Diacetyl Exposure: What Food and Drink Manufacturers Need to Know

Exposure to Diacetyl vapour in the food and drink manufacturing sector

A recent HSE Safety Alert has highlighted serious workplace safety issues linked to exposure to diacetyl vapour in food and drink manufacturing. Diacetyl exposure has been associated with severe and irreversible lung disease, making it a critical concern for employers responsible for managing factory risks. In this bulletin, Morag McWilliam explains what steps you should take if your processes involve diacetyl or flavourings that may generate it.

Posted

18.01.2023

Written by

Morag McWilliam

What Is Diacetyl and Why Is It a Concern?

Diacetyl (CAS: 431‑03‑8), also known as 2,3‑butanedione, occurs naturally but is also produced synthetically for use in flavourings. It can be generated during coffee roasting and grinding, and may also appear during beer brewing. Synthetic diacetyl is widely used as a flavouring in food and beverage products and is classified as a hazardous substance under COSHH regulations.

Diacetyl is toxic if inhaled, can irritate the skin, damage the eyes, and is harmful if swallowed. Long‑term exposure can lead to bronchiolitis obliterans, an irreversible lung disease sometimes referred to as “popcorn lung.” This condition occurs when the bronchioles become scarred and narrowed, restricting airflow and reducing the body’s ability to absorb oxygen.

The disease was first identified in workers at microwave popcorn plants, where diacetyl vapour from flavourings caused significant respiratory harm. This discovery has since shaped modern legal safety requirements for controlling exposure to hazardous substances.

How Workers Can Be Exposed to Diacetyl

HSE research shows that heating diacetyl significantly increases airborne concentrations, raising the risk of exposure above Workplace Exposure Limits (WELs). This is particularly relevant in industries where diacetyl is heated or handled.

Coffee Manufacturing

During roasting and grinding, naturally occurring diacetyl levels can exceed WELs. Grinding beans while still warm (around 40°C) dramatically increases vapour release. Cooling beans to room temperature (16–20°C) before grinding reduces this risk and supports better managing factory risks.

Flavour Manufacturing

Airborne concentrations rise sharply when flavour mixtures containing diacetyl, even at low concentrations, are heated, added to hot processes, or spray‑dried. Exposure can occur during:

Opening containers
Decanting and weighing
Mixing
Spray drying
Packaging
Cleaning vessels or spillages

These activities represent significant workplace safety issues if not properly controlled.

Workplace Exposure Limits and COSHH Requirements

WELs for diacetyl are published in EH40/2005:

20 ppb (0.02 ppm) over an 8‑hour TWA
100 ppb (0.10 ppm) over a 15‑minute TWA

Safety data sheets for diacetyl or diacetyl‑containing mixtures should list these limits. Under the COSHH regulations, employers must assess, prevent, or adequately control exposure to hazardous substances so that levels remain below the WELs.

This forms part of your broader legal safety requirements as an employer.

What Should Employers Do Now?

1. Assess the Risk

If your processes involve diacetyl or flavourings likely to produce it, you must carry out a COSHH risk assessment. This helps identify hazards, determine who may be harmed, and evaluate the level of risk. A robust assessment is essential for managing factory risks effectively.

2. Check Safety Data Sheets

If diacetyl is not listed on a flavouring’s safety data sheet, contact the supplier to confirm whether it is present.

3. Substitute Where Possible

Use safer alternatives that do not contain diacetyl or similar compounds such as 2,3‑pentanedione.

4. Control Exposure

To achieve adequate control, measures must follow Schedule 2A of the COSHH Regulations, the Principles of Good Practice. These include:

Designing processes to minimise emissions
Considering all exposure routes (inhalation, skin, ingestion)
Using proportionate control measures
Selecting effective engineering controls
Providing PPE where necessary
Regularly reviewing control measures
Training employees on hazards and controls
Ensuring new controls do not introduce additional risks

It’s important to note that WELs do not represent “safe” levels. Adequate control means demonstrating compliance with all eight principles, not simply staying below the limit.

Where substitution is not possible, such as natural diacetyl produced during coffee roasting, strict controls must be implemented:

Keep flavourings below 4°C to reduce vapour release
Enclose processes and use extraction to control emissions
Cool coffee beans below 20°C before grinding
Add diacetyl flavourings at the final stage using enclosed or automated systems
Provide suitable PPE and RPE if exposure cannot be reduced below WELs

These steps form part of essential health and safety support for your workforce.

Health Surveillance

If workers may be harmed by diacetyl exposure, you must introduce a health surveillance programme. Your COSHH assessment will determine whether this is required. Surveillance should be developed with an occupational health provider to ensure compliance with legal safety requirements.

Carbon Monoxide (CO) Considerations

Carbon monoxide is also produced during coffee processing. Measures used to control diacetyl, such as enclosure and extraction, will also help reduce CO emissions. As part of your risk assessment, sampling should be carried out to determine whether additional controls are needed.

Final Thoughts

Diacetyl exposure represents a significant challenge for employers facing modern workplace safety issues. By following COSHH regulations, implementing effective controls, and seeking appropriate health and safety support, organisations can protect workers and ensure compliance with UK legal safety requirements.