Improperly compensated risk is a primary factor in many unnecessary respiratory hazard incidents. A common engineering control used for controlling respiratory hazards is a ventilation hood system or local fume mitigation vacuum. Gases with a vapor density heavier than air pose potential hazards to workers in basements and other areas such as confined spaces. Gases with a vapor density lighter than air can accumulate at the top of shafts or ceilings. Firefighters, hazardous materials teams, and other first responders rarely have the ability to measure the quantity of substance(s) in the air, so their first choice is usually the positive-pressure, self-contained breathing apparatus (SCBA). In any workplace where respirators are necessary to protect the health of the employee or whenever respirators are required by the employer, the employer shall establish and implement a written respiratory protection program with worksite-specific procedures.