Hazards of Chemicals and Gases
The following discussion addresses some of the more commonly used gases, and describes the
specific chemical properties and characteristics that are important for accident prevention.
Hydrogen (H ) is the lightest of all elements. Its presence cannot be detected by any of the
senses. It is flammable in oxygen or air, and has a flammable range of from 4.1 percent to
74.2 percent by volume in air. A mixture of 10 to 65 percent hydrogen by volume in air will
explode if ignited. Pure hydrogen burns quietly in air with an almost invisible flame, and when
burned with pure oxygen, a very high temperature may be reached. Hydrogen will burn readily
in chlorine gas, and under proper conditions, will combine with nitrogen, forming ammonia.
Some chemical reactions produce hydrogen as a byproduct. A lead-acid battery will produce
hydrogen when it is being charged. Metallic sodium and potassium are examples of some
chemicals that react violently when exposed to water, producing hydrogen, which may flame
spontaneously due to the heat of the reaction. Many electroplating processes produce hydrogen.
Some chemicals used to remove scale from the water side of boilers give off hydrogen.
Whatever the operation, it is important to know whether hydrogen will be produced, and if so,
precautions must be taken to prevent its accumulation and ignition. The precautions to take
include adequate ventilation to prevent its accumulation and the elimination of possible sources
of ignition. Hydrogen is classified as an asphyxiant.
Nitrogen (N ) makes up more than 78 percent of the earth's atmosphere. It will not burn or
support combustion. It cannot be detected by any of the senses and it is not toxic. Although it
is often referred to as an inert gas because it does not oxidize readily, it nevertheless forms many
compounds. It is frequently used to inert systems that contain, or have contained, flammable
liquids or gases. Inerting a system means replacing the oxygen with an inert gas in order to
reduce the possibility of fire or explosion.
Nitrogen is fairly soluble in the blood, and a considerable amount will dissolve in the blood of
a person when the air pressure is increased, as in diving, caisson, and some tunnel work. If these
employees are not properly decompressed, the dissolved nitrogen escapes from the blood in the
form of small bubbles in the bloodstream causing intense pain and is often fatal. This disorder
is commonly known as the bends.
If a large amount of nitrogen were released into the air of an enclosed space, it could cause a
serious oxygen deficiency. Nitrogen is an asphyxiant.