1. Why is it essential that volcanologists use self-contained breathing apparatus when conducting studies involving active volcanoes?

2. Is there a danger of fire and explosion within a segment of a sanitary sewer in which the hydrogen sulfide concentration measures 2.5% by volume in the surrounding air?

3. Why do safety experts recommend separating nitric oxide cylinders from flammable gas cylinders during their storage by a minimum distance of 20 feet (6.1 m or by a barrier of noncombustible material at least 5 feet (1.5 m) high, having a fire resistance rating of at least hour?

4. Although ammonia has a vapor density of 0.6 (air = 1), why does released ammonia sometimes linger near the surface of the ground rather than rising into the air and dispersing?

5. Why do experts advise emergency responders to remove contaminated clothing a wash their skin when they have been exposed to dispersing?