Construction Health and Safety Technician (CHST) 2025 – 400 Free Practice Questions to Pass the Exam

In assessing hazardous atmospheric environments, it is crucial to understand how different factors can contribute to the danger presented in a work area. A flammable gas being present at a concentration of 25 percent of its Lower Flammable Limit (LFL) is a significant indicator of a hazardous environment. The LFL represents the lowest concentration of gas in air that can ignite and sustain combustion. When the concentration reaches 25 percent of this limit, it means there is a substantial amount of flammable gas present, which poses a serious risk of explosion or fire if an ignition source is introduced.

The scenarios involving oxygen levels below 19.5 percent or the presence of toxic gases at normal levels also indicate concerns for safety, but they do not represent the immediate and catastrophic risk associated with flammable gases at high concentrations. Temperature alone can contribute to hazards but does not directly indicate an atmospheric hazard unless combined with other factors, such as flammable materials or humidity.

Thus, a concentration of 25 percent of the LFL of a flammable gas highlights a clear and present risk for combustion, thereby categorizing it as indicative of a hazardous atmospheric environment.