Last reviewed 30 October 2013

Caroline Raine looks at the dangers of using hydrazine and how workers can stay safe when handling it.


Hydrazine is a toxic, flammable and corrosive chemical that has a number of uses; it is widely used as a laboratory chemical, a precursor to polymerisation catalysts and pharmaceuticals and as a foaming agent in the manufacture of polymer foams. It is used as a blowing agent in the manufacturing process of plastics that are then used in vinyl flooring and auto foam cushions. Other uses include nickel plating, photography development and in the production of agricultural chemicals (eg maleic hydrazide).

Hydrazine is found in tobacco and cigarette smoke, and has, despite being a carcinogen, been used in medication for the treatment of sickle cell anaemia and cancer.

Hydrazine is also often used to reduce corrosion of metal and build-up of scale in power stations, steam and boilers. Hydrazine, a colourless liquid, is highly soluble in water. As a powerful reducing agent, it will reduce oxygen content, forming nitrogen and water, with no resulting dissolved solids. At high temperatures and pressures, the reaction between hydrazine and dissolved oxygen also forms very small quantities of ammonia. This ammonia carries over into the steam and helps to reduce the acidity of the resulting condensate, thus reducing the likelihood of corrosion. Hydrazine is known as an “oxygen scavenger”.

Hydrazine is corrosive, toxic and flammable in the presence of open flames, sparks, heat, and oxidising materials. It is also highly explosive in the presence of oxidising materials and metals and incompatible with moisture and acids.

The molecular formula for hydrazine is N2H4 and it has a flash point of 52°C.


According to EU Directives 67/548/EEC or 1999/45/EC (CHIP), hydrazine is classified as Toxic, Corrosive, and Dangerous to the Environment. Risk phrases indicate that hydrazine is flammable and may cause cancer.

According to Regulation (EC) No. 1272/2008 (CLP), hydrazine is flammable, toxic (oral, dermal, inhalation and to the aquatic environment), corrosive and a carcinogen.

Hydrazine is also included in the Candidate List of Substances of Very High Concern (SVHC), according to Regulation (EC) No. 1907/2006 (REACH).

For transport, hydrazine is classified as corrosive with subsidiary hazards, flammable liquids and toxic substances.

Occupational exposure

Within the UK, those using and working with hydrazine must comply with the Control of Substances Hazardous to Health Regulations 2002 (COSHH) (as amended). The Health and Safety Executive (HSE) sets workplace exposure limits for substances and they can be found in EH40/2005 Workplace exposure limits.

Hydrazine has a short-term exposure limit (STEL 15-minute reference period) of 0.1ppm/0.13mg/m3 and a long-term exposure limit (8-hr TWA reference period) of 0.02ppm/0.03mg/m3.

There are a number of gas monitors available to ensure that the exposure limits are never exceeded. These range from personal monitors that individuals wear to room-based monitoring. Many work on a colour change concept so that it is visible when there has been exposure to hydrazine; others give digital readings showing the ppm in the air. Hydrazine has been identified as a possible human cancer and so levels of exposure should be as low as possible.

Health effects and health surveillance

According to MSDS 2005, hydrazine is toxic to blood, kidneys, lungs, the nervous system and mucous membranes. Liquid and spray contact can produce tissue damage to mucous membranes, particularly the eyes, nose, mouth, and respiratory tract. Skin contact may produce burns and inhalation of spray may produce irritation of the respiratory tract, with repeated or prolonged exposures producing target organ damage. Severe over-exposure can result in death.

Acute respiratory exposure can result in dyspnoea and pulmonary oedema, pneumonia, tracheitis, and bronchitis and lung damage.

Potential symptoms of hydrazine exposure include: eye, nose and throat irritation, temporary blindness, dizziness, nausea, dermatitis, skin and eye burns, malar (cheek) rash and photosensitivity.

The International Programme on Chemical Safety (IPCS) recommends that those handling hydrazine, or hydrazine solutions, should undergo medical examination once a year. The emphasis should be on the functioning of the central nervous system, liver and kidneys, and on disorders of the skin, eyes and blood.

The IPCS states that hydrazine is a possible carcinogen and a strong skin sensitiser, and that cross-sensitisation to hydrazine derivatives may occur.

Personal Protective Equipment

Hydrazine can be absorbed through the skin and dermal absorption may lead to systemic toxicity. It is therefore imperative that there is no skin contact. Personal Protective Equipment (PPE) is required when using or handling hydrazine. Hydrazine is extremely toxic and corrosive. At low levels of exposure, it causes coughing and lung and throat irritation; at higher levels, tremors and nausea; with prolonged exposure, liver and kidney damage. When handling and using hydrazine, the following PPE should be worn:

  • eye protection

  • gloves

  • full suit

  • respirator

  • boots.

Eye/face protection should meet appropriate standards such as NIOSH (US) or EN166 (EU). Gloves should satisfy the specifications of EU Directive 89/686/EEC and the standard EN 374 derived from it. Butyl-rubber should be worn for full contact or nitrile gloves for splash contact. Complete suit protecting against chemicals must be flame retardant antistatic. Respirators should also meet government standards


Hydrazine should be stored in a cool safe place. Containers should be tightly closed in a dry and well-ventilated place. Containers that are opened must be carefully resealed and kept upright to prevent leakage. It is recommended that the area be secured, so a lockable chemical cupboard is sensible in order to restrict access.

All sources of ignition should be eliminated, eg no smoking or the use of mobile phones. Take measures to prevent the build-up of electrostatic charge, use non-sparking tools and intrinsically safe equipment.

Keep away from oxidising agents, oxygen, copper, zinc and organic materials.


In the event of a spillage, it is important to ensure protection to people, the environment and property (in that order).

Evacuate all personnel to safe areas. Ensure that the correct PPE is worn before attempting to deal with a spill. Be sure to remove all sources of ignition and ensure there is adequate ventilation. Vapours can accumulate to form explosive concentrations. Due to the density of hydrazine, vapours can accumulate in low areas.

Ensure that the product cannot enter into any natural watercourses, ie streams, rivers, etc. Entry into watercourses can be prevented by sealing drains and absorbing the spillage with soil, sand or any absorbent material.

Once the spillage has been contained, it can be collected with an electrically protected vacuum cleaner or by wet-brushing. It should then be placed in a clearly marked container for disposal as hazardous waste according to local regulations. Specialist contractors would be able to help with this if required.

Specialist contractors would also be able to deal with the spill so never attempt to clear up a spill if there is any uncertainty as to what should be done. Seek advice and assistance.

First aid

In the event that a person or persons is exposed to hydrazine, good initial first aid can help minimise the consequences. In all situations, medical advice should be sought, and if possible, a copy of the Safety Data Sheet should be taken.

For eye and skin contact, wash thoroughly with plenty of water for at least 15 minutes and seek medical advice. If there has been skin contact then all contaminated clothing, shoes and jewellery should be removed immediately. In the event of inhaling hydrazine fumes, move the person into fresh air and seek medical advice. Should ingestion occur, never induce vomiting and never give anything by mouth to an unconscious person. Rinse mouth with water and give a little water to drink, and again, seek medical advice.