Chemical Data Notebook Series #20:

Anyone who’s taken high school biology or spent time at a funeral parlor knows the smell of formaldehyde. But the gas’s irritating odor could prove to be a lifesaver, a warning of the serious health hazards of extended exposure to the substance when firefighters confront a spill or fire.

Formaldehyde is usually shipped as a 30 to 50 percent solution in water, called formalin. Its best-known use is as an embalming fluid. Among the other products in which the gas is used are adhesives, cosmetics, deodorants, detergents, dyes, explosives, disinfectants, fungicides, paints, paper, pharmaceuticals, and textiles. An estimated eight billion pounds of formaldehyde are used in the ~ United States each year.

Formaldehyde, a suspected human carcinogen, is flammable as a gas, combustible as a solution, polymerizable, and colorless.

The gas has an ignition temperature of 806° F. It has a wide flammable range of 7 to 73 percent, and that makes it very dangerous as a fire hazard. The water solution, formalin, will have varying flash points due to the varying concentrations of formaldehyde in the water. A flash point of 122° F has been reported for the 37 percent solution, and this is the origin of the combustible liquid designation that the U.S. Department of Transportation has given the solution form of the substance.

Formaldehyde’s molecular weight is 30, and its vapor density is 1.03. Formalin has a specific gravity of 1.1. The gas boils at -2.2° F and freezes at -180.4° F. The most common solution of formalin boils at 206° F. Formaldehyde’s chemical formula is CH2O, sometimes written as HCHO.

Formaldehyde is stable, and though it’s readily soluble in water, there’s no reaction with water. The substance does react with strong oxidizers, strong alkalies, and inorganic acids, as well as with anhydrides, aniline, ammonia, isocyanates, phenols, urea, bisulfites, copper, iron and silver salts, iron compounds, and gelatin.

The gas is a monomer; when its molecules react with each other, they produce acetal, a very tough polymer. Formaldehyde can liberate large amounts of heat energy during polymerization. In a reactor vessel, this reaction is controlled, and the heat is removed in an orderly fashion. But in an uncontrolled, or runaway, polymerization, enough heat can be generated to increase pressure within the container beyond its design strength, causing catastrophic failure. The formaldehyde released may then ignite, forming a huge fireball. This pressure-relief explosion, followed instantaneously by a rapid oxidation explosion, can resemble a BLEVE (boiling-liquid, expanding-vapor explosion), and can be just as deadly.

Formaldehyde’s relatively low ignition temperature and wide flammable range make it extremely flammable in a gaseous state. Any accumulation, therefore, will produce a strong explosion when ignited.

Health hazard

As for health effects, formaldehyde has produced tumors in certain rats and mice in exposure experiments, and thus it must be treated as a substance suspected of causing cancer in humans.






Formalin 40


Formic aldehyde








Methyl aldehyde

Methylene glycol

Methylene oxide







Polyoxylene glycol

Resource Conservation and

Recovery Waste Act

Number U122


It can be detected by odor at about 1 part per million, and it has a short-term exposure limit (STEL) of 2 ppm for 15 minutes. Its threshold-limit value/time-weighted average (TLV/TWA) is 1 ppm for 8hour periods in a 40-hour work week, and it has an absolute ceiling limit of 2 ppm.

Symptoms of inhalation of formaldehyde at concentrations of 0.1 to 5 ppm include burning of the eyes, lacrimation (tearing), and irritation to the upper respiratory system. Coughing, pressure in the chest or head, and palpitation of the heart will occur upon exposure to levels of 5 to 20 ppm. Exposures to higher concentrations (50 to 100 ppm) can cause pulmonary edema, inflammation of the lungs, and death. The wheezing and coughing that begins shortly after exposure to even small amounts of formaldehyde are danger signs indicating that fresh air must be sought immediately.

Direct contact can cause severe irritation of the skin, and dermatitis is often reported. Typical reactions include sudden inflammation of the skin, usually after a few exposures.

When exposed to the gas itself, the most sensitive areas of skin may suddenly inflame. These include the eyelids, face, neck, scrotum, and flexor surfaces of the arms. There may also be outbreaks on the backs of the fingers, hands, wrists, and forearms.

Contact with the liquid can cause sensitization of the skin, and eye contact will result in severe corneal damage.

Ingestion of the material will produce very serious symptoms, including damage to the gastrointestinal tract, vomiting, dizziness, unconsciousness, and even death.


Whenever formaldehyde has been released, all possible exposure to the material must be avoided. Approach should be made from upwind, and proper breathing protection must be afforded all emergency personnel who must approach the release area. All populated areas downwind should be evacuated to avoid exposure to the gas, and all ignition sources must be eliminated to avoid the possibility of an explosion and fire.

Containers should be kept cool, preferably by water applied by unmanned appliances. If a container is being heated by impinging flame or intense, radiated heat, even approaching from the sides can be dangerous. Containers stressed by heat are always in danger of catastrophic failure. In particular, beware of getting between containers that may be affected by both radiant heat and flame.

Even though the formaldehyde gas may be dissolved in water, any applied heat will cause the gas to leave the water and begin to build up pressure within the tank. This build-up will be aided by the pressure exerted by water vapor also being evolved.

Since formaldehyde is so soluble in water, any gas leaking from a container or evolving from a spill of formalin may be “swept” from the air by applying a high-pressure spray or fog. Care must be exercised so that the water falling from this application is contained in as small an area as possible. In some situations, particularly when the temperature is low, large amounts of formaldehyde may not evolve from a spill. In that case, simply isolating the spill, and perhaps evacuating the immediate area downwind, may be all that’s necessary.

But entry of the spilled product into a sewer or waterway must be prevented. Entry into a waterway will threaten all downstream users of the water, and they must be properly warned. Even though the threat of explosion and fire may be lessened by formaldehyde’s dilution in a stream or river, users of the water may still be exposed to health-threatening amounts as the gas is released from the water in their plant or other occupancy.

The proper environmental authorities must always be notified and consulted when formaldehyde is accidentally released into a waterway. And aeration techniques such as sparging and airstripping must be considered. These techniques can best be carried out by trained salvage personnel, and they depend upon the ability to divert and hold contaminated water.

When the spill is large and evolution of a large amount of gas is possible, containment dikes should be built to restrict the movement of the liquid as much as possible. (Trenches may have to be dug to lead the solution from the spill area to a place convenient for containment.) Soil, sand, clay, peat moss, or any other absorbent material may be used. A containment pit may be dug if it’s not possible to control the situation with a pond. In fact, a pit is often better because it will have a smaller surface area exposed to the atmosphere, which means that under similar circumstances of temperature and wind movement, less evolution of gas will occur.

The pit may also lend itself better to covering the liquid to prevent escape of the vapors. This can be done by using a plastic sheet or tarp to cover the surface. Alcoholtype foam may also be used to slow the evolution of vapors.

Creating a pond or pit will also facilitate recovery and removal of the spilled product. The accumulation of the liquid in one place allows it to be pumped into secure containers and removed.

Once the spilled product is trapped in a containment pond or pit, gently adding water to the pool is an appropriate alternative in mitigating the incident. This procedure, called dilution, works by spreading the molecules of the product so far apart in the water that it takes much more heat to produce enough formaldehyde gas to reach the lower flammable limit. In effect, the flash point of the diluted solution will have been raised to a point unlikely to be reached. The only problem with this technique is that there must be enough room in the pond or pit to hold the increased volume.

Pumping equipment and tank wagons are almost always available from the manufacturer or shipper of the material, who, along with the consignee, or buyer, are the only parties who bear responsibility for removing the spilled product. If pumping techniques are used to remove contaminated product, the small amount of liquid remaining may be absorbed by using soil, sand, clay, fly ash, cement powder, or any other suitable sorbent. This material must also be properly disposed of, as it will have all of the hazards of the material absorbed. In some cases, the consignee may be able to salvage the material (even though the product may be so contaminated or diluted that it’s rendered useless to anyone).

Identification Numbers and Ratings


(United Nations/North America)

UN/NA 1198 (for flash point 141 ° F and below)

UN/NA 2209 (for liquid with flash point above 141° F)


(Chemical Abstract Service)



(Registry of Toxic Effects of Chemical Substances)



(Standard Transportation Commodity Code) Association of American Railroads,

Bureau of Explosives

4940341,4913144, 4940342, 4940365, 4913145, 4940364, 4913168,4913169


(Chemical Hazard Response Information System)

U.S. Coast Guard

FMS (for the solution)


(International Maritime Organization)

3.3, flammable liquid 9, miscellaneous dangerous substance

National Fire Protection Association 704 rating


U.S. Department of Transportation

Combustible liquid, ORM-A

Emergency personnel shouldn’t carry out salvage operations unless all of the following conditions exist: 1) the personnel are properly trained in salvage procedures, especially in the material involved; 2) they’re properly equipped with safe equipment that’s compatible with the product; 3) they’re properly educated in the hazards of the product; 4) life is being threatened; and 5) there’s no one else qualified to do it.

Personnel trained in clean-up techniques will also be needed to remove soil and other materials contaminated by the formaldehyde. The environmental authorities are the proper people to determine the extent of contamination, the material that must be removed, and the proper (and legal) disposal methods.

Fire situations

If the formaldehyde evolving from a spill of formalin is burning, extinguishment may be accomplished by the use of alcohol-type foam, carbon dioxide, dry chemicals, or water spray. With such a low ignition temperature, caution must be exercised due to the possibility of reignition. Once the fire is extinguished, water may be added to the pool to raise the flash point. Or water may be added during the fire; as dilution occurs, the fire will die down until the proper concentration is reached. Again, the volume of liquid will be made considerably larger by this technique.


Absolute ceiling limit—The

level of a material’s environmental presence to which a human being should never be exposed.

Air stripping—A process by which a material is pumped through an air chamber or sprayed into the open air at high pressure in order to remove contaminants.

Combustible liquid—A liquid with a flash point of 100° F or higher.

Flammable liquid—A liquid with a flash point that’s below 100° F.

Flexor—A muscle that serves to bend a part of the body.

If a container is leaking formaldehyde gas, the fire should not be extinguished unless the flow of gas can be stopped immediately after the extinguishment. If the flame is accidentally extinguished, water spray may be used to dissolve gas from the air and to disperse it to prevent an explosive reignition.

A deliberate burn may be considered if no life or property is threatened by it and if safe and easy extinguishment and salvage aren’t possible. But it’s much easier to allow a fire to continue burning than it is to deliberately ignite one. In addition to exposure threats, the possibility of an explosion upon ignition must be considered.

Protection and first aid

Protection must be provided against any exposure to skin and inhalation of vapors. This means total face, hand, foot, and body protection. Impervious materials, as claimed by manufacturers of protective clothing, include Butyl rubber, chlorinated polyethylene, natural rubber, neoprene, nitrile rubber, polyethylene, polyurethane, polyvinyl chloride, nitrile rubber/PVC, styrene-butadiene rubber, and nitrile-butadiene rubber.

Lacrimation—Production of tears.

ORM-A—A U.S. Department of Transportation designation standing for “Other Regulated Material.” The A stands for material that has an anesthetic, irritating, noxious, toxic, or other, similar property, and that can cause extreme annoyance or discomfort to passengers or crew if it leaks during transportation.

Pulmonary edema—Congestion in the lungs caused by the accumulation of blood and other fluids.

Sparging—A process by which air or other gas is bubbled through a liquid, solid, or gas to remove a contaminant.

Although gas masks with organic vapor cartridges are acceptable for concentrations below 50 ppm, it’s much safer to use positivepressure, self-contained breathing apparatus with a full facepiece whenever working in an atmosphere with formaldehyde present.

For inhalation victims, fresh air is a necessity. If breathing is difficult, artificial respiration should be given. For contact with the liquid, lots of water should be used to wash affected body areas. Eyes should be flushed for 15 minutes, with occasional lifting of the eyelids. Immediate medical attention is mandatory.

For ingestion, administer large amounts of water and induce vomiting. Again, get immediate medical attention for the victim.

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