Safety - Field Sampling: Principles and Practices in Environmental Analysis - page 90

the tank turns into a missile capable of penetrating cement block walls. For this reason
protective caps are placed on the tank during storage and transport. The tanks are secured
to some substantial cart or building structure when in use. Some gases, such as acetylene,
can ignite when escaping from a metal orifice and thus are of particular concern.
Acetylene and propane escaping from a tank can produce a flammable and potentially
explosive situation. Oxygen supports combustion, which means that both escaping
oxygen or oxygen-rich environments will support oxidation and burning where otherwise
it might not occur. Even inert gases such as nitrogen and helium can produce dangerous
situations. When released in large volumes these gases can replace all the oxygen in an
enclosed area, causing suffixation. Compressed gas tanks encountered during field
sampling must be treated with extreme caution.
Some gases, including those discussed above, are commonly liquefied under pressure
and are stored and transported in this form. Some are kept in insulated containers, while
others are in simple pressure tanks. These liquefied gases pose some of the same risks as
compressed gases in cylinders, and although they are not commonly under as much
pressure as compressed gas, dangerous leaks can develop in the tanks and cause serious
safety risks. A different hazard occurs when these liquids are spilled. One mole of liquid
nitrogen, 14 g, will occupy a volume of 22.4 liters when it warms up and becomes a gas.
The liquid can rapidly change to a gas, replacing oxygen and suffocating any people and
animals present.
In some cases liquefied gases are a fire hazard, and some are toxic or otherwise
hazardous. Flammable gases are colorless and must build up to a certain level before they
can burn or more likely explode. Liquid propane will be converted to a gas when pressure
is released and it will produce an explosive mixture with air. Unfortunately once these
gases start burning, the fire is hard to put out. Liquid ammonia will become a cloud of
ammonia gas, which is choking and toxic and will overcome a person trapped in the
cloud. All visible gases—that is, gases that have color—are toxic; however, the reverse is
not true. Many colorless gases can be toxic, however.
Fumes originating from a monitoring well can also be dangerous. They may be toxic or
flammable, and so appropriate precautions must be taken at all times when opening a
monitoring well.
4.5.2. Liquids
Liquids can either be pure organic liquids, mixtures of organic liquids, inorganic liquids,
and solutions of organic and inorganic compounds in water. These liquids may be volatile
or nonvolatile, and can release strong fumes and/or be caustic. Volatile liquids can fill an
area with fumes that can burn. In this case the fire will be fed from the pool of liquid, and
so covering the pool with an appropriate flame extinguisher can stop the fire.
Fumes originating from a volatile liquid are heaver than air and can fill and travel
through low areas. If they contact a source of ignition, the flame can travel back to the
source of the fumes and cause a large fire or explosion. When confined in a small space
they can cause the suffocation of persons entering these spaces.
Many liquids present hazards of other types. Acids and bases frequently come as
solutions of gases in water. Most common are the mineral acids—hydrochloric, nitric,