To our knowledge, the present study is the first to investigate the temporal patterns of charcoal burning suicide. As charcoal burning is a non-violent suicide method that requires planning to avoid rescue intervention [1–3], the temporal variations in suicide observed in this study contradict the findings of many published studies that suicide seasonality only exists in relation to violent methods [8, 16, 17]. This suggests that the specific suicide method is an important factor of suicide seasonality, and that the simple differentiation between violent and non-violent methods is not applicable to the interpretation of suicide seasonality in Hong Kong . In fact, a range of published studies have demonstrated that temporal variations in suicides are method-specific [13, 29, 30]. Future research on temporal patterns of suicide should be more method-specific.
Previous studies have attributed the monthly patterns observed in suicide rates to the influence of seasonality-linked biological, psychosocial and meteorological correlates [12, 16, 17, 31]. As the April peak in the seasonality of suicide has also been observed in other suicide methods, charcoal burning suicides may share some of the common causes of suicides by other methods. In addition to the presence of spring peak in April, it is observed that attempters were more likely to commit suicide by burning charcoal in the colder winter months. From a practical point of view, the sub-tropical climate of Hong Kong would implicitly discourage suicide attempters from burning charcoal in summer to take their own lives. By contrast, the cooler temperatures in winter would make charcoal burning a more acceptable option for suicide. However, the extent to which these explanations are able to account for the monthly pattern of charcoal burning suicides remains unclear. Some studies suggest that the correlation between biological factors and seasonal variation is only observed in violent suicides [32, 33]. Furthermore, the findings on the effects of meteorological variables on suicide seasonality are rather inconsistent and have not been replicated in subsequent studies [10, 34]. It is worth noting that only employed women tended to commit suicide by burning charcoal in spring (i.e., April). Hence, the seasonal occurrence of particular mental disorders involving suicide ideation fails to explain the temporal variations in charcoal burning suicides. In fact, this is in line with the observation that charcoal burning suicide victims were less likely to be associated with psychiatric illness or substance abuse, compared with those who killed themselves using other methods [1–5]. We expect that more detailed data on the events prior to the death of charcoal burning suicide completers, and on what the suicide attempters were thinking, will help us to explore this knowledge gap in future studies.
The results confirm our hypothesis concerning the daily pattern of charcoal burning suicides. The risk of charcoal burning suicide was found to be higher on weekdays (i.e., Monday, Tuesday, and Thursday) than on weekends. This is consistent with most of the other published findings, which report a peak at the beginning of the week [14, 15, 35, 36]. As suggested by Erazo et al. , a significantly higher rate of suicide on Monday seems to be best explained in terms of socio–psychological variables. Relatively speaking, a sense of personal failure and isolation is more likely to be triggered in a depressive person at the beginning of the working week, when their surroundings reflect their duties . A recent study on the relationship between the weekend, work, and well-being also indicated that both men and women tended to experience an enhanced sense of well-being during the weekend compared with working days . Yet, the second peak on Thursday observed in the present study is rather novel in the literature. Further investigation of the relationship between weekdays and psychological stress is warranted.
In line with our expectations, there were pronounced differences in the temporal patterns of charcoal burning suicides in relation to sex. The results identified marked peaks in the rates of charcoal burning suicide in spring and winter (January, February, April, May and November) for working-age women, a less obvious spring peak with a summer nadir was observed for working-age men. This seasonal difference in the magnitude of variation] may be further explained by gender differences in relation to thermal comfort. In an earlier physiological study, Lan et al.  found that Chinese women were more sensitive to temperature differences than men and that women preferred a relatively warmer environment because they had a higher comfortable operative temperature. It can thus be expected that women are more inclined to burn charcoal in “cold months” and men are less likely to do so in “hot months”. As our knowledge of the determinants of charcoal burning suicide remains scant, further research is needed to investigate the differential effects of charcoal burning on vulnerable men and women in terms of monthly patterns.
It is worth noting that the influence of employment status on monthly and daily patterns of charcoal burning suicides differed considerably between men and women. According to our data, the monthly variations in suicide risk were more pronounced for non-working men and working women, whereas the daily variations were more apparent for working men and non-working women. It appears that economic activity status either strengthens or weakens the magnitude of the temporal variations in charcoal burning suicide, rather than serving as a determinant that alters the temporal distribution. This may indicate that active employment only serves as a stabilizing factor that protects individuals from various life-threatening forms of behavior (e.g. alcohol consumption or misuse of illicit drugs)  and thereby implicitly influences the timing of suicide among specific groups of individuals, but not the whole population. Accordingly, the nature and magnitude of these effects should be recognized in future studies to develop a more effective approach to suicide prevention in Hong Kong.