Hazards of Chemicals and Gases
Liquid oxygen, or oxygen-rich air atmospheres, should not come in contact with organic
materials or flammable substances. Some organic materials (oil, asphalt, kerosene, cloth, or dirt
containing oil or grease) react violently with oxygen, and may be ignited by a hot spark. Liquid
oxygen may form mixtures that are shock sensitive with fuels, oils, or grease. If liquid oxygen
spills on asphalt, or on another surface contaminated with combustibles (for example, oil-soaked
concrete or gravel), no one should walk on, and no equipment should pass over, the area for at
least 30 minutes after all frost or fog has disappeared.
Any clothing that has been splashed or soaked with liquid oxygen, or exposed to a high
gaseous-oxygen atmosphere, should be changed immediately. The contaminated systems should
be aired for at least an hour so that they are completely free of excess oxygen. Workers exposed
to high-oxygen atmospheres should leave the area and avoid all sources of ignition until the
clothing and the exposed area have been completely ventilated. Clothing saturated with oxygen
is readily ignitable and will burn vigorously.
Specific Properties of Selected Industrial Gases
Anyone who uses gases must have a thorough knowledge of their chemical properties to
maintain a controlled operation. If the gas is flammable, its flammable range and ignition
temperature must be known.
The lower flammable limit is the smallest percent of the gas in air which can ignite when exposed
to the ignition temperature. The upper flammable limit is the point above which the mixture is
too rich in fuel to ignite. The range between these two limits is the flammable, or explosive,
range. The most violent explosion will occur at concentrations about the middle of the
flammable range. Sources of heat that may cause temperatures that exceed the ignition
temperature must be avoided, as well as gas-air mixtures that are within the flammable range.
The physiological effects of the gas must be known, not only types of reactions, but also severity
of reactions. All employees who handle gas should be familiar with its effects, and recommended
The chemical reactivity of the gas must be known. This includes a knowledge of the materials
that are resistant to its chemical effects, the materials with which it reacts, and how it reacts with
such materials. Some gases become unstable at high pressures, and others become more
corrosive at high temperatures.
The term Threshold Limit Value (TLV) is sometimes used and is defined as: The highest
time-weighted average concentration of an air contaminant which if breathed for a normal
working day is unlikely to result in health injury to the average person, either at the time, or after
years of exposure.