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Flammable Materials

LEL – Lower Explosive Limit. UEL – Upper Explosive Limit, PPM – Parts per Million, Density (lighter than air, heavier than air)

These terms provide a starting point to understanding hazard management around explosive and flammable materials. Beyond the common flammable liquids like gasoline and diesel fuel, liquid propane and compressed natural gas, there are dozens of other flammable materials available and in use by industry every day.

Life Safety and Hazardous Material Emergency Alarm Systems provide the first warning and the last line of defense around these dangerous flammable materials.  They operate by sensing at extremely low levels and then activating ventilation controls, material shutoffs and other mitigation steps to limit the danger.


Hydrocarbon Fumes

Hydrocarbon fumes are the products of the vaporization of gasoline and a variety of other petroleum liquids and can also be created during many industrial processes.  Hydrocarbon liquids routinely evolve vapors at room temperature.  Hydrocarbon fumes are heavier than air and usually have a strong odor commonly associated with gasoline.   Swallowing or inhaling hydrocarbons can cause lung irritation, with coughing, choking, shortness of breath, and neurologic problems. Excessive exposure can cause irregular heartbeats, rapid heart rate, or sudden death, particularly after exertion or stress.

Hydrocarbon fumes can be a danger in many fueling operations. All facilities where Hydrocarbon fumes can be generated should be ventilated to manage this flammability hazard.  If the areas cannot be ventilated, special electrical equipment must be provided to eliminate arcing.  The hazards and expenses associated with hydrocarbon fumes can be reduced through installation of a gas leak detection and mitigation system.


Liquid Petroleum Gas

Liquid Petroleum Gas is a blend of the common hydrocarbons butane and propane.

Used as early as 1860, it is now used for heating homes, fueling vehicles, and a number of industrial processes.  It is heavier than air and highly flammable.   Today, LPG may also contain ethane and ethylene as well as a mercaptan, an odorant added as a safety precaution. LPG fumes can be a danger in fueling operations and industrial processes.  All facilities where LPG fumes can be generated should be ventilated to manage this flammability hazard and special electrical equipment may be required to prevent accidental explosion.  Gas leak detection is key to reducing the potential for explosion and fire hazards and expenses associated with an LPG fueling, use or storage system.


Compressed Natural Gas

Compressed Natural Gas is primarily pressurized methane.  Lighter-than-air, odorless, colorless, tasteless and highly flammable, CNG will not pool as a liquid or vapor. Nevertheless, indoor leaks can form a flammable mixture in the vicinity of an ignition source.

Drawn from natural gas wells and in conjunction with crude oil production, it is used for heating homes, as a vehicle fuel, and in industrial applications. Worldwide, CNG is powering over 12 million vehicles on the road today.  In the U.S, there are approximately 250,000 CNG vehicles on the road almost exclusively in trucks and busses.  As a vehicle fuel, CNG costs less than gasoline or diesel and emits 90% fewer emissions than gasoline when burned. It is critical to protect employees and equipment from CNG hazards during any process with the potential for a CNG release.



Hydrogen is the most abundant chemical in the universe! Hydrogen is odorless, colorless, tasteless, non-toxic, and lighter than air.  Hydrogen is an emerging vehicle fuel and is used for a variety of industrial purposes.  It is highly flammable and burns with a flame that is invisible.   Because hydrogen is a very light gas, it has the potential to quickly disburse.  It can be safety handled in very well ventilated areas.  When hydrogen is created or used in areas with little or no ventilation, it can create flammable conditions without any odor or visual indication.  Any process with the potential to release hydrogen into a confined, unventilated,  location should carefully consider this gas’s hazards.



Acetylene is an odorless, colorless gas with a density close to the density of air.  It is extremely flammable and explosive.  It is unique in that it is flammable across a wide range of concentrations in air. Acetylene is the most common gas used for fueling cutting torches in both general industry and the mining industry and as a hardening reactant in metal hardening applications.   When mixed with pure oxygen in a cutting torch assembly, an acetylene flame can theoretically reach over 5700°F. Users of this type of equipment are generally familiar with the fire hazards associated hot flames and the production of hot slag. However, many users may not be aware of the unique characteristics of acetylene itself that create special hazards compared to other fuel gases. The unstable chemical properties of acetylene gas make it very sensitive to conditions such as excess pressure, excess temperature, static electricity, or mechanical shock.  For these reasons, as well as its wide range of flammability, any process or location where acetylene is used must be carefully evaluated to minimize or eliminate the hazards.


Ethylene Oxide

Ethylene oxide (EtO) is a colorless gas with an ether-like odor.  This gas is highly explosive and reactive. It is a very common industrial chemical and it is one of the 25 highest-production chemicals (by volume) in the United States.  It is the key ingredient in automotive antifreeze.  It is used in the production of soaps and other cleaning products and has common usage for fumigation and sterilization.   Because of its diverse role as a common chemical ingredient, it is found in many chemical manufacturing locations.  Acute exposures to EtO gas may result in respiratory irritation and lung injury, headache, nausea, vomiting, diarrhea, shortness of breath, and cyanosis. Chronic exposure has been associated with the occurrence of cancer, reproductive effects, mutagenic changes, neurotoxicity, and sensitization.



Ethanol is a clear, colorless and flammable liquid.  It has bactericidal activity and is used often as a topical disinfectant. It is widely used as a solvent and preservative in pharmaceutical preparations as well as serving as the primary ingredient in alcoholic beverages. Ethanol has widespread use as a solvent of substances intended for human contact or consumption, including scents, flavorings, colorings, and medicines. When incorporated in alcoholic beverages, ethanol has a depressive effect on the central nervous system and because of its psychoactive effects; government health professionals consider it a drug.  Industrial uses include agricultural chemicals, dyes, fillers, fuel and fuel additives.  Consumer uses include Anti-freeze and de-ice products, cleaning supplies, food packaging, inks, toner, paints and coatings.  Ethanol can have flammable vapors.  Ingestion can cause a burning sensation, headache, confusion, dizziness, and unconsciousness.



Toluene is a clear, colorless liquid widely used as an industrial solvent.  It is an aromatic hydrocarbon with the typical smell of paint thinners.   Toluene is also added to gasoline and used to produce benzene. Exposure to toluene may occur from breathing ambient or indoor air affected by such sources. The central nervous system is the primary target for toluene toxicity in both humans and animals for acute (short-term) and chronic (long-term) exposures. Central Nervous System dysfunction and narcosis have been observed in humans acutely exposed to elevated airborne levels of toluene; symptoms include fatigue, sleepiness, headaches, and nausea. The gas is also irritating to the eyes and the respiratory tract.  The vapors from toluene mix very well with air and explosive mixtures are easily formed. Any person working with toluene should be trained to be aware of its’ hazardous properties.



Benzene is a clear, colorless to light yellow liquid at room temperature.  It is toxic, volatile and flammable.  Derived as a byproduct of coal distillation, benzene is a common solvent in paints, varnishes, and lacquer thinners. It is a main ingredient in gasoline and is used as an industrial chemical in many processes.  It can be released into indoor air as a liquid spray, mist, or vapor.   When it is in gaseous form it has a sweet aromatic, gasoline-like odor.  The odor threshold generally can provide adequate warning for acutely hazardous exposure concentrations. Benzene exposure causes central nervous system damage acutely and is carcinogenic.