Preplanning Gases at Industrial Sites


Understanding the hazards that await you at industrial sites is part of preincident preparedness. What fire officers know before an emergency allows them to be better prepared. By obtaining essential information and conducting training on site-specific hazards and determining resource needs and their procurement, fire department leaders increase the chances of a successful outcome and firefighter survival. Preparedness efforts, however, should not focus solely on target hazards that present obvious operational challenges.

Firefighters may perceive certain occupancies as low hazard or low risk. This perception can lead to complacency, with the result that preparedness efforts are often overlooked. Every facility you protect can hurt you; every facility provides a challenge. Recognizing those challenges is critical to a successful outcome. Certain occupancy classifications, such as a business setting, likely would be considered a low hazard. However, it is important to remember that low hazard does not mean no hazard.


When I teach hazardous materials operational programs, an exercise includes students’ identifying hazardous materials locations. They often stereotype specific local facilities and general industrial types. When specific materials are mentioned, the occupancy types expand. Occupancy type, for example, is not the only indicator of propane: Propane can be found in local mini-marts, some of which provide a propane cylinder exchange program; storage facilities; and residential occupancies. The fact that the presence (use) of hazardous materials is widespread must be reinforced. Identify the facilities in your jurisdiction that use, store, or manufacture hazardous materials. Don’t think that dangers await you only in certain occupancy types.

(1) This portable cryogenic cylinder is in a valve manufacturing facility. Note the wheeled cart, which allows the container to be moved throughout the facility. (Photos by author.)
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Hazardous materials, regardless of their state, present challenges. The fire service is generally well acquainted with the locations of flammable and combustible liquids. The characteristics of compressed gases, however, differ. The use of compressed gas may not be obvious in some occupancies, and their presence during an emergency may significantly alter incident circumstances, strategies, and tactics.

The intent of this article is not to provide mitigation techniques for compressed-gas emergencies or review cylinder components and construction. Those competencies are beyond the scope of hazardous materials operations-level training as defined in the Occupational Safety and Health Administration (OSHA) 49 Code of Federal Regulations section 1910.120, which is the level to which most firefighters are trained. The purposes of this article are to broaden your focus when gathering preincident information and to alert you to the fact that you would be surprised at some of the occupancy types where gases are employed.


Differentiating among the basic hazard classifications of gases is important for improving your effectiveness and safety on the fireground. Of the nine hazard classes established by the United States Department of Transportation, gases are Hazard Class 2. They are subdivided into three categories: flammable, nonflammable, and poisonous.

Hazard Class 2.1: Flammable

A material is considered a flammable gas when its lower explosive limit (LEL) is 13 percent concentration by volume in air or lower. Common flammable gases include acetylene, hydrogen, propane, and methane.

Hazard Class 2.2: Nonflammable

A grave misunderstanding relative to this subdivision is the assumption that it does not pose a fire hazard because of the nonflammable designation and the inherent green color of the placard. Some gases in this subdivision, however, have a flammable range (FR) and can ignite and sustain a fire. Some nonflammable gases have an LEL. However, in the nonflammable category, a material must have an LEL above 13 percent volume in air. Anhydrous ammonia, for example, has an LEL of 16 percent and will become explosive when it reaches that concentration in air. Other examples of nonflammable gases include carbon dioxide and nitrous oxide.

Hazard Class 2.3: Poisonous

These materials are toxic based on lethal concentration values revealed through laboratory testing. Chlorine and phosgene are examples of poisonous gases. These gases may present other hazards.

Depending on the information source, the hazard classes of the materials listed above may vary. Generally in transportation, however, the classes for the materials listed above are accurate.


Materials within the above hazard classes can further be categorized into four listings. Aspects, such as atmospheric conditions, may affect one material and not another. This must be a consideration during operations.

Liquefied and compressed gases are categorized as follows:

  • A nonliquefied compressed gas is a material that is a gas at 68°F and is packaged within a container under pressure. Examples include oxygen, helium, and nitrogen.
  • A liquefied gas is a material that exists partially as a liquid at 68°F and is packaged within a container under pressure. Examples are ethylene oxide and liquefied petroleum gas (LPG).
  • Acompressed gas in solution, also referred to as a dissolved gas, is a nonliquefied compressed gas that is dissolved in a solvent. Acetylene, for example, is very unstable in itself and is dissolved in acetone to stabilize it.
  • A cryogenic liquid is a refrigerated liquid that has a boiling point of less than –130°F. Examples of cryogenics include liquid oxygen and liquid nitrogen.

Atmospheric conditions may influence these materials and their containers. For compressed gases, temperature changes usually have minor effects on the cylinder’s pressure. Liquefied gases may be significantly affected by temperature change.

For the purposes of this article, the term “compressed gases” includes all of the above categories.


Compressed gases have varying behaviors; it is essential to distinguish among them. Flammability and nonflammable attributes are critical factors during incident operations. Asphyxiation hazards are also common; they can displace oxygen, which can have quick and undetected effects. Common cryogenic physical hazards include thermal burns, such as frostbite.

Detecting released gases can be difficult. Many are odorless, colorless, and tasteless. Never rely on an individual’s sense of smell to detect or verify a gas release. A person can unknowingly be desensitized to a material, resulting in injury or death. Do not attempt to detect or verify a gas release without an air monitor. Some specific physical characteristics must be known beforehand. Vapor density (VD) is the weight of a gas in comparison to air. Air is designated a VD of 1.0. A gas with a VD lower than 1.0 will rise; a gas with a VD higher than 1.0 will stay low. This fact, coupled with other material-specific characteristics, could pose an increased risk for responders.


Several chemical hazards are associated with compressed gases. They may be corrosive. Corrosiveness is measured on a scale of 0 to 14, 7 being neutral. Acidic gases have a pH of less than 7; basic or alkaline gases, higher than 7. Reactivity can also create hazards. It is important to know which materials will cause reactivity. For example, acid and base gases may react, and oxidizing gases can react with fuels. Toxicity generally is measured in parts per million (ppm) or parts per billion (ppb) for inhalation exposures.

It is difficult for most firefighters to determine chemical hazards. Special detection devices, which may not be available in the fire departments, are needed. You have to know the chemical hazards associated with compressed gases to avoid exposure, which is primarily through inhalation, absorption, and direct skin contact. (Troubleshooting compressed gas cylinder problems and mitigation practices such as repair, containment, transfer, and disposal of compressed gases are beyond the scope of this article.)


Compressed gases generally are stored in low- [less than 900 pounds per square inch (psi)] or high-pressure cylinders (900 or greater psi). The lethality of a pressure blast can be realized at as low as 8 to 10 psi. Glass will shatter between 0.5 and 1 psi. Eardrum rupture can be expected at 2 to 3 psi. A wooden utility pole may snap at 5 psi. Pressure blast damage may be relative to the size of the cylinder as well. However, from a personal injury standpoint, it really does not matter if you are near a low- or a high-pressure cylinder when it fails.


Compressed gases are used in many settings. Regardless of whether it is a residential, a commercial, or an industrial establishment, you must identify and be familiar with the materials you might encounter. Several of the gases most commonly encountered are described below.

  • Acetylene, designated as a flammable gas, is commonly used in oxyacetylene welding operations. It may be encountered in a wide spectrum of occupancies, including a large metal processing facility, a vehicle body repair shop, and facility maintenance areas of all sizes and types. Its vapor density is 0.9; it is slightly lighter than air and will rise. It is colorless and generally odorless; however, commercial grade acetylene may have a garlic-like odor. Its FR is between 2.5 and 80 percent. It is primarily a fire hazard but also can act as an asphyxiant.
  • Argon, a nonflammable gas, is an inert gas, meaning that it is basically nonreactive. It is commonly found in the filling of incandescent and fluorescent lamps and electronic tubes. It is used as a refrigerant liquid and is generally stored in a cryogenic cylinder. It has a vapor density of 1.38, which indicates it is heavier than air. It is colorless, odorless, and tasteless and can create oxygen-deficient atmospheres. Inhalation symptoms include dizziness, nausea, confusion, vomiting, and loss of consciousness. Liquid exposure, or direct skin contact, can cause extensive tissue damage and burns.
  • Carbon dioxide (co2), with a vapor density of 1.5, is listed as a nonflammable gas. It can be used as a cooling agent in heat-sensitive industries, is commonly used for carbonation of soft drinks, and is also used for fire suppression. It is colorless and odorless but may have a pungent odor or biting taste. It will not burn or support combustion. Exposure to co2 can affect the heart rate and cause labored breathing. Other exposure symptoms include headache and dizziness. A 10 percent concentration can cause unconsciousness.
  • Chlorine, a nonflammable poison gas, is widely used in the water-treatment industry, in the manufacturing of pesticides and herbicides, and as a bleaching agent in the paper and flour industries. Since it has a vapor density of 2.4, a release of gas will follow the terrain. Chlorine gas is greenish yellow and has a pungent odor. Although considered nonflammable, it can support combustion of certain substances and may react explosively with organic materials. Another consideration is the formation of a weak hydrochloric acid solution when mixed with water.

(2) These one-ton containers of chlorine are used in this water-treatment facility.
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  • Ethylene oxide is flammable, and its vapors can be explosive. It is used in the manufacturing of ethylene glycol (antifreeze) and can be used as a fumigant and a sterilant. It is also used as a drying and ripening agent in the produce industry. It is 1.5 times heavier than air with its flammable vapors. Its flammable range is between three and 100 percent. It is colorless, odorless, and tasteless. Exposure can have mutagenic effects, as revealed in laboratory testing, and is a suspected carcinogen. It can initially be an irritant to the respiratory system and cause headaches, nausea, and vomiting.
  • Helium, the second lightest of all elements, is a nonflammable gas. It is colorless, tasteless, and odorless. Commonly used cryogenically as a refrigerant in research laboratories, it also has other applications in the heat-treating, metal-processing, and glass-manufacturing industries. It is also used in florists, specialty gift-card shops, and other stores that sell helium balloons. Significantly lighter than air, helium is nontoxic, but it can act as an asphyxiant and can cause dizziness, nausea, vomiting, and loss of consciousness and possibly result in death

(3) Helium cylinders are used to fill balloons, which are sold in many types of occupancies in many communities.
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  • Hydrogen is an extremely flammable gas. The lightest of all elements, it is widely used in the petrochemical, hydro-treating, heat-treating, metal-processing, welding, and cutting industries. Its vapor density is less than 1; it is colorless, tasteless, and odorless. Like helium, it is nontoxic and can result in an oxygen-deficient atmosphere. Inhalation can result in unconsciousness without warning. Liquid hydrogen exposure can produce severe cryogenic burns. Hydrogen has an FR of between four and 75 percent in air. When burning, the flame is pale blue and virtually invisible. Although you would be able to feel the heat, it would be difficult to locate the fire. The 2004 North American Emergency Response Guidebook suggests using a wooden broom handle to locate the fire

(4) A fixed hydrogen rack outside a facility that manufactures electronic cooling mediums. Note the proximity to the building as well as the wall vents behind the rack, which could facilitate the entry of the gas if there is a release.
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  • Liquefied petroleum gas (LPG) consists of a propane-butane mixture, but it can also contain small percentages of ethane, ethylene, propylene, isobutene, or butylenes. It is used in a variety of domestic, industrial, and commercial uses. Don’t be surprised at where you may find it. Its VD is 1.5 times that of air. Released propane will remain low; it has an FR of between 2.2 and 9.5 percent. Propane is primarily a fire hazard, but it can have anesthetic effects resulting from oxygen displacement.

Although the individual properties and characteristics of butane and propane are comparable, they are different compounds. Their VDs are similar; butane’s VD is 2.1. As in the case of propane, this will cause butane to sink. Butane also has a relatively narrow flammable range and has an LEL of 1.6 percent and a UEL of 8.4 percent.

Another distinct property that can have great influence at an incident is the boiling point (BP). Propane has a BP of –44°F. This means that in most areas, except for very extreme cold-weather climates, propane will be in a gaseous state when released from its container. Butane’s BP, on the other hand, is 31°F, and climate may play a significant role in its volatility during an incident.

All physical properties and conditions, chemical and incident, require consistent consideration during the life of the incident. Changing conditions, such as temperature, may change the hazard risk. An early-morning incident involving butane at 0200 hours at temperatures well below 30°F may be deemed a low-fire risk because the product is below its BP. However, as the incident progresses and temperatures increase to or above the BP, so does its vapor production. The container stressor may have weakened its integrity, and an increase of vapor pressure, even if not obvious, could cause container failure.

The uses of propane and butane are many; they include domestic, industrial, horticulture, and agriculture. Although their use in bulk is typically considered, do not discount smaller container applications. They are also used as an aerosol propellant, replacing fluorocarbons that cause deterioration of the earth’s ozone layer.

  • Nitrogen is a nonflammable gas with a specific gravity of 0.967. It has widespread applications and is commonly used in the heat treating of metals as well as a freezing agent. It can cause asphyxiation through displacement of oxygen. Dermal exposure to liquid nitrogen can cause frostbite.
  • Nitrous oxide, a nonflammable gas, is heavier than air and has a VD of 1.5. It is colorless and has a slight sweet odor and taste. Even though it is nonflammable, it will accelerate the burning of combustible materials. It is commonly used as an anesthetic in large medical facilities and certain family medical practices and other outpatient facilities. It is used as a pressure propellant in aerosol cans and also as a fuel oxidizer for racing.

(5) This oral surgery facility uses nitrous oxide as an anesthetic for outpatient surgeries.
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Nitrous oxide has long-term exposure side effects as well as feto-toxic effects that can result in spontaneous abortion. It is important to keep this material away from oils, grease, and other combustible materials. Exposure to fire could result in a violent reaction.


Compressed gas containers may be fixed or portable and may be stored away from an exposure or next to an exposure, or they can become an exposure. Usually, if cylinders are stored outside a structure, there are cylinders inside as well. When preparing preplans, do not fail to list the potential for interior compressed gas cylinder storage and use. Often, only the designated storage locations are listed and marked on maps; all use areas are not indicated.

(6) This CO2 cylinder is stored in the storeroom of this pizzeria. It is in the back hallway, unsecured, and, as you can see, serves double duty as a coatrack. What could happen during search and rescue efforts? Could the cylinder be knocked over? What would happen if the valve stem were damaged and caused a release?
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It is necessary to know how the presence of compressed gas units may compound a situation—the impact of a structure fire’s breaking out of the windows when cylinders are outside, for example. Also, note that usually various electrical components, including air-conditioning units, are below the cylinders. How would the cylinders be affected when exposed to a fire in one of these units? Do not list only the buildings when identifying exposures.

(7) Cylinders and tanks may not be labeled, as in the case of this ammonia tank.
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Some facilities may not employ the best of storage practices. Whether right, wrong, or indifferent—or if in violation of storage practices—you must know what to expect. Cylinders may be positioned anywhere—in corners, in closets, and in the middle of a pathway, for example.

A facility may also employ an exterior bulk storage arrangement with the compressed or liquefied gas piped into a facility. It is important to recognize the location of compressed gas cylinder/tanks. A building previously used for general storage recently was renovated into a cold storage warehouse. Anhydrous ammonia is used as a refrigerant at this site. The ammonia tank was installed on the facility’s roof along with a cooling unit. You must determine what’s in cylinders and tanks. They may not be labeled.

(8) A cylinder storage area. Note the varying cylinder and cylinder cap colors. They may have certain meaning to the facility, but there is no industrywide coloring practice.
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Another storage misconception is related to cylinder color. There is no standard for the coloring of compressed gas cylinders; do not use color as the basis for identifying products. Some facilities may have their own internal cylinder color references. Do not rely on assumptions pertaining to cylinder product. As noted earlier, compressed gases do not have the same properties. Assuming, based on container color, that a certain gas is involved may have detrimental consequences.


How accessible are the cylinders? You must consider security in your preplans. Someone with intentions to harm may have quick and undetected access. In some cases, I can just walk up to a tank and take a photo. Although in most cases the fire service has little control or influence on these storage practices, you must be aware of the possibility that these materials may be moved around regularly.


Incidents involving compressed gases can present precarious circumstances. This article did not address cylinder rupture; boiling-liquid, expanding-vapor explosions (BLEVEs); or compressed liquefied gas transportation issues. Odor thresholds and olfactory senses also were not discussed. Many of the materials highlighted are odorless. Odor thresholds do not apply to them. Note also that olfactory senses are individual specific; not all people have the same sense ability.

My objective is to get you to further research the characteristics of compressed gases in your area and understand their properties and how they may alter an emergency situation, your operational strategies, and your tactics. Compressed gas is widely used in virtually all areas, and it is imperative that you determine its location, which can be in many kinds of occupancies. The only way to do this is through aggressive preincident preparedness practices. You need to know what may harm your personnel—and they deserve to know. You cannot prepare yourself if you do not know what lies ahead.

ERIC G. BACHMAN, CFPS, a 26-year veteran of the fire service, is the former chief of the Eden Volunteer Fire/Rescue Department in Lancaster County, Pennsylvania. He is the hazardous materials administrator for the County of Lancaster Emergency Management Agency and serves on the Local Emergency Planning Committee of Lancaster County. He is registered with the National Board on Fire Service Professional Qualifications as a fire officer IV, fire instructor II, hazardous materials technician, and hazardous materials incident commander. He has an associate’s degree in fire science and earned professional certification in emergency management through the state of Pennsylvania. He is also a volunteer firefighter with the West Hempfield (PA) Fire & Rescue Co.

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