▁hot ▁and ▁poor ly ▁vent il ated ▁( if ▁at ▁all ). ▁Therefore , ▁use ▁is ▁usually ▁limited ▁to ▁short ▁dur ations ▁of ▁up ▁to ▁ 2 ▁hours , ▁depending ▁on ▁the ▁difficulty ▁of ▁the ▁work . ▁Level ▁A ▁( Un ited ▁States ) ▁su its , ▁for ▁example , ▁are ▁limited ▁by ▁their ▁air ▁supply ▁to ▁around ▁ 1 5 – 2 0 ▁minutes ▁of ▁very ▁str enu ous ▁work ▁( such ▁as ▁a ▁fire f ight ing ▁rescue ▁in ▁a ▁building ). ▁However , ▁OS HA / E PA ▁protect ive ▁level ▁A ▁su its / ens emb les ▁are ▁not ▁typically ▁used ▁in ▁fire f ight ing ▁rescue , ▁especially ▁during ▁a ▁building / structure ▁fire . ▁National ▁Fire ▁Prote ction ▁Association ▁( NF PA ) ▁comp li ant ▁" turn out ▁g ear ", ▁and ▁N IOS H - cert ified ▁SC BA , ▁or ▁C BR N ▁SC BA , ▁are ▁the ▁primary ▁protection ▁techn ologies ▁for ▁structure ▁fire f ight ing ▁in ▁the ▁US . ▁ ▁Rat ings ▁ ▁In ▁the ▁United ▁States ▁ ▁Haz mat ▁protect ive ▁cl othing ▁is ▁class ified ▁as ▁any ▁of ▁Level ▁A , ▁B , ▁C , ▁or ▁D , ▁based ▁upon ▁the ▁degree ▁of ▁protection ▁they ▁provide . ▁ ▁Level ▁A ▁The ▁highest ▁level ▁of ▁protection ▁against ▁v ap ors , ▁g ases , ▁m ists , ▁and ▁particles ▁is ▁Level ▁A , ▁which ▁consists ▁of ▁a ▁fully ▁enc aps ulating ▁chemical ▁entry ▁suit ▁with ▁a ▁full - face pie