What Does Combustible Gas Mean?
Combustible gases are any type of gas that can potentially ignite when mixed with oxygen or an oxidizing agent. In the context of occupational safety and the use of hazardous materials (HAZMAT), an oxidizing agent is a material that can cause or enhance the combustion of another material, usually by yielding oxygen.
Combustible gases are typically made of hydrocarbons, carbon monoxide, hydrogen, or a combination of them. Butane, propane, ethane, and methane are common hydrocarbon-based combustible gases used in a variety of occupational settings.
Safeopedia Explains Combustible Gas
The dangers associated with combustible gas are severe. Unwanted or uncontrolled combustion can lead to fatal harm as a result of burns due to fire or injury due to explosion.
In addition to the immediate danger posed by a combusting gas, the potential for the combustion to ignite other flammable materials, damage safety equipment, or create hazardous flying debris all pose significant secondary risks. As such, the physical properties of a gas do not entirely define how hazardous it is - the nature of the environment that the gas is being used in, and the hazards associated with that environment, are also relevant factors.
Due to their common use in a variety of industrial settings, combustible gasses pose a danger to a variety of occupations. These include petrochemical industries, mining, and other types of enclosed space work, as well as many warehouse settings in which fuel is present. Certain settings that store significant amounts of pure oxygen, such as hospitals, may also have combustible gas concerns, as high volumes of pure oxygen can create combustion hazards in otherwise safe environments.
Combustible Gas Regulations
Employers operating facilities that use combustible gas are subject to numerous regulatory requirements. Many of these regulations are directly concerned with ensuring that the gases are safely stored, handled, and transported. However, other combustible gas regulations are chiefly concerned with avoiding ignition sources. For example, OSHA standard 1910.307 - Hazardous (Classified) Locations is concerned with ensuring that electrical equipment does not pose an ignition hazard in areas with combustible gases or other combustible materials.
Transportation regulators also play a large role in governing how hazardous materials are used and handled, and this includes combustible gases and oxidizers. Industry-specific agencies, such as the Mine Safety and Health Administration, may provide additional obligations and requirements in their specific areas of interest.
Assessing Combustible Gas Hazards
The dangers that are directly associated with a given combustible gas can be understood by assessing a number of its physical properties.
The flash point is the lowest temperature at which a specific non-gaseous solid or liquid substance will give off sufficient amounts of vapor to create a combustion hazard at the surface of the substance. A vapor is the gaseous form of a substance emitted by a volatile liquid or solid, such as gasoline.
The explosive range of a combustible gas is the range of concentrations (measured as a percentage of volume in air) at which a gas will ignite or explode when exposed to an ignition source. The explosive range is defined by two boundaries: the lower explosive/flammability limit (LEL/LFL) and the upper explosive/flammability limit (UEL/UFL).
If the concentration of a combustible gas in the air is below the LEL, then the air is considered too “lean” to burn. If the concentration is above the UEL, there will not be enough oxygen to sustain the combustion. In order to understand the level of hazard associated with a given occupational setting, it is vital to know the LEL and UEL of a gas and to be able to monitor the air in order to ensure that the concentration remains outside of the explosive range.
In the United States, OSHA’s combustible gas regulations rely heavily on the explosive range to define workplace safety obligations. For instance, standard 1910.146 - Permit Confined Spaces classifies any confined space in which a combustible gas is present at a concentration of at least 10% of its LEL as being a hazardous atmosphere.
Vapor density is the relative weight of a vapor in comparison to ordinary air. If a vapor is heavier than air, it may “spill” into low-lying areas and accumulate over time. This is why explosive gases can be a significant hazard in mines, sewers, and other underground spaces.
Auto-ignition temperature is the temperature at which a combustible gas will ignite without exposure to an outside ignition source. This is sometimes referred to as the spontaneous ignition temperature (SIT), and is of chief concern in high-heat environments.