Self-contained breathing apparatus (SCBA) are the heaviest type of respirators, and are frequently worn with firefighter turnout gear or impermeable chemical protective suits during strenuous, life-threatening conditions such as firefighting or hazardous waste cleanup. The combination of intense exertion while wearing the heavy SCBA may significantly increase cardiovascular stress. Most SCBA respirators are equipped with full face pieces made of rubber, silicone, or neoprene.
Navy and Marine Corps Public Health Center (2014). Respirator Medical Evaluation. pp.D-1 - D-12.