Oxygen. Oxygen is nonflammable but it supports the combustion of flammable materials. It can initiate combustion and vigorously accelerate it. Therefore, oxygen cylinders and liquid oxygen containers should not be stored in the vicinity of combustibles or with cylinders of fuel gas. Oxygen should never be used as
a substitute for compressed air, for example, to power compressed air tools, because they are almost always lubricated with oil.
It is very dangerous to use oil or grease on oxygen cylinders or regulators because contact with oxygen causes oil and grease to ignite spontaneously. It is a dangerous practice to use or store oxygen cylinders where oil and oxygen will be brought together. Also, it is dangerous to attempt to use cylinders which have contained petroleum products for oxygen, because they will contain a certain amount of residual oily deposit. Only apparatus that has been manufactured expressly for oxygen service should be used, and manufacturers specifications should be followed.
Fuel gases commonly used in oxyfuel gas welding and cutting are acetylene, methyl acetylene-propadiene (MPS), natural gas, propane and propylene. Hydrogen is used in a few applications. Gasolene is sometimes used as fuel for oxygen cutting. These gases should always be referred to by the correct
name.
Acetylene. Acetylene cylinders must be handled carefully. They should never be used at pressures over 100 kPa (15 psi). If heated, the gas in the cylinder could become unstable; if shocked, an explosion could occur.
As a safety measure, the cylinders are equipped with fusible safety plugs that melt at 99°C (210°F). Therefore, if acetylene cylinders are in a fire, the safety plugs should vent the internal pressure rather than let the pressure build up and cause an explosion.
Acetylene and MPS should never be used in contact with silver, mercury, or alloys containing 70% or more copper. These gases react with these metals to form unstable compounds that may detonate under shock or heat. Valves on fuel gas cylinders should never be opened to clean the valve outlet, especially not near possible sources of flame ignition or in confined spaces.
When fuel gases are used for a brazing furnace atmosphere, they must be burned or vented to a safe location. Prior to filling a furnace or retort with fuel gas, the equipment must first be purged with a non-flammable gas, such as nitrogen or argon, to prevent formation of an explosive air-fuel mixture.
Special attention must be given when using hydrogen. Flames of hydrogen may be difficult to see and parts of the body, clothes, or combustibles may come in contact with hydrogen flames without the operator’s knowledge.
Shielding Gases. Argon, helium, nitrogen, and carbon dioxide (CO2) are used for shielding with some welding processes. All, except CO2, are used as brazing atmospheres. They are odorless and colorless and are hazardous because they can displace air needed for breathing.
Confined spaces filled with these gases must be well ventilated before personnel enter them. If there is any question, the space should be checked first for adequate oxygen concentration with an oxygen analyzer. If an analyzer is not available, an air-supplied respirator should be worn by anyone entering the space. Containers of these gases should not be stored in confined places.