Temporal and seasonal variation in the occurrence of chemical incidents.

AIMS To determine whether there were temporal or seasonal patterns in the occurrence of chemical incidents reported to the West Midlands Chemical Incident Surveillance System, UK. METHODS A retrospective analysis of reports maintained on a computerised database was carried out for information received from January 1997 to December 2001. RESULTS Annual numbers of events increased significantly from 77 (7.5%) in 1997 to 282 (27.4%) in 2001. Compared to the average of other seasons, proportionately more incidents occurred in the summer (29.3%). Compared with the average of other days, incidents were more likely to occur on Thursdays (17.1%) and least likely on Saturdays (8.9%). When grouped together on a six hourly basis incidents were most frequent between 12 00 and 17 59 (31.1%) and least frequent between 00 00 and 05 59 (21.2%). CONCLUSIONS The surveillance system shows that chemical incidents do not occur randomly but have marked temporal and seasonal variation. These results have implications for service provision, training, and the development of preventive strategies.