br Introduction Persons entering confined spaces are at risk

Introduction
Persons entering confined spaces are at risk of a variety of health hazards. These hazards stem from the restricted volume of space inside such spaces and the small dimensions of the opening to the outside environment, with consequent difficulty in obtaining access to and exiting from the space, or a combination of the two. These features readily predispose those entering a confined space to exposure to changes in the atmospheric composition within that space, which may be harmful to their health. Confined spaces are most commonly encountered in work situations, and include sewers, casings, tanks, silos, vaults, tunnels, and compartments of ships [1–4].
A common atmospheric change occurring in confined spaces may involve a reduction in the volume percent of oxygen, as a result of oxygen-consuming reactions within the space, replacement of oxygen by other gases, or build-up of toxic gases. Persons entering a confined space may be incapacitated or may even die as a result of these atmospheric changes. While normal Bisindolylmaleimide V cost close to earth contains 20.9% of oxygen by volume, the Occupational Safety and Health Administration regulation and many confined-space guidance documents indicate that an atmospheric oxygen concentration of 19.5% is the lowest level acceptable for entry into such spaces [2,3].
A number of investigation reports have given data on fatalities in confined spaces. In the United States of America, the Division of Safety Research of the National Institute for Occupational Safety and Health is currently conducting the Fatal Accident Circumstances and Epidemiology project, which focuses primarily on selected electrical- and confined space-related fatalities [5,6]. Suruda et al. [7] analyzed data from the National Traumatic Occupational Fatalities surveillance system, which the National Institute for Occupational Safety and Health had assembled. During the 10-year period between 1980 and 1989, 585 separate fatal incidents occurred in confined spaces, claiming 670 victims. Seventy-two (12%) of the fatal incidents involved multiple victims.
In Thailand, cases of death in confined space occur almost every year. Between 2004 and 2008, there were eight investigation reports of 34 deaths and injuries in confined spaces [8]. An estimated 60% of the fatalities involved would-be rescuers. These rescuers had tried to help someone who had collapsed, but presumably had not given due consideration to the reason for the collapse. In one event, in 2006, three farmers died in a shallow well in a field in Kamphaengphet province, northern Thailand. According to the investigation report, local health officers who measured the gas content of the atmosphere at the bottom of the well 6 days later found the oxygen level to be only 5.9% [9]. The Bureau of Occupational and Environmental Diseases, Ministry of Public Health, then measured oxygen levels in 57 other shallow wells in the same region and found that 16% had low levels of oxygen (0.3–16%), which would have posed a hazard to anyone entering them, although toxic gases were not detected in any of the wells [10]. It was reported that the wells were used as a source of irrigation water for paddy fields, and farmers claimed that they had to enter the wells from time to time to set up the pumping system and to carry out general maintenance (Fig. 1).
While irrigation wells are a common feature of the rural landscape in the lower north of Thailand, the survey in Kamphaengphet province [10] made no mention of why some wells presented hazardous conditions while others in the same locality did not. An understanding of the factors predisposing to hazardous conditions in shallow wells would be useful in identifying unsafe wells, and possibly in identifying ways to remediate the condition of hazardous wells. Such understanding may enable the formulation of practical recommendations or guidelines for the safe use and management of shallow wells, for dissemination among farmers and other well users.