Diacetyl (also called butanedione or butane-2,3-dione) is an organic compound with the chemical formula (CH₃CO)₂. It is a yellow/green, volatile liquid with a strong buttery aroma and taste.
Diacetyl naturally forms during beer and wine fermentation as yeast breaks down glucose into ethanol. It’s also found in small amounts in coffee, vinegar, honey, dairy, and fruits.
At low levels, it adds a slippery texture to drinks, while at higher levels, it gives off a butterscotch-like flavour. It has been used as a marker for flavouring vapour exposure, especially in industries like microwave popcorn manufacturing.
Other similar chemicals used as possible substitutes include acetoin, 2,3-pentanedione, 2,3-hexanedione, and 2,3-heptanedione.
What is Diacetyl used for?
Diacetyl is mainly used as a food flavouring. It is commonly added to:
Flour
Chocolate
Cooking oils
Candy
Chips
Frosting
And most famously, microwave popcorn for its buttery aroma and taste.
Diacetyl is used as a food flavouring and commonly added to candy.
Sources and Routes of Exposure
Source of Exposure
Most exposure to diacetyl happens at work in food and flavouring facilities. While it is safe to eat in small amounts, it is not well-tested for safety when inhaled.
Industries where workers may breathe in diacetyl vapours include:
Flavouring production facilities
Microwave popcorn factories
Commercial and retail bakeries
Snack food and candy factories
Dairy and vegetable oil plants (e.g., margarine and cooking oil)
Other flavoured food processing plants
Routes of Exposure
Diacetyl enters the body mainly by:
Inhalation
Ingestion
Health Effects
Acute Effects
Short-term exposure to diacetyl can cause:
Eye irritation or chemical burns from vapours
Skin irritation, rash, redness, dryness, and cracking
Throat and nose irritation, coughing, and wheezing
At high levels: headache, drowsiness, poor coordination, and seizures
Chronic Effects
Long-term or repeated exposure can lead to serious lung damage, especially in workers. This includes a rare condition called bronchiolitis obliterans (also known as “popcorn lung”), which causes:
Dry cough
Shortness of breath (especially with exertion)
Wheezing
Permanent lung damage
Asthma medications do not help, and some affected workers may not show symptoms at all. Diacetyl has also caused lung damage in test animals.
Reproductive Hazard
Diacetyl has not been tested for its effect on reproduction.
Cancer Risk
Diacetyl has not been tested for its ability to cause cancer.
Medical Testing
Testing for diacetyl exposure may include:
Spirometry: Shows impaired airflow that does not improve with bronchodilators
Lung volumes: May show hyperinflation
CO diffusing capacity: Often normal in early disease
Chest X-rays: Usually normal but can show hyperinflation
CT scans: May show air trapping, mosaic patterns, bronchial wall thickening, or ground-glass opacities
Lung biopsies: Not usually required, but may confirm bronchiolitis obliterans
Safety
First Aid Measures
Inhalation: Move to fresh air. Give artificial respiration or oxygen if needed.
Skin Contact: Wash immediately with soap and water.
Eye Contact: Rinse eyes for at least 15 minutes with water.
Ingestion: Rinse mouth with water. Do not induce vomiting. Call a doctor.
Fire & Explosion Information
Flammable liquid
Releases toxic fumes during fires
Vapours may travel and ignite at a distant source
Containers can explode when heated
Forms explosive air mixtures
Exposure Control & Personal Protection
Engineering Controls
Use a safety shower and eyewash station
Use non-sparking tools
Provide mechanical exhaust ventilation
General Hygiene Measures
Remove and wash contaminated clothing immediately
Wash hands and exposed skin thoroughly after handling
Personal Protective Equipment (PPE)
Respiratory Protection: Use approved respirators (e.g., NIOSH or EN 14387 type ABEK)
Use full-face respirators if needed
Hand Protection: Wear chemical-resistant gloves
Eye Protection: Use chemical safety goggles
Regulation
United States
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)
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