Diacetyl, also called butanedioneorbutane-2,3-dione) is anorganic compoundwith the chemical formula (CH3CO)2. It is a volatile, yellow/green liquid with an intensely buttery flavour.
Diacetyl is primarily used an artificial food additive found in flours, chocolate, cooking oils, candy, chips, frosting and more. Most notably, it is responsible for the butter aroma and taste in microwave popcorn.
Sources & Routes of Exposure
Sources of Exposure [2,5]
Primary opportunities for exposure to diacetyl exist in occupational settings, where workers in flavouring companies’ facilities inhale vapours during food and beverage production processes. Part of the problem is that the FDA evaluates such flavouring chemicals as generally recognised as safe (GRAS) to be eaten, because they are food additives, but most of these substances have not been specifically tested for respiratory toxicity via inhalation.
Workers who make, use, or work near flavouring chemicals containing diacetyl may be at risk. Settings where these exposures may occur include:
- Flavouring plants
- Microwave popcorn plants
- Commercial and retail bakeries
- Snack food and candy plants
- Dairy products and packaged vegetable oil plants (e.g., margarine, cooking oil)
- Other flavoured food production plants
Routes of Exposure 
Diacetyl can be absorbed into the body by inhalation and by ingestion.
Health Effects [5,6,7,8]
Exposure to diacetyl causes the following acute health effects:
- Contact can irritate eyes. Eye contact with vapours can cause chemical burns, which require medical treatment to heal.
- Contact with the skin can cause irritation. It can result in a rash with dryness, redness, flaking, and cracking of the skin.
- Breathing diacetyl can irritate the nose and throat causing coughing and wheezing.
- High exposure to diacetyl may cause headache, drowsiness, lack of coordination and seizures.
Chronic Health Effects
Studies have shown an association with occupational exposure to certain flavourings such as diacetyl and the development of lung disease characterised by fixed airways obstruction. Some employees exposed to these flavourings have developed permanent lung damage including a rare disease called bronchiolitis obliterans. Symptoms include a dry cough, shortness of breath when using extra energy, and wheezing. The symptoms can start gradually, or severe symptoms can occur suddenly. The symptoms continue when you are not at work. Asthma medicines are not effective. Some workers do not have symptoms. Diacetyl also damages the respiratory system of test animals.
Diacetyl has not been tested for its ability to effect reproduction.
Diacetyl has not been tested for its ability to cause cancer.
Medical testing may include the following:
- Spirometry most often shows an obstructive pattern of ventilatory impairment that does not improve after bronchodilators and sometimes shows a restrictive pattern of ventilatory impairment. Careful comparison of spirometry test results over time is important to identify potentially concerning declines in lung function.
- Lung volume assessments are consistent with hyperinflation.
- Carbon monoxide diffusing capacity measurement is generally normal, especially early in the disease.
- Chest X-rays are usually normal but may show hyperinflation.
- High-resolution computerised tomography scans of the chest at full inspiration and expiration often reveal heterogeneous air trapping on the expiratory view and may demonstrate mosaic attenuation, bronchial wall thickening, cylindric bronchiectasis, and/or scattered ground glass opacities.
- Lung biopsies are not generally required for diagnosis, but may reveal evidence of constrictive bronchiolitis obliterans. Sometimes the term clinical bronchiolitis obliterans is used for patients who have medical test findings consistent with the disease constrictive bronchiolitis obliterans but do not have confirmatory biopsy results.
First Aid Measures
- Inhalation: If inhaled, remove to fresh air. If not breathing, give artificial respiration. If breathing is difficult, give oxygen.
- Skin Contact: In case of contact, immediately wash skin with soap and copious amounts of water.
- Eye Contact: In case of contact, immediately flush eyes with copious amounts of water for at least 15 minutes.
- Ingestion: If swallowed, wash out mouth with water provided person is conscious. Call a physician.
Fire & Explosion Information
- Diacetyl is a flammable liquid.
- It emits toxic fumes under fire conditions.
- Diacetyl vapour may travel considerable distance to source of ignition and flash back.
- Container explosion may occur under fire conditions.
- Diacetyl forms explosive mixtures in air.
Exposure Controls & Personal Protection
- Safety shower and eye bath.
- Use non-sparking tools.
- Mechanical exhaust required.
General Hygiene Measures
- Remove and wash contaminated clothing promptly.
- Wash thoroughly after handling.
Personal Protective Equipment
The following personal protective equipment is recommended when handling diacetyl:
- Respiratory Protection: Use respirators and components tested and approved under appropriate government standards such as NIOSH (US) or CEN (EU). Where risk assessment shows air-purifying respirators are appropriate use a full-face respirator with multi-purpose combination (US) or type ABEK (EN 14387) respirator cartridges as a backup to engineering controls. If the respirator is the sole means of protection, use a full-face supplied air respirator.
- Hand Protection: Compatible chemical-resistant gloves.
- Eye Protection: Chemical safety goggles.
|Exposure Limit||Limit Values||HE Codes||Health Factors & Target Organs|
|OSHA Permissible Exposure Limit (PEL) – General Industry||Not established|
|OSHA PEL – Construction Industry||Not established|
|OSHA PEL – Shipyard Employment||Not established|
|National Institute for Occupational Safety and Health (NIOSH) Recommended Exposure Limit (REL)||Not established|
American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Value (TLV) (2012)
Lung damage (bronchiolitis obliterans-like illness)
|CAL/OSHA PEL||Not established|
No regulation established