has become an increasingly common suicide method in Hong Kong since first reported in 1998, and it has spread into South Korea, Taiwan, Japan and other countries. This systematic scoping review aimed to explore current evidence on trends, risk factors, impact of media and prevention strategies for this suicide method, and to identify research gaps.

Methods:

A search for articles published from January 1998 to June 2021 was conducted through electronic databases (MEDLINE, EMBASE, SCOPUS and PsycINFO) with the keywords (suicide*) AND (charcoal). Articles describing prevalence, trends, characteristics, risk factors and prevention strategies of charcoal burning suicide deaths were included. Non-peer-reviewed articles, non-English articles, commentaries/editorials/letters, poster abstracts, reviews, meta-analyses and studies that documented only charcoal burning suicide attempters/survivors were excluded.

Results:

Eighty-eight studies were identified, most from East Asia. Charcoal burning suicide rates in Hong Kong, Taiwan and Japan has passed the peak, while continuing to increase in South Korea. Risk factors are changing and not static. Media appears to play an important role in triggering and spreading information. Restricting access to charcoal, and raising public awareness have been effective in the short term in preventing charcoal burning suicide, but there is little information on their long-term effectiveness or sustainability.

Discussion:

More research is required to update the development and dynamic changes of charcoal burning suicide and the contributing factors. The evidence from this review may assist in detecting and intervening early for future novel suicide methods.

Keywords

Suicide charcoal burning suicide prevention mental health systematic scoping review

Introduction

Suicide has been identified as a serious global public health issue, accounting for 700,000 lives annually (World Health Organization, 2021). The emergence of new suicide methods such as charcoal burning, have led to a significant increase in suicide rates (Thomas et al., 2011). Death occurs from carbon monoxide poisoning by inhaling burning barbecue charcoal gases in enclosed spaces. The first publicly documented case of suicide by charcoal burning occurred in 1998 in Hong Kong (Chan et al., 2005). It was widely reported by print and electronic media, with photos from the scene and detailed descriptions of this suicide method, and soon became one of the most common suicide methods in Hong Kong (Men et al., 2021; Yip and Lee, 2007). It also spread quickly to nearby regions such as Taiwan, Japan and South Korea (Chang et al., 2014). Charcoal burning suicides are now epidemic in many East Asian communities. However, few suicides by charcoal burning appear to have been documented outside Asia (Chen et al., 2009b). It is estimated that since 1998, over 100,000 cases of suicide deaths in East Asia can be attributed to charcoal burning (Centre for Suicide Research and Prevention, 2022; Ministry of Health and Welfare, 2021; World Health Organization, 2022). Charcoal burning has developed from a new suicide method to a common one throughout the 23-year evolution in Asian communities. It provides a unique opportunity to understand how this method spread, in particular the local and cultural contexts involved in its emergence and transmission of a novel suicide method. This could provide valuable insights into the prevention of future emergent suicide methods.

Therefore, this systematic scoping review was aimed to (a) understand trends in suicide by charcoal burning in different regions; (b) summarize characteristics, risk factors, impact of media and suicide prevention strategies; and (c) identify research gaps and directions for future research. The review also presented and updated the recent trends and proportion of suicide by charcoal burning in Hong Kong, Taiwan, Japan and South Korea, where the method was reported as a common suicide method. By reflecting on the findings, we aimed to provide insights into how to prevent the spreading of charcoal burning as a suicide method, and how to flag other novel suicide methods before they become popular.

Methods

This study followed Guidance for Conducting Systematic Scoping Reviews and the searching process was in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) (Page et al., 2021; Peters et al., 2015).

Searching strategy

A search for articles on suicide by charcoal burning published from January 1998 to June 2021, was conducted through electronic library databases MEDLINE, EMBASE, SCOPUS, and PsycINFO. The start date was selected because the first charcoal burning suicide case was publicly reported in November 1998 (Chan et al., 2005). The search terms were as follows: (suicid*) AND (charcoal) for all databases.

Study selection

In total, 1,387 articles were identified from the four databases. First, duplicates were removed. Then, titles and abstracts of the remaining articles were reviewed by two authors independently (C.Y. and V.M.), and irrelevant studies were removed. Full texts for the potentially relevant articles were downloaded and screened independently by the same two authors.

Inclusion criteria

Articles describing prevalence, trends, characteristics, risk factors, impact of media, method dissemination and intervention strategies of suicide deaths by charcoal burning.

Exclusion criteria

Non-peer-reviewed articles, articles not published in English, studies that documented charcoal burning suicide attempts only or explored side effects/complications in charcoal burning suicide survivors, commentaries/editorials/letters, poster abstracts and systematic reviews and meta-analyses on suicidality that made passing reference to charcoal burning suicides among other suicide methods were excluded. Finally, the reference lists of all remaining articles were checked, and articles that met the inclusion criteria were added to the review evidence base. Discrepancies were discussed and resolved by the two authors.

Data extraction and synthesis

Information was extracted from included articles on: authors, year of publication, region(s) of study, study period, study population and sample size, study type and key findings. The information was categorized based on the pre-identified themes (trends/characteristics, risk factors, media impact and/or prevention strategies of charcoal burning suicide), and the study results were summarized in the results section and Appendix 1.

Trend of rate and proportion depiction

To depict the trend of charcoal burning suicide rate and the proportion of charcoal burning among all suicide methods in Hong Kong, Taiwan, Japan and South Korea, information (cross-region rates and proportions from 1998 to 2011) was extracted from Chang et al. (2014). Rates and proportions from 2012 onwards for Japan and South Korea were obtained and calculated from the World Health Organization (WHO) mortality database using the International Classification of Diseases, 10th revision (ICD-10) codes (X67 and Y17) (World Health Organization, 2022), in a manner consistent with Chang et al. (2014), while information for Taiwan and Hong Kong was retrieved from the Ministry of Health and Welfare in Taiwan (2021) and Hong Kong Coroner’s Court, respectively. Since only the number of suicides by gas were reported by the Ministry of Health and Welfare in Taiwan, this was used to estimate the rate and proportion of charcoal burning suicides from 2012 onwards, on the basis of a study suggested that a significant proportion of suicide by gas in Taiwan was attributed to charcoal burning (Lin et al., 2008).

Ethics approval statement

This research was approved by the Human Research Ethics Committee of the University of Hong Kong (EA210305).

Results

Study characteristics

The search identified 694 articles after removing for duplication. Through screening the titles and abstracts, 558 articles were considered as irrelevant. For the remaining 136 articles, 49 of them did not meet the inclusion criteria, and 87 studies were included in the review. Three potential articles were identified from the reference list of the included articles; however, full-text were not available for 2 of them, resulting in 88 articles included in the review. Figure 1 reports the PRISMA flowchart (Page et al., 2021). Most studies (N = 82, 93.2%) used quantitative methods, and the remaining studies employed mixed methods, supplementing the quantitative data with qualitative components such as content analysis or interviews with suicide survivors, family members or friends of suicide cases.

Figure 1.

PRISMA diagram of the search history.

Most research (N = 68) was from four East Asian regions (Hong Kong, Taiwan, Japan and South Korea). Appendix 1 summarizes the characteristics and key findings of the included studies.

Figure 2(a)–(c) respectively describe the annual charcoal burning suicide rates, the proportion of charcoal burning suicides among all suicide cases, and the number of research articles from Hong Kong, Taiwan, Japan and South Korea (1998–2020).

Figure 2.

Charcoal burning suicide rates, proportion of charcoal burning suicide (coded as ICD-9 E952 or E982, or ICD-10 X67 or Y17) among all cases and number of articles published in Hong Kong, Taiwan, South Korea and Japan, 1998–2020.

Articles on charcoal burning suicide

The first article on charcoal burning suicide was published in 2001 (Chung and Leung, 2001). Six articles investigating charcoal burning suicide in Hong Kong were published in the following 5 years. The majority of articles included in this review were published between 2007 and 2016, among which 29 of them documented the situation in Taiwan. There were few articles published between 2017 and 2020.

Trend of suicide by charcoal burning

The review findings suggest that suicide by charcoal burning has mainly occurred in Asia. This method was first reported in Hong Kong, then it appeared to spread sequentially to Taiwan, Japan and South Korea. It is now an established suicide method in these regions. However, Hong Kong, Taiwan and Japan appear to have passed the peak rates of suicide by charcoal burning, while the rate in South Korea continues to increase. The South Korean trends appear to be similar to those in the early days of this method adoption in Hong Kong (1998–2003) and Taiwan (2002–2006).

Hong Kong

The first case of charcoal burning suicide was publicly reported in November 1998, when a woman ended her life using charcoal in her bedroom. Starting from 1999 (2.6 per 100,000 population), the rate of charcoal burning suicide in Hong Kong increased until it peaked in 2003 (5.4 per 100,000 population), when the overall suicide rate was also at a historical high, then it steadily decreased to 1.5 per 100,000 population in 2011 (Chang et al., 2014, 2016; Chen et al., 2010b, 2015; Shek and Tang, 2003). Charcoal burning replaced hanging as the second most common method of suicide between 2001 and 2005 (Yip et al., 2003), accounting for 26.4% and 25.6% of all suicide cases in 2003 among adolescents and general population, respectively (Chang et al., 2014; Shek et al., 2005), and remained as one of the top three suicide methods in the community since then (Chang et al., 2019). Substitution effect was observed only among women, with the rate of charcoal burning increased and the rates for other methods decreased during 1997–2003 (Law et al., 2011a).

Taiwan

Suicide by charcoal burning emerged in 1998 (Lin and Lu, 2008), with a rate increase from 0.22 per 100,000 population in 1999 to its peak of 6.48 per 100,000 population in 2006, accounting for 33.5% of total suicide deaths (Pan et al., 2010). The emergence of charcoal burning suicide was the major contributor to the increase in the overall suicide rate (Law et al., 2011b; Thomas et al., 2011; Yip et al., 2012b), and there was limited substitution effect as the increase in charcoal burning suicide rate was not parallel with the drop in the rates of other suicide methods (Liu et al., 2007). Charcoal burning suicide began to decrease after 2006 (Chen et al., 2015). However, it remained the second most common suicide method in Taiwan (Chen et al., 2012a). Rates of charcoal burning suicide were reported to be higher in more urbanized areas, although no particular geographical origin was identified (Chang et al., 2010).

Japan

Charcoal burning suicide was first reported in 2003 and the rate reached the peak in 2008 (4.7 per 100,000 population) (Chang et al., 2014; Nabeshima et al., 2016). This resulted in an increase in the overall suicide rate among younger adults by 10–20% without observing a decrease in other method-specific rates, indicating no substitution effect (Yoshioka et al., 2014, 2016). Higher rates were observed in rural prefectures compared to urban areas (Yoshioka et al., 2016).

South Korea

There was a later emergence of this suicide method, compared to the other three East Asian regions. In 2007, charcoal burning suicide accounted for less than 1% of all suicide deaths; however, this proportion rapidly rose to about 8% in 2011 after extensive media reports of a celebrity suicide using this method (Chen et al., 2014; Ji et al., 2014). The prevalence of charcoal burning suicides increased from 0.06 per 100,000 population in 2006 to 1.97 in 2012 (Choi et al., 2014), although the overall suicide rate decreased from 2010 to 2016 (Chen et al., 2020). It became the second most common suicide method in the country in 2014 (Kim et al., 2019). This method has been more commonly observed in urban areas (Ji et al., 2014), although the gap between trends in urban and rural areas was decreasing (Chen et al., 2020).

Other regions

Suicide by charcoal burning in other countries seems relatively rare. Apart from the case reports from the four abovementioned Asian regions (Pan et al., 2009), other reports documented that charcoal burning suicide cases occurred in the Mainland China (Chen et al., 2019; Li et al., 2015, 2018; Lu et al., 2016), Macao, Malaysia, Thailand (Chang et al., 2014), Singapore (Chia et al., 2011), Czech Republic (Janík et al., 2017), Switzerland (Laberke et al., 2011), North Ireland (Lyness and Crane, 2011), Denmark (Nielsen et al., 2014), Tunisia (Nouma, 2021), Britain (Patel, 2008), Italy (Rossi et al., 2011) and Scotland (Brooks-Lim and Sadler, 2009). In addition, a study focusing on suicide by gases in England and Wales from 2001 to 2011 identified 38 suicide cases with charcoal burning (Gunnell et al., 2015). In the United States, charcoal burning suicide has rarely been reported (Azrael et al., 2016); however, a study exploring trends in carbon monoxide inhalation in King county, Washington, found that the proportion of charcoal burning suicides increased from less than 15% in 1996–1998 to as high as 40% in 2005–2009 (Schmitt et al., 2011). In Toronto, Canada, charcoal burning suicide cases increased by 533% from 3 cases in 1998–2003 to 16 cases in 2010–2015 (Sinyor et al., 2019). Meanwhile, charcoal burning suicide cases were mainly Asian ethnically in Toronto (Sinyor et al., 2019).

Characteristics

Charcoal burning had a relatively high case-fatality rate compared to other suicide methods such as poisoning and drowning ranging from 47% to 57% (Lee et al., 2014b; Yip et al., 2012b). Particularly, the case-fatality rate of charcoal burning in male was higher than that in female in Taiwan which might be due to the higher vigor possessed and the stronger determination to die among male (Lee et al., 2014b; Yip et al., 2012b).

Seasonal variations of charcoal burning suicide were observed. However, the results varied in which charcoal burning suicide peaked in spring in Hong Kong (Law and Leung, 2012), but in winter in South Korea (Ji et al., 2014; Lee et al., 2014a).

Risk factors

Distinctly different profiles have been described for people who died by charcoal burning suicide compared to those using other methods.

Sex

Yip et al. (2003) found no sex differences in suicide method choice between 1981 and 2001 in Hong Kong. Nevertheless, studies from 2001 onwards in Hong Kong suggested that males were more likely to adopt charcoal burning in Hong Kong (Chan et al., 2005; Chang et al., 2019). This concurs with findings from Canada, Mainland China, Taiwan, Japan and South Korea (Chang et al., 2010, 2016; Chen et al., 2012a, 2014; Cheng et al., 2015; Choi et al., 2014; Han et al., 2018; Ji et al., 2014; Kamizato et al., 2009; Lee et al., 2014a, 2014b, 2021; Pan et al., 2010; Sinyor et al., 2019; Yoshioka et al., 2014, 2016).

Age

Charcoal burning was more commonly used by younger and middle-aged adults irrespective of regions (Chan et al., 2005, 2009; Chang et al., 2019; Chen et al., 2014; Cheng et al., 2015; Choi et al., 2014; Han et al., 2018; Ji et al., 2014; Kamizato et al., 2009; Lee et al., 2014a, 2014b; Lin et al., 2010; Liu et al., 2007).

Comorbidities

There is inconclusive evidence about comorbidities. Some studies indicated that people who died by charcoal burning suicide were less likely to have pre-existing physical and mental health issues (Chan et al., 2005; Chang et al., 2019; Chen et al., 2009a; Kato et al., 2013; Leung et al., 2002; Pan et al., 2021; Sinyor et al., 2019). However, Chen et al. (2013a) found that those who died by suicide using charcoal burning in England had more contact with psychiatric services compared to people using other methods.

For those with multiple records of self-harm, people using charcoal burning previously would be more likely to adopt the same method in the subsequent attempts (Kuo et al., 2008, 2012) and had a higher risk of dying by suicide compared to those using drug overdose and self-cutting as the index method (Wang et al., 2015a, 2015b).

Socio-economic factors

A case-control study in Hong Kong suggested that people who died by suicide using charcoal burning during the emerging years of this method were more likely to be economically active, and have debt problems (Chan et al., 2005, 2009; Wong et al., 2010). This pattern has continued not only in Hong Kong, but also in other regions (Chang et al., 2016, 2019; Chen et al., 2007; Lee et al., 2006). Charcoal burning suicide was also prevalent among homicide-suicide and suicide pact cases (Cheng et al., 2015; Hon, 2011; Jiang et al., 2017; Leung et al., 2002; Pan and Lee, 2008; Wong et al., 2009a; Yip et al., 2009). Suicide notes were more commonly found among people who died by charcoal burning (Chan et al., 2005; Wong et al., 2009b). A positive association between unemployment rate and suicide by charcoal burning has been reported (Law et al., 2011a). Charcoal burning suicide was associated with the percentage of single-person household within the neighborhood (Lin et al., 2021).

Although charcoal burning has become a common suicide method in the community, some risk factors have changed over time. Married people in Hong Kong were more likely to adopt charcoal burning as a suicide method in 2002–2005; however, this observation changed in 2006–2013 (Chan et al., 2009; Chang et al., 2019). Furthermore, evidence from Taiwan and South Korea suggested that people living alone, and people who were single or divorced were more likely to adopt this method (Lee et al., 2014a; Chang et al., 2019; Choi et al., 2014; Ji et al., 2014; Lee et al., 2006; Pan et al., 2010). However, Chang et al. (2019) suggested that differences between people died by charcoal burning in Hong Kong, and people choosing other suicide methods, were diminishing.

Impact of media

Media has been identified as a major contributor to the spread of information on charcoal burning as a suicide method. In Hong Kong, an increasing number of suicides by charcoal burning followed in the next 2 months after the first report (Chung and Leung, 2001), which referred to the copycat effect. Similarly, a series of newspaper reports of charcoal burning suicide in Japan were associated with a number of suicide pacts using this method in the subsequent month (Yip and Lee, 2007).

In Taiwan, media reports of a young celebrity singer ended her life using charcoal burning in November 2008 triggered an immediate increase in charcoal burning suicides, especially among young people (Chen et al., 2010a, 2012b). Similarly in South Korea, a celebrity suicide using charcoal burning was widely reported by local media in September 2008 (Fu and Chan, 2013; Ji et al., 2014). The number of charcoal burning suicides dramatically increased within 1 month of his death (Ji et al., 2014), and this effect was long-lasting (Chen et al., 2014). It was also observed that people with similar demographics to this celebrity were more susceptible to charcoal burning suicide (Chen et al., 2014).

Besides apparent copycat responses to these well-reported cases of charcoal burning suicides, time-series analyses identified a positive relationship between media reports and charcoal burning suicides (Yang et al., 2013). In Taiwan, newspaper reports of charcoal burning suicides were associated with an increase in charcoal burning suicides the next day (Chen et al., 2013b). Similar relationships were identified in Hong Kong (Cheng et al., 2017) and South Korea (Lee et al., 2014a). A positive relationship was also identified in Mainland China and Taiwan between searching the Internet for information on charcoal burning and actual charcoal burning suicide cases (Chang et al., 2015; Cheng et al., 2015).

In the early days of this method, charcoal burning suicides were more likely to be over-reported because of the novelty (Chen et al., 2012c). Moreover, the information was often wrong and stereotyped. A study in Hong Kong found that media tended to report people who died by charcoal burning suicide as being less likely to have received mental health treatment, or to have previously attempted suicide, although the opposite was found in the psychological autopsy reports (Cheng and Yip, 2012). In the news, carbon monoxide was described as a ‘colorless, odorless, tasteless, and non-irritating gas’ (Huh et al., 2009). It was described as an ‘easy, quick, painless and non-violent’ suicide method (Chan et al., 2005; Lee et al., 2006), and the suicide act was depicted as ‘appealing’ (Chen et al., 2016).

Prevention strategies for charcoal burning suicide

Means restriction

One of the most common means restriction strategies for charcoal burning suicide is to lock up barbeque charcoal in retail outlets (Chen et al., 2015; Yip et al., 2010). Customers who want to purchase charcoal thus have to ask for help from shop assistants. This strategy has been practiced in Hong Kong (Yip et al., 2010), Taiwan (Chen et al., 2015) and South Korea (Jo et al., 2019), and appears to have been effective in the short term, as it restricts access to lethal means for impulsive suicidal people, and creates a buffer period.

However, a follow-up study evaluating charcoal restriction in New Taipei City indicated that the initial differences in charcoal burning suicides in intervention and control districts were no longer obvious 5 years later (Chang et al., 2021).

Suicide prevention for geographical hotspots

An offshore island in Hong Kong (Cheung Chau) has been identified as a geographical hotspot for charcoal burning suicides (Wong et al., 2009a). Visitors with suicidal intent rented holiday flats on the island for the purpose of suicide, and charcoal burning was the main method. To reduce suicide among visitors in Cheung Chau, a community suicide prevention program was established in 2002 (Wong et al., 2009a; Yip et al., 2021). Different stakeholders in the island such as police officers, social workers, holiday flat owners and the like were involved in the intervention, which raised their awareness and increased their knowledge about identifying people with suicidal intentions and assisted them to obtain support. Prevention strategies were promoted such as flat owners refusing to rent properties to persons who were alone and increasing patrols by police around the ferry pier. This resulted in a reduction in the number of suicides and attempted suicide cases by visitors (Wong et al., 2009a). Some of the strategies still remain in place over a decade later such as refusing to rent flats to a person who is by himself/herself only. A long-term evaluation of the intervention showed evidence of ongoing effectiveness, with number of charcoal burning suicide cases remaining lower than the pre-intervention level until 2017 (Yip et al., 2021).

Discussion

This systematic scoping review provides the first known summary of global trends in suicide by charcoal burning. Most of the research was from four East Asian regions, where charcoal burning appears to be a much common method of suicide than in other communities. One possible explanation may be the desire to preserve the whole body when dying in an Asian culture (Li et al., 2019). This preference could be related to a Confucius concept that the body is a valuable gift from parents. Therefore, people should keep the body intact for filial piety. Suicide by charcoal burning may be perceived as preserving the body and not damaging the appearance. The stereotypical and misleading belief that suicide by charcoal burning is ‘painless’ and people will look ‘peaceful’ just like falling asleep after dying makes this method more appealing to the Asian population.

Media reporting may also explain the clustering effect in East Asia. Geographical closeness and similar cultural backgrounds make it easier for news to spread and be believed. For example, news articles written in simplified/traditional Chinese can be read by people from mainland China, Hong Kong and Taiwan, and the phrase ‘charcoal burning suicide’ in Japanese also shares similar Chinese characters. This may also explain why charcoal burning suicide cases in Canada and other communities were mainly by Asian people.

From 2000, WHO has published handbooks on resources for media professionals, including guidelines and suggestions on responsible media reporting of suicide. Some of the recommendations include ‘do not explicitly describe the method used’, do not use ‘language which sensationalizes or normalizes suicide’, and include accurate information on help seeking (World Health Organization, 2017), which are all relevant to charcoal burning suicides. As a result, efforts have been made locally and internationally to improve media depiction of suicide (Beautrais et al., 2008; Fu and Yip, 2008; Nabeshima et al., 2016). For example, there are no longer pictures of suicide scenes or detailed descriptions of the suicide act. Meanwhile, when searching for keywords related to suicide on Google and other search engines, suicide prevention hotlines appear first in the results. Media engagement may also have contributed to the decrease in student suicides in Hong Kong which might be due to the decreased intensity in newspaper descriptive-reporting and increased intensity in preventive-reporting (Cheng et al., 2018). However, information on suicide methods is still widely available and easily accessible online (Cheng et al., 2015). More studies are needed to understand the impact of regulation on media reporting specifically on charcoal burning suicide.

The way in which information on charcoal burning as a suicide method has spread in Asian communities may provide insights that will assist in early detection of new suicide methods. When suicide cases using novel methods occur media should report this responsibly to avoid glorifying or stereotyping the act, or perpetuating myths. It is important to contain the spread of novel suicide methods early, for example, by restricting its reporting to avoid the copycat effect. However, once a new suicide method becomes established, a different approach should be adopted for its management. For instance, a range of stakeholders (government, healthcare professionals, social workers, local community, etc.) should be involved in the timely development of culturally and contextually specific prevention strategies. Suicide prevention for charcoal burning should be effective in reducing overall suicide rate since limited substitution effect was observed in previous research (Liu et al., 2007; Yip et al., 2012b; Yoshioka et al., 2014, 2016).

A public health approach should be adopted in addition to a high-risk approach. Community-based suicide prevention programs (Wong et al., 2009a; Yip et al., 2021) involving the local stakeholders could be implemented to prevent the spread of information on, and access to, the novel suicide method, and to develop safety networks for early detection and intervention for the vulnerable population (Lai et al., 2020). Prevention programs should be regularly enhanced after implementation to ensure sustainability, and to mitigate attenuation of effects, even if strategies had been effective in the early stages.

Apart from the strategies mentioned in the Results section, two reviews documented other community-based prevention strategies for charcoal burning suicide (Kim et al., 2019; Yip and Lee, 2007). Redesigning charcoal packaging to include warning messages and suicide prevention hotlines has been introduced in South Korea (Kim et al., 2019) and Hong Kong (Yip and Lee, 2007). Interventions into manufacturing processes of charcoal have reduced its lethality. The Ministry of Health and Welfare in South Korea has funded the development of safer charcoal emitting lower concentrations of carbon monoxide (Kim et al., 2019). This may widen the window of intervention by lengthening the time to reach the lethality level and allow more time for suicidal people to be discovered. However, the effectiveness of these strategies needs further investigation.

Limitations of the review

There are limitations in this review. First, articles in languages other than English were not included. Second, only published peer-reviewed journal articles were reviewed, as pre-print studies, unpublished studies, book chapters, theses and gray literature were not included. These may have provided important and additional information.

There were no specific ICD codes for suicide by charcoal burning until the 10th version of ICD (Chang et al., 2014; Hitosugi et al., 2009; Lin et al., 2008). Instead, E952/E982 in ICD-9 and X67/Y17 in ICD-10 (other gases and vapors) were commonly used to identify suicide by charcoal burning. This may have resulted in misclassification, or failure to capture the cases who actually died by charcoal burning. Moreover, the ICD code X67/Y17 included other methods such as suicide by hydrogen sulfide gas as both methods co-existed in Japan after 2007 (Yoshioka et al., 2014). This might affect longitudinal understanding of trends. However, previous research documented that 97.5% and 86.1% of all gas suicide in Hong Kong and South Korea, respectively, were charcoal burning suicide (Chang et al., 2016; Han et al., 2018).

Future directions

Studies outside Asia

Although charcoal burning may not currently be a common suicide method outside Asia, there are lessons to be learnt to avoid its spread or adoption in other communities. Reasons for regional difference in rates of suicide by charcoal burning should be explored.

Change in trends and case profiles

Studies looking at risk and protective factors for suicide by charcoal burning have identified similar patterns across regions. However, there is evidence that the profiles of charcoal burning suicide cases are changing in response to changing socioeconomic environments (Chang et al., 2019). The most recent study on charcoal burning suicides was from South Korea in 2016 (Chen et al., 2020), thus recent information from other countries is lacking. Moreover, there are few longitudinal or temporal studies regarding differences between suicide cases using charcoal burning or other methods. It is also important to explore the potential substitution effect of charcoal burning by other suicide methods with higher lethality, as community restrictions on purchasing charcoal may actually be counterproductive. In Hong Kong, the research publications have raised the awareness of media, government authorities and community stakeholders to participate in the suicide prevention efforts. Also, as shown in Figure 2, it seems that research output may be helpful in raising the awareness of the issue in the community, however, whether it can help to change the attitude and practice of preventing use of charcoal burning has yet to be determined.

Spatial pattern of charcoal burning suicide and the impact of area-level factors

While suicide by charcoal burning currently varies by urban and rural areas, and geographical hotspots have been identified, there is limited understanding of why this occurs. More research is required to understand differences in accessibility, availability and choices of suicide method, as well as geographical and socioeconomic patterns.

Most studies included in this review explored risk and protective factors of charcoal burning suicide at individual level. Potential meso- and macro-level factors such as social characteristics and economic situations, that could influence the use of charcoal burning as a suicide method, are not well researched. Future studies should explore meso- or macro-level factors such as unemployment, social deprivation and fragmentation, education or income inequality, on suicide by charcoal burning.

Media and advancement in technology

The role of media in charcoal burning suicide has largely focused on traditional media such as newspapers or Google search. No identified studies have analyzed the role of social media such as Facebook, Twitter, Instagram and Tiktok in charcoal burning suicide. With the advancement of technology, people can receive timely information from all over the world through different social media and instant messaging applications. Social media coverage and the copycat effect thus might spread more quickly and widely than a decade ago. Moreover, apart from the use of traditional analytical methods, more advanced methods such as the involvement of natural language processing and artificial intelligence will enable the detection and extraction of information from different sources in both traditional and social media. This will support a more comprehensive understanding of media effects on suicide by charcoal burning for early warning and intervention.

Sustainability of suicide prevention strategies

Current suicide prevention strategies for charcoal burning have adopted a public health approach, such as means restriction, which refers to the ‘limitation of access to lethal methods used for suicide’. This has been shown to be effective in the short term in different regions (Chen et al., 2015; Jo et al., 2019; Yip et al., 2010), however, the long-term effects are inconclusive (Chang et al., 2021). Further research is required to examine long-term effects and sustainability of means restriction. Moreover, there may be a barrier to this prevention strategy in the long term as retailers may be reluctant to lock up charcoals due to fear of loss of business (Wong et al., 2009a). Collaborations between government and retailers will be required to promote and enforce restricting access to charcoal, and to promote alternate, more environmentally friendly fuels such as gas (Yip et al., 2012a).

Conclusions

Suicide by charcoal burning has grown from a novel used by one person in Hong Kong to a pandemic in East Asian regions, accounting to date, for more than 100,000 deaths. This represents a painful lesson for East Asian communities. Longitudinal and up-to-date research is required to better understand the characteristics of people who died by suicide by charcoal burning, why this method was chosen and how best to prevent it, in the short and longer-term. This review provides insights into how to respond earlier and more effectively to future novel suicide methods, such as engaging the media to report responsibly, conducting intervention research, and involving multiple community stakeholders when developing prevention strategies.

Footnotes

Appendix 1

Summary of reviewed publications.

Authors	Year	Region(s)	Study period	Study population (sample size)	Study type	Key findings
Azreal et al.	2016	USA	2005–2012	80,715 suicide cases in 16 states	Time-series	A small non-significant increase in CB suicide over the study period.
Brooks-Lim et al.	2009	Dundee, Scotland	2005–2008	Three CB suicide cases	Case report	Three cases were identified in confined spaces (an outbuilding, a car and a bedroom).
Chan et al.	2005	Hong Kong	1998.11–2000.1, 2000.12–2002.1	160 CB suicide cases with 160 age- & sex-matched controls by other methods 25 CB suicide attempters	Mixed-method	People who killed themselves using CB were more likely to be male, aged 25-54, economically active, physically and mentally healthy. CB suicides were more likely to be associated with debt issue and left with suicide notes. Media played a role in the spreading of the method, describing CB as an “easy, painless and effective” method.
Chan et al.	2009	Hong Kong	2002–2004	150 aged 15-59 suicide cases and their informants	Mixed-method	People who killed themselves by CB were more likely to be married or divorced, aged 31-45, facing unmanageable debt, and receiving psychiatric treatment within 6 months before death compared to those died by other methods.
Chang et al.	2010	Taiwan	1991-2007	Age-standardized suicide rates in townships	Spatial and temporal	Proportions of CB suicide among all suicide cases increased from 0.1% in 1991 to 26.6% in 2007. CB rates of male were higher than female. Higher CB rates were observed in urban areas than rural ones without a point of origin.
Chang et al.	2014	East/Southeast Asia	1995/1996–2011	Age- and sex-specific suicide rates in Hong Kong, Japan, South Korea, Taiwan, Singapore, Malaysia, the Philippines, and Thailand	Time-series	CB suicides accounted for less than 1% of all suicides in Hong Kong, Taiwan, South Korea and Singapore, and 5% in Japan in 1995/1996, but increased to 13%, 24%, 7%, 5%, and 10% in 2011 respectively. Rises were seen in Hong Kong after 1998, in Singapore in 1999, in Taiwan in 2000, in Japan in 2002, and in South Korea in 2007. No marked increases were observed in Malaysia, the Philippines and Thailand.
Chang et al.	2015	Taiwan	2008–2011	Suicide cases, suicide-related Google search volume, and number of articles reporting suicide in four newspapers	Time-series	An increase of 4.3% in CB suicide incidence in the same week and 3.8% in the subsequent week were associated with every 10% increase in Google searches. A 3.6% increase in CB suicide in the same week was associated with a one-article increase in a newspaper.
Chang et al.	2016	Hong Kong	2005–2013	Suicide cases from Coroner’s Court reports	Time-series	About one sixth of all suicides involved gases, in which 97.5% were CB. A 33% decrease of CB was recorded from 2005 to 2013. CB suicide was similar to helium suicide among which CB cases were younger and associated with debt issues compared to suicides by other methods.
Chang et al.	2019	Hong Kong	2002–2013	Suicide cases from Coroner’s Court reports	Time-series	CB cases were more likely to be male, aged 30-49, with debt issues, living alone, and less likely to have physical illnesses or received psychiatric treatment compared to suicide cases died by other methods. Compared to CB cases in 2002-2005, cases in later periods were more likely to receive current psychiatric treatment or with medical illness and were less likely to be married, unemployed or with debt issues. The characteristics of CB and other methods have become similar through time.
Chang et al.	2021	Taiwan	2000–2017	Quarterly age-standardized CB and overall suicide rates	Time-series	No differences were observed in suicide rates and step changes in rates in overall and CB between the intervention and comparison cities before and after the voluntary actions of large chain retail stores moving charcoal bags into locked cabinets.
Chen et al.	2007	Hong Kong	2002.08–2004.12	148 suicide cases and their informants	Mixed-method	CB cases were associated with debt issues, chronic stress, better problem-solving ability, no psychiatric illness and suicide deliberation.
Chen, Lee et al.	2009	Taiwan	2000–2004	12,391 adult suicide cases	Cross-sectional	CB suicides were less likely to be used by people diagnosed with psychiatric disorders compared to other methods.
Chen, Park et al.	2009	South Korea, Sweden, Taiwan and the USA	2002	Age- and method-specific female suicide rates	Cross-sectional	CB suicide was uncommon outside Asia. A high proportion of women aged 15-44 in Taiwan used CB.
Chen, Yip et al.	2010	Hong Kong, Taiwan	1997–2007	Monthly suicide mortality data from Department of Health of the Executive Yuan of Taiwan and the Coroner’s Court of Hong Kong	Time-series	CB suicide rates declined in Hong Kong for the period 2003-2007, while the CB suicide rates continued to rise in Taiwan during the period.
Chen, Tsai et al.	2010	Taipei City	2008	63 suicide attempters from case registry for 4 weeks after a suicide case of a female singer	Mixed-method	43 of the 63 attempters encountered the news, and 16 of them reported their suicide attempts were influenced by the news report. For those encountered the news, the odds of using CB were 7 times higher than those using drug overdose.
Chen, Yip et al.	2012	Taiwan	2009	Suicide news reports from four major newspapers and suicide mortality data from the Department of Health	Cross-sectional	Over-reporting of CB in media was more common in female due to considerable number of articles regarding suicide pacts and maternal filicide-suicide.
Chen, Kwok et al.	2012	Taipei City, Taiwan	2004 and 2006	Non-fatal self-harm presenting to the emergency department in 2004 (n = 2237) and 2006 (n = 3141); suicide cases from the Death Certification System of Department of Health in Taiwan in 2004 (n = 346) and 2006 (n = 453)	Decomposition	CB replaced hanging as the most common suicide method in 2006. Increase of incidence in CB contributed to the widening male-to-female suicide ratio.
Chen, Liao et al.	2012	Taiwan	2006–2008	Suicide mortality data from the Department of Health of the Executive Yuan of Taiwan	Time-series	Suicides using CB increased significantly among the young age group and in females 2 week after extensive media report of a 24 year-old female singer killed herself by CB.
Chen, Bennewith et al.	2013	England	2005–2007	All possible cases of CB suicides from 12 Coroners	Cross-sectional	11 CB cases were identified. CB cases were younger, more likely to be unemployed and unmarried. Over one-third of CB cases obtained information of the method from the internet. CB cases were more likely to have psychiatric service contact compared to people using other methods.
Chen, Chen et al.	2013	Taiwan	1998–2002	News articles related to suicide and suicide method in two newspapers (n = 5,587); data on suicide deaths from official death records	Time-series	Every CB news article was associated with a 16% increase in CB suicide in the following day, while reporting in other suicide methods was not associated with their incidences. The reporting intensity of CB suicide decreased after 2002, however, the incidence of CB suicide remained high.
Chen et al.	2014	South Korea	2007.09–2009.12	Suicide mortality from the Statistics Korea	Time-series	CB accounted for 0.85% of all suicides in a year before a celebrity killed himself by CB, and the method contributed to 4.8% of all suicides after a year of the death of the celebrity. CB cases were more likely to be male and those aged 45 or below.
Chen, Chen et al.	2015	Taiwan	2009–2013	Suicide mortality data from Taiwan’s national cause-of-death file	Quasi-experimental	Compared to the period before mandatory removal of barbecue charcoal from open shelves to locked storage in major retail stores, CB suicide rate reduced by 30% in the experimental area, while no significant reduction was observed in the control cities. No compensatory increase of other suicide methods was observed in the experimental site.
Chen, Yip et al.	2015	Hong Kong and Taiwan	1998–2010	Suicide mortality data of aged 15 or above from Taiwan’s national cause-of-death file, Hong Kong Census and Statistics Department and Coroner’s Court in Hong Kong	Time-series	In Hong Kong, CB suicide elevated rapidly in the onset period. It reached the peak after 5 years, and then decreased afterwards. In Taiwan, CB suicide increased at a relatively slower and peaked after 8–9 years but remained at a high level up to 2010.
Chen et al.	2016	Taiwan	1998–2002	301 news reports from two newspapers covering 260 CB events; suicide data from official death records	Mixed-method	The number of reports per suicide was higher during the rapid increasing stage of CB compared to the early initial stage. Detailed reports of CB were associated with increased CB suicide afterwards. Later reports provided more detailed descriptions toward the setting and CB was glamourized.
Chen et al.	2019	Sichuan, China	2008–2016	237 non-fire related CO poisoning deaths	Cross-sectional	10.5% of all cases were determined to be suicide. Among all suicide cases, 68% used coal or CB.
Chen et al.	2020	South Korea	2001–2016	Suicide data from the South Korean National Death Registration	Time-series	Although the overall suicide rate decreased during 2010-2016, the CB rate continued to increase. In 2014-2015, CB became the second most common method of suicide, accounting for 14% of all suicides. The urban-rural difference in CB suicide rate has decreased between 2012 and 2016.
Cheng et al.	2012	Hong Kong	2002.08–2004.12	Newspaper articles from five major newspapers reporting 150 aged 15-59 suicide cases	Cross-sectional	CB cases were more likely to be associated with debt issue and being single, which were reflected by the news articles. CB cases were less likely to be associated with unemployment and more likely to be associated with having previous attempts or receiving mental health treatment, but the news articles reported the opposite trend.
Cheng et al.	2015	Mainland China	1998–2014	CB news articles from 335 newspapers (1998-2014); online search trend in Baidu (2011-2014); 292 search results in Baidu	Mixed-method	170 newspapers articles reporting 109 CB attempts (89 fatal) from 13 provinces were identified. Higher proportion of the cases were male, aged 30 and below, occurred in a hotel, in Guangdong Province, and involved suicide pacts. An increase in CB news articles was identified over time. Provinces with higher rates of publicized CB suicide have higher internet search rates. Detailed information of CB method is widely available and easily accessible online.
Cheng et al.	2017	Hong Kong	1998–2005	Suicide cases from Coroner’s Court and Census and Statistics Department; suicide news articles from four newspapers	Time-series	A CB suicide news article was associated with 0.562 subsequent CB suicide case. A CB suicide case was associated with 0.122 subsequent CB suicide case.
Chia et al.	2011	Singapore	2000–2004	All suicide cases from Coroner’s Court	Cross-sectional	6 CB suicide cases were identified.
Choi et al.	2014	South Korea	2006–2012	Suicide data from Statistics Korea	Time-series	The age-standardized rates of CB increased from 0.06 in 2006 to 0.48 in 2008 and 1.97 in 2012 per 100,000 population. CB suicides were associated with being male, among younger age groups, being single or divorced, with high education and with non-manual jobs, with reference to other suicide methods.
Chung et al.	2001	Hong Kong	1998–1999	Articles from six newspapers	Time-series	The first CB case was reported in November 1998. 56 CB cases were reported with 39% of them occurred within nine weeks after the first report. All CB cases used barbecue charcoal and 90% of them occurred at home. CB cases were younger compared to jumping and hanging cases, but no significant sex differences were observed.
Fu et al.	2013	South Korea	2003–2009	Media reported suicides of the South Korean entertainment celebrities	Time-series	One out of thirteen celebrities killing themselves used CB which did not result in subsequent statistically significant increase of suicide rate.
Gunnell et al.	2015	England and Wales	2001–2011	Suicides and deaths of undetermined intent from the Office of National Statistics	Time-series	38 CB suicide cases were identified during the study period. CB cases increased from 1 in 2001-2002 to 11 in 2010-2011.
Han et al.	2018	South Korea	1991–2015	Suicide data from Statistics Korea	Time-series	CB accounted for 86.1% of all gas poisoning suicides. Among all suicide methods, only CB increased in 2011-2015. CB suicide was more common among males aged 45 or below.
Hon et al.	2011	Hong Kong	1998–2010	14 cases of filicide-suicide cases	Case Report	One CB suicide case involved a couple, a 3 year-old girl and a 3 month unborn fetus was reported.
Huh et al.	2009	South Korea	2007–2008	Seven cases of imitative suicide	Case Report	Three cases of CB suicide occurred within 3 months after an accidental death of CB poisoning, and other four cases in the same season in the next year. This may be due to the mass media reporting of describing the circumstances of the accident in detail and focusing on the characteristics of CO as a colorless, odorless, tasteless and non-irritating gas.
Janík et al.	2017	Czech Republic	1947–2006	All fatalities caused by CO poisoning	Case Report	There were suicide cases by CB.
Ji et al.	2014	South Korea	2000–2011	Suicide records from the Statistics Korea (n = 138,938)	Time-series	Proportion of CB among all suicide cases was 0.7% in 2007 and rapidly elevated to 7.9% in 2011. The most important risk factor of CB suicide was the media report of a celebrity suicide case. Other risk factors included being male, aged 15-64, living in the urban area, being unmarried, divorced or bereaved, and in winter season.
Jiang et al.	2017	Mainland China	Before 2015.6.1	62 Internet suicide pacts involving 159 cases	Cross-sectional	Over 80% of all cases were CB suicide, and they mainly occurred in hotels and rental housing.
Jo et al.	2019	Gyeonggi Province, South Korea	2000–2016	Suicide data from the National Statistical Office	Time-series	The charcoal-selling procedure improvement campaign was a significant intervention for reducing the number of CB suicides.
Kamizato et al.	2009	Okayama, Japan	2002–2003	824 suicide cases	Time-series	30 CB were identified with potential time-clustering pattern. High incidence of CB was observed among men aged 35-44.
Kuo et al.	2008	Taiwan	2004–2005	5,261 suicide attempters	Cohort study	Use of CB at the index attempt was associated with subsequent suicide deaths and used the same means in a subsequent attempt leading to death. About 60% who died from CB suicide has used a different method at their index attempt.
Kuo et al.	2012	Taiwan	2004–2006	7,601 self-harm individuals	Cohort study	Compared to individuals who took an overdose, those used CB as the index episode had a higher risk of subsequent suicide deaths. Those who used CB in the index attempt tended to use the same method at the subsequent suicide attempt leading to death.
Laberke et al.	2011	Switzerland	2010	2 CB suicide cases	Case report	A suicide pact (a man and a woman) using CB was found.
Law, Yip & Caine	2011	Hong Kong	1997–2007	Suicide data from Coroner’s Court records (n = 10,660)	Time-series	18.3% of suicide cases used CB. Every percent increase in unemployment rate was associated with an increase of CB suicide by 36.4%. During 1997-2003. 73.2% and 78.1% of the increase in male and female suicide rates respectively were attributable to increase in CB suicides. During 2003-2007. 57.9% and 34.3% of the decrease in male and female suicide rates respectively were attributable to decrease in CB suicides. During 1997-2003, a means substitution was observed only among women, in which the CB rates increase while rates for other methods decreased. During 2003-2007, the overall suicide rate dropped, and all method-specific rates decreased.
Law, Yip & Chen	2011	Taiwan	1997–2007	Official death records from the Department of Health of the Executive Yuan of Taiwan	Time-series	Increase in CB accounted for 50.9% of the increase of potential years of life loss (PYLL) from suicide.
Law et al.	2012	Hong Kong	2001–2008	Suicide data from registered death files (n = 1,649)	Time-series	A peak of CB suicide was observed in April and on Monday.
Lee et al.	2006	Hong Kong	2000–2002	160 CB suicide cases with 160 age- & sex-matched controls by other methods	Mixed-method	CB suicide has led to an increase in suicide rate among the middle-aged. People who were unmarried and living alone were more likely to choose CB suicide. CB suicide cases were more likely to have gambling and debt problems. The media reported CB as an easy and comfortable way of dying and legitimized it as a solution for financial problem.
Lee, Ahn et al.	2014	South Korea	2007–2011	CB suicide cases during the study period (n = 3,101); weekly information on CB posted on Internet	Time series, cross-sectional	The incidence of CB suicide has increased during the study period. Male, younger, highly educated people and those living in urban area were more likely to choose CB. CB suicides were more likely to occur during October to December. There was a positive correlation between CB suicide and media report on CB suicide.
Lee, Wu et al.	2014	Taiwan	2006–2010	All people with suicide attempt registered in a surveillance database during the study period (n = 2,524)	Cohort study	Case fatality rate for CB suicide was 50.1%. Males, single and younger people were more likely to choose CB suicide. Among CB suicide cases, people aged 35-64 had higher case fatality.
Lee et al.	2021	Taiwan	2001–2005	Individuals with methamphetamine use disorder during the study period (n = 23,248)	Cohort study	The incidence of CB suicide was higher among men.
Leung et al.	2002	Hong Kong	1996–1999	Completed suicide cases from death registry and hospital authority (n = 2,284)	Time series, cross-sectional	CB was common among suicide pacts. CB suicide cases were younger and less likely to have mental illnesses compared to people using other methods.
Li et al.	2015	Wuhan, China	2009–2014	Case information of CO poisoning deaths from police departments in nine districts (n = 156)	Cross-sectional	66.7% of all CO poisoning suicide cases used coal or CB.
Li et al.	2018	China	Before October, 2016	193 incidents of online broadcast of suicidality	Cross-sectional	8 cases of CB suicide were identified.
Lin et al.	2008	Taiwan	1971–2005	Suicide mortality aged 15 and above	Time-series	Since 1998, CB suicide was observed in Taiwan.
Lin et al.	2010	Taiwan	2002–2008	Suicide statistics Taiwan	Spatial and temporal	CB has become the leading method in some regions during 2006-2008. CB was more common among younger people.
Lin et al.	2021	Taiwan	2004–2010	Suicide statistics among people aged 10 and above in Taipei City	Ecological study	CB suicide was associated with single-person household within the neighborhood.
Liu et al.	2007	Hong Kong and urban Taiwan	1983–2002	Suicide statistics from Hong Kong and Taiwan	Time-series, cross-sectional	A rapid increase of CB suicide was detected between 1998 and 2002 in Hong Kong and urban Taiwan. The increase in CB suicide was associated with overall suicide increase, and not parallel with decrease with other suicide methods, indicating limited substitution effect. Excess CB cases were found among those aged 24-39.
Lu et al.	2016	Pudong, China	2005–2014	176 CO poisoning death cases	Cross-sectional	37 cases of CO-related suicide were identified with 36 of them used coal or CB.
Lyness et al.	2011	North Ireland	2006–2008	4 CO poisoning death cases	Case report	Two CB suicide cases were identified.
Nabeshima et al.	2016	Japan	2003–2010	All news reports on CB and hydrogen sulfide suicide during the study period (n = 4007)	Time-series, cross-sectional	The mean violation score for news reports on CB suicide was 3.2 during the study period.
Nielsen et al.	2014	Demark	2008–2012	19 CB death cases	Case report	11 suicide cases and 2 filicide-suicide cases were identified.
Nouma	2021	Tunisia	N/A	A CB suicide case	Case report	A 28 year-old man killed himself using CB.
Pan et al.	2008	Taiwan	1999–2006	National mortality data during the study period	Time-series, cross-sectional	An increasing trend of CB suicide was identified among female aged 25-44 during the study period. The increase of maternal filicide-suicide was parallel with the increase of CB suicide. CB suicide was the dominant method in maternal filicide-suicide.
Pan et al.	2009	Taiwan	2000–2008	1011 cases of physician’s deaths	Case report	17 definite suicide cases were identified and 5 of them used CB.
Pan et al.	2010	Taiwan	1995–2006	Population statistics and national mortality data during the study period.	Time-series, cross-sectional	The incidence of CB suicide has increased from 1999 to 2006. CB has become the second most common method since 2004. Younger, male, divorced and single people were more likely to choose CB over other methods.
Pan et al.	2021	Taiwan	2001–2016	Patients with schizophrenia (n = 170,433) and suicide cases among the general population (n = 59,013)	Cohort study	Patients with schizophrenia were less likely to kill themselves with CB compared to the general population.
Patel	2008	Britain	NA	One CB suicide case	Case report	A young woman living alone was found killing herself with an extinguished barbecue charcoal in a sealed bathroom. Suicide note was found.
Rossi et al.	2011	Italy	2005	One CB suicide case	Case report	A 48 year-old man killed himself using CB in the office bathroom.
Schmitt et al.	2011	The United States	1996–2009	All CO suicide cases in Kings County during the study period (n = 158)	Time-series	The trend of CB suicide has been increasing during the study period.
Shek et al.	2003	Hong Kong	1980–2000	Statistics from the Census and Statistics Department	Time-series	CB suicide became more popular in the 1990s.
Shek et al.	2005	Hong Kong	1980–2003	Statistics from the Census and Statistics Department	Time-series	There was a rising trend of CB suicide among Hong Kong adolescents.
Sinyor et al.	2019	Canada	1998–2015	Suicide cases from the Coroner’s Court records (n = 4,062)	Time-series, cross-sectional	Compared to 1998-2003, there was a large increase in CB suicide in 2010-2015. Most CB suicide cases were Asian.
Thomas et al.	2011	Taiwan	1999–2006	Sex-specific mortality and population data	Time-series	The increase in CB suicide was associated with the increase in the overall suicide rate during the study period.
Wang, Huang et al.	2015	Taiwan	2006–2010	All individuals with non-fatal suicidal attempt who registered in the surveillance system (n = 2,052)	Cohort study	People who used CB at the index attempt had a higher risk of subsequent suicide death.
Wang, Wu et al.	2015	Taiwan	2006–2011	All individuals with non-fatal suicidal attempt who registered in the surveillance system (n = 2,496)	Cohort study	People who used CB at the index attempt had a higher risk of subsequent suicide death. People used CB at index were more likely to accept the case management services.
Wong, Liu et al.	2009	Hong Kong	1998–2006	Police records of suicides and attempted suicides on three islands	Intervention study	The number of CB suicides reduced from 29 during the period prior to program implementation to 5 after the program implementation.
Wong, Yeung et al.	2009	Hong Kong	2000	Suicide cases from the Coroner’s Court records (n = 902)	Cross-sectional	CB suicide cases were more likely to leave suicide notes.
Wong et al.	2010	Hong Kong	2003	Coroner’s court files of suicides (n = 1,201)	Cross-sectional	Gambling with related debt suicides were more likely to use CB.
Yang et al.	2013	Taiwan	2003–2010	All suicide cases from the Department of Health (n = 31,364) and all suicide news from Google News	Spatial and temporal	Reporting CB suicide news has led to a copycat effect on CB suicide.
Yip et al.	2003	Hong Kong	1981–2001	Data on registered death	Time-series	The proportion of CB suicide has increased from 6.0% before 1998 to more than 28.0% in 2001. CB has replaced hanging as the second most common suicide method.
Yip et al.	2009	Hong Kong	1989–2005	98 homicide-suicide cases	Cross-sectional	22% of the homicide-suicide cases used CB.
Yip et al.	2010	Hong Kong	2006	Two regions in Hong Kong	Quasi-experiment	All barbeque bags were removed from open shelves in the intervention region. CB suicide rate was reduced significantly in the intervention region compared to the controlled region.
Yip et al.	2012	Taiwan	2004–2006	All suicide cases in Taipei City	Time-series	During the study period, the CB suicide rate has increased by 91.9% among males and 87.0% among females. Case fatality rate for CB has decreased from 57% in 2004 to 47% in 2006. Case fatality rate for CB was higher among males than females.
Yip et al.	2021	Hong Kong	2007–2017	Coroner’s Court records	Time-series, cross-sectional	A hotspot of CB suicide was identified in Hong Kong. Visitors were more likely to use CB compared to residents.
Yoshioka et al.	2014	Japan	1998–2007	CB suicide mortality	Time-series	CB suicide has led to an increase in overall suicides among males and females aging 15–44 years, with no substitution effect detected.
Yoshioka et al.	2016	Japan	1999–2013	CB suicide mortality	Spatial and temporal	CB suicide increased in mid-2000. No substitution effect was detected. CB suicide was more concentrated in rural area and among males.

USA: The United States of America; CB: Charcoal burning; CO: Carbon monoxide; PYLL: Potential years of life loss; NA: Not applicable.

Author Contributions

C.Y.Y.: Conceptualization; data curation; literature search; formal analysis; methodology; visualization; writing—original draft; writing—review and editing.

V.Y.M.: Conceptualization; data curation; literature search; formal analysis; methodology; visualization; writing—review and editing.

P.S.F.Y.: Conceptualization; funding acquisition; supervision; writing—review and editing.

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This research is supported by the Humanities and Social Sciences Prestigious Fellowship Scheme (project number: 37000320) and the General Research Fund (project number: 17606521). The funding sources have no roles in study design, collection, analysis and interpretation of data; in writing of the articles; or in the decision to submit it for publication.

ORCID iD

Cheuk Yui Yeung

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