31. Any combustible gases in the main exhaust should, if feasible, be kept below the LEL.  LEL means:

32. High expansion foam is used mainly to contain and control fire by removing two legs of the fire triangle — oxygen and fuel.

33. Urethane foam is an effective sealant when used around the perimeter of a seal.  Urethane foam should never be applied more than ______ thick because of the potential for spontaneous combustion with greater thicknesses.

34. Please choose the class for an electrical fire from the choices below:

35. Carbon monoxide gas will not explode.

36. The first symptom of carbon monoxide poisoning is:

37. Air locks are not required prior to opening a refuge chamber, barricade, or door in irrespirable atmospheres behind which survivors may be located.

38. Before going underground, the team should make sure that the main fan is running, that a guard is monitoring the operation of the fan, and ___________.

39. Elevated readings of ___________ could indicate that there is inadequate ventilation around battery charging stations.

40. You may recognize ___________ by its distinctive "rotten egg" odor.