Capabilities: (1) Overview: DEA agents wearing Level B hazmat suits. The United States Department of Homeland Security defines a hazmat suit as "an overall garment worn to protect people from hazardous materials or substances, including chemicals, biological agents, or radioactive materials". More generally, Hazmat suits may provide protection from: Chemical agents through the use of appropriate barrier materials like teflon, heavy PVC or rubber and Tyvek. Nuclear agents possibly through radiation shielding in the lining, but more importantly by preventing direct contact with or inhalation of radioactive particles or gas. Biological agents through fully sealed systems often at overpressure to prevent contamination even if the suit is damaged (see Positive pressure personnel suit) or using powered air purifying respirators with full hoods and protective suits to prevent exposure (level c protection level). Fire/high temperatures usually by a combination of insulating and reflective materials which reduce the effects. The hazmat suit generally includes breathing air supplies to provide clean, uncontaminated air for the wearer. In laboratory use, clean air may be supplied through attached hoses. This air is usually pumped into the suit at positive pressure with respect to the surroundings as an additional protective measure against the introduction of dangerous agents into a potentially ruptured or leaking suit. Working in a hazmat suit is very strenuous, as the suits tend to be less flexible than conventional work garments. With the exception of laboratory versions, hazmat suits can be hot and poorly ventilated (if at all). Therefore, use is usually limited to short durations of up to 2 hours, depending on the difficulty of the work. Level A (United States) suits, for example, are limited by their air supply to around 15-20 minutes of very strenuous work (such as a firefighting rescue in a building). However, OSHA/EPA protective level A suits/ensembles are not typically used in firefighting rescue, especially during a building/structure fire. National Fire Protection Association (NFPA ) compliant "turnout gear", and NIOSH-certified SCBA, or CBRN SCBA, are the primary protection technologies for structure firefighting in the US