Formic acid is a combustible, corrosive, toxic, irritating, colorless liquid with a pungent odor. In its natural state, it is the major ingredient in the stinging chemical of ants and other insects. Its main uses are in dyeing textiles and as an organic chemical intermediate used in the production of other chemicals such as fumigants, insecticides, perfume solvents, refrigerants, and vinyl resin plasticizers. It is also used as an antiseptic, a laboratory reagent, an ore flotation agent, and a natural latex coagulant.


Formic acid has a flash point of 122°F, an ignition temperature (sometimes referred to as the autoignition temperature) of 813°F, and an explosive range of from 18 percent to 57 percent in air. It has a specific gravity of 1.21, a molecular weight of 46, and a vapor density of 1.59. It freezes at 46°F, boils at 213°F, and is totally miscible with water. Its molecular formula is HCOOH.


Formic acid`s major hazard is corrosivity. In concentrated solutions (the forms in which it is usually shipped are 85-percent to 98-percent solutions), it is extremely corrosive to human tissue and metals. In concentrations above 98 percent, formic acid is unstable and will decompose, releasing toxic carbon monoxide gas.

A combustible liquid, formic acid has a flash point of 122°F, meaning that any time the liquid`s temperature reaches this level, it is capable of generating vapors sufficient to form an ignitable mixture with the air near the surface of the liquid or its container. Its ignition temperature of 813°F is easily reached by all common ignition sources.

The “saving grace” of the properties of formic acid is that its lower explosive (flammable) limit is extremely high (18 percent)–a tremendous amount of the vapors must be present in air before an explosive mixture is formed with that air. At most concentrations below 18 percent in air, an extremely strong pungent odor of the acid will be present. In many situations, the level will be high enough to be deadly to unprotected lungs.

The terms lower flammable limit and lower explosive limit are virtually synonymous since, when the vapors of a flammable or combustible liquid (or flammable gas) are ignited, an explosion is the first phenomenon to occur. A fire will follow if all the fuel has not been consumed in the explosion. Actually, the terms flammable range, lower flammable limit, and upper flammable limit are really misnomers and are misleading. The terms should be explosive range, lower explosive limit, and upper explosive limit.

Formic acid`s hazardous properties of combustibility and high lower explosive limit can lull emergency responders into a false sense of security when handling accidental releases of the product. First, most emergency responders do not expect corrosive materials like acids to burn. The fact is that all organic acids, of which formic acid is the simplest, will burn. (All organic materials will burn.) Formic acid is very dangerous in a fire, since radiant heat from the fire (flames) will cause temperatures to easily reach or exceed its flash point.

Once the flash point has been reached, the danger from an explosion of the formic acid vapors becomes very real. Remember, although the lower explosive limit of formic acid is very high, the flash point of a liquid is that temperature at which enough vapors are present to form the explosive mixture with the air. That means that at 122°F or higher, enough vapors of formic acid are being generated to reach that 18 percent lower limit. At temperatures below the lower flammable (explosive) limit, there must be a tremendous amount of formic acid vapors in air, which will be very corrosive, toxic, and irritating.

Formic acid is a toxic material with a TLV-TWA (threshold limit value-time weighted average of five ppm (parts per million parts of air). Inhaling the vapors of formic acid may cause respiratory tract irritation, burns, breathing difficulty, chest pains, coughing, fatigue, nausea, vomiting, and pulmonary edema. Unprotected personnel caught in particularly high concentrations of vapor could suffer fatal consequences.

Contact with the eyes may cause blurred vision, reddening, conjunctivitis and destruction of the cornea, and other permanent damage.

Ingesting formic acid may burn the mouth, tongue, esophagus, and stomach. It can also cause abdominal spasms, coughing, constriction of the throat, breathing difficulties, kidney damage, diarrhea, dizziness, vomiting, shock, and unconsciousness. Death can occur, depending on the concentration of the acid, the amount ingested, and the effectiveness of first-aid and emergency medical treatment.

Contact with the skin may cause blistering, burns, inflammation, itching, reddening, and tissue damage. Skin burns can be very deep and especially slow healing. Permanent tissue damage can occur. Damage to the skin depends on the acid concentration, the amount contacted, the length of contact, and how long before first aid was administered.

Formic acid is a stable chemical during storage and transport as long as it is a solution with a concentration weaker than 98 percent. However, like all other flammable or combustible liquids (or anything else that will burn), it should always be stored or shipped separately from oxidizing agents (materials that support combustion, usually by providing oxygen to the fuel). With these two legs of the fire triangle present, all that is needed for a fire or explosion is a suitable ignition source. In the case of formic acid, it is anything that will provide enough energy to raise the available fuel to 813°F.

Formic acid is incompatible with chromic acid, hydrogen peroxide, nitric acid, all permanganates, and other strong oxidizing agents. Contact with these compounds could cause violent reactions. Prevent all oxidizers and strong mineral acids (such as sulfuric acid and hydrochloric acid, among many others) from contacting formic acid. Formic acid is also incompatible with strong bases, including but not limited to sodium, potassium, and ammonium hydroxides.


In an emergency involving any appreciable quantity of accidentally released formic acid, activate the community`s emergency response plan. The incident commander must consult with all available chemical and environmental experts the community can muster. In today`s society, the local government and fire department may be held liable for any environmental or property damage incurred due to incorrect procedures. If the formic acid container has been breached and liquid and vapors are escaping, attempt to stop the leak if it can be done without risk to the responders and if the proper equipment is available. Always allow vapors and fumes of hazardous materials to dissipate completely before reentering the incident area without proper special protective gear. Entry without special protective gear should be made only if lives are to be saved and the rescuers will not be in immediate danger. Water fog or spray applied to formic acid vapors downwind of the spill may absorb some vapors and accelerate their dispersal into the atmosphere. Be sure to contain any water runoff; it may contain varying amounts of formic acid.

Consider evacuating local and downwind residents early in the operation to prevent their exposure to formic acid and to allow vapors or fumes to dissipate. Formic acid spills may expose downwind areas to toxic concentrations over considerable distances because of its vapor density of 1.59. These vapors will “hang together” and flow along and accumulate in low spots of the terrain and confined spaces. Unless wearing proper respiratory protection, anyone exposed to these vapors can be injured in a very short time. If these vapors build up to the lower explosive limit and then contact a suitable ignition source, the vapors will ignite and flash back to the source of the vapors.

Therefore, eliminate all possible ignition sources near and downwind of the release source. Do not expose the container to a heat source. The heat`s breakdown of formic acid will generate large amounts of toxic and flammable carbon monoxide. Keep the formic acid away from strong oxidizers and other incompatible materials. Use containment dikes and pits to prevent the spread of the product. Environmental authorities mobilized with other emergency responders will have to monitor the spread of contamination. The possibility of ignition of the vapors is low if the ambient temperature is low and the temperature of the product is correspondingly low. Vapors of formic acid will be generated no matter what the temperature; but these vapors, which will be in the highest concentration near the release, can easily be handled by sweeping the air near the spill with water fog or a high-pressure spray.

If formic acid enters a pond or lake, it might be fatal to any aquatic life near the point of entry. The product will mix rapidly with the water and slowly spread away from the point of entry. If the entry is into a river or stream, the contamination will be carried away and mixed throughout the water at a rate proportional to the speed of the moving water. If the volume of moving water is great, the material will dissolve faster and be diluted at a faster rate. Immediately notify all possible downstream users of the water. Contaminated water entering into industrial operations could cause explosions as the heat of the process in which the water is being used drives the formic acid from the water solution. Environmental authorities on the scene will have to determine the extent of contamination and when the water will be safe to use once again.

Prevent formic acid from entering sewers and waterways. If it enters a sewer, it can evolve vapors that could ignite and cause an explosion at any manhole or catch basin along the system. This explosion could spread throughout an entire city.

Formic acid may be neutralized by adding calcium carbonate, sodium bicarbonate, or calcium hydroxide. The latter is also known as “slaked lime” and is caustic enough to be hazardous by itself. As in any use of neutralizing agents, a small quantity of the material to be neutralized should be removed from the main release and small amounts of the neutralizing agent should be added to determine reactions. In some instances, a reaction may be strong enough to warrant adding the material in another manner, such as in its pure form, as a concentrated water solution, or as a weak water solution. Use litmus paper to determine if the neutralization attempt has worked.

Formic acid not contained in the containment pond or pit may be salvaged by pumping or suctioning the liquid into secure containers. Properly trained and equipped (sparkproof, compatible tools and equipment must be used) professionals should conduct salvage–never firefighters or other emergency responders unless they have been properly trained and equipped to the same level as the professionals. Any remaining formic acid in the containment dike or pit may be absorbed with sand or other noncombustible absorbent material or sorbent known to be compatible. Dispose of the contaminated sorbent in accordance with federal, state, and local regulations. Remove any soil contaminated during the incident and handle it in the same manner.


Treat containers of formic acid exposed to the radiant heat from an approaching fire or impinging flame as any other combustible liquid. Be aware, however, of added danger from the by-products of decomposing formic acid, which not only are toxic but also flammable. The containers will rupture violently when the pressure of the vapors from the heated liquid rises faster than the safety relief devices can vent to the atmosphere. The evolved carbon monoxide will explode as it is released. Any carbon monoxide not consumed in the explosion or fire will pose a deadly threat to unprotected personnel.

Formic acid is very reactive at high temperatures and pressures. Containers may rupture violently in fire. Contact with other chemicals such as strong oxidizers, mineral (inorganic) acids, and bases could cause very violent reactions.

Cool containers of formic acid threatened by heat and fire with flooding amounts of water delivered by unmanned appliances positioned as far away as possible. The potential for the container`s failing catastrophically and generating carbon monoxide makes this product extremely dangerous in a fire.

Fires involving formic acid may be fought with extinguishing agents such as alcohol foam, carbon dioxide, dry chemical, and water spray. Do not extinguish burning vapors escaping from the container unless the flow of those vapors can be stopped safely and immediately after extinguishment. The effectiveness of fighting fires with these extinguishing agents depends on the amount of agent available during the fire, the amount of fuel burning, weather conditions, the terrain, manpower and equipment available, and the ability to deliver the extinguishing agent effectively.


Choose protective clothing and equipment that will prevent any chance of skin or eye contact with formic acid. Equipment should include rubber boots, gloves, face shields, splashproof safety goggles, and other impervious and chemical-resistant clothing. Total encapsulating suits with SCBA will be needed to prevent contact with the vapors. SCBA with full face piece (or the equivalent) must be worn whenever participating in an incident where formic acid has been released.

Total encapsulating suits made of butyl rubber, neoprene, polyvinyl chloride (PVC), and SaranexTM may offer protection. As always, ask the manufacturers of the suits and the formic acid for their recommendations. Just remember that protection is a relative term. A material may be used because it resists a particular chemical in the laboratory, but the same material used in a total encapsulating suit may fail because it is thinner than that used in the lab tests. Other factors affecting the protection level include the integrity of the seams and the coverings on the zippers, the concentration of the chemical in question, and the duration of the exposure.


Inhalation. Move the victim to fresh air and keep him warm and relaxed. If the victim is unconscious, administer artificial respiration. (Warning: Administering mouth-to-mouth resuscitation may expose the first-aid provider to formic acid in the victim`s lungs or vomit.) Administer oxygen if the victim remains unconscious or breathing is difficult. Get medical attention immediately.

Ingestion. If the victim is conscious, administer water, milk, or milk of magnesia. Do not induce vomiting. Never attempt to make an unconscious person vomit.

Eye contact. For liquid or vapors, immediately flush the eyes with water for at least 20 minutes; occasionally lift the eyelids. Get medical attention immediately.

Skin contact. Remove all contaminated clothing as soon as possible. Wash the affected body areas with large amounts of soap and water. Get medical attention immediately. Place all contaminated clothing in a closed container for storage until it can be laundered or discarded. If clothing is to be laundered, inform the person performing the operation of the contaminant`s hazardous properties. Discard all contaminated leather goods.


aminic acid

formylic acid

hydrogen carboxylic acid

methanoic acid



(Chemical Abstract Services)



(Standard Transportation Commodity Code)

4931320 pure form, 4931431 water solutions


(Registry of Toxic Effects of Chemical Substances)



(United Nations/North America)



(Resource Conservation and Recovery Act)



(Chemical Hazard Response Information System)



(U.S. Department of Transportation)


NFPA 704 Rating

(National Fire Protection Association)



(International Maritime Organization)

8.0, corrosive

FRANK L. FIRE is the vice president of marketing for Americhem Inc. in Cuyahoga Falls, Ohio. He`s an instructor of hazardous-materials chemistry at the University of Akron as well as an adjunct instructor of haz mats at the National Fire Academy. Fire is the author of The Common Sense Approach to Hazardous Materials and an accompanying study guide, Combustibility of Plastics, and Chemical Data Notebook: A User`s Manual, published by Fire Engineering Books. He is an editorial advisory board member of Fire Engineering.

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