Exposure to Diacetyl vapour in the food and drink manufacturing sector

Exposure to Diacetyl vapour in the food and drink manufacturing sector

An HSE Safety Alert was released last week about exposure to diacetyl vapour in food and drink manufacturing. It has been found that exposure to the vapour can lead to severe and irreversible lung disease. In this bulletin, Morag McWilliam lets you know what you should do if your processes include the use of diacetyl.

What is Diacetyl and why is exposure to it a concern?

Diacetyl (CAS: 431-03-8), also known as 2,3-butanedione, is a naturally occurring organic compound but is also manufactured synthetically.

Diacetyl vapour can be generated as a by-product during the roasting and grinding of coffee beans and may also be present during the brewing of some beers.

Synthetic diacetyl is used as a flavouring for some food and beverage products and is classified as a hazardous substance.

Diacetyl is toxic if inhaled, can cause skin irritation and eye damage by contact and is harmful if swallowed.

Exposure to diacetyl can also cause bronchiolitis obliterans which is an irreversible lung disease.

The very small airways of the lungs are called bronchioles. Bronchioles can become injured as a result of inhaling a harmful substance or due to an infection. Most of the time, the injury heals normally. Occasionally the cellular repair process goes into overdrive, causing the build-up of scar tissue. The thick scar tissue blocks the bronchioles and prevents air from passing through to the alveoli, or air sacs. This impairs the body’s ability to absorb oxygen. The scarring and narrowing of the bronchioles may continue to worsen over time, eventually resulting in respiratory failure.

The accelerated cellular repair process can be triggered due to exposure to hazardous substances like diacetyl.

The discovery of bronchiolitis obliterans as an occupational disease was first made in workers at a microwave popcorn plant who had inhaled the flavouring chemical diacetyl. Thus, bronchiolitis obliterans became known as ‘popcorn lung’.

How can I be exposed to diacetyl?

Scientific studies undertaken by the UK Health and Safety Executive show that heating diacetyl above certain temperatures significantly increases airborne concentrations and the potential for exposures above Workplace Exposure limits (WELs).

This is of particular significance in the following industries which involve the heating and or handling of diacetyl:

Coffee manufacturing

Exposure levels during bean roasting and grinding can exceed WELs. The amount of diacetyl generated naturally during bean grinding is temperature dependent.  Concentrations are significantly greater if the roasted beans are ground when still warm (around 400C) and reduced if the beans are cooled between roasting and grinding down to room temp (around 16-20C).

Flavour manufacturing

Airborne concentrations and the potential for exposures above safe workplace limits are significantly increased if flavour mixtures containing diacetyl, even at low concentrations (below 5%) are heated, added to hot processes or spray-dried.

Risk of exposure can occur during

  • opening of diacetyl or flavouring containers
  • decanting and weighing
  • mixing
  • spray drying to produce powdered mixtures
  • packaging
  • cleaning of vessels or spillages

Hazardous substance Workplace Exposure Limits (WELs)

WELs for diacetyl was published in EH40/2005 Workplace Exposure Limits.

Limits are at 20 parts per billion (ppb) or 0.02 parts per million (ppm) over an 8-hr time-weighted average (TWA) and 100 ppb or 0.10 ppm over a 15-min TWA period.

Suppliers’ safety data sheets for diacetyl or for mixtures containing diacetyl should list these WELs.

The Control of Substances Hazardous to Health (COSHH) Regulations 2002 (as amended) require employers to ensure work-related exposure to hazardous substances is assessed, prevented or adequately controlled so that it is below the WELs.

What should I do now?

Assess the risk

If your processes include the use of diacetyl and food flavourings that contain diacetyl or are likely to produce diacetyl, then you must carry out a risk assessment. Your risk assessment will help you to identify the hazards associated with the potential for exposure, understand who might be harmed and how to evaluate the risks and decide on control measures.

Check the safety data sheet

If diacetyl is not mentioned on a safety data sheet for food flavourings (which are likely to contain it) you should contact the supplier to confirm if it is present or not


Substitute a safer alternative product.  Substitutes should not contain compounds similar to diacetyl such as 2,3-pentanedione.

Control risk of exposure

To be considered ‘adequate’, control measures implemented should be in accordance with Schedule 2A of the COSHH Regulations the ‘Principles of Good Practice for the Control of Exposure to Substances Hazardous to Health.’ The principles are as follows:

  • Design and operate processes and activities to minimise the emission, release and spread of substances hazardous to health.
  • Take into account all relevant routes of exposure – inhalation, skin and ingestion – when developing control measures.
  • Control exposure by measures that are proportionate to the health risk.
  • Choose the most effective and reliable control options that minimise the escape and spread of substances hazardous to health.
  • Where adequate control of exposure cannot be achieved by other means, provide, in combination with other control measures, suitable personal protective equipment.
  • Check and review regularly all elements of control measures for their continuing effectiveness.
  • Inform and train all employees on the hazards and risks of substances with which they work, and the use of control measures developed to minimise the risks.
  • Ensure that the introduction of measures to control exposure does not increase the overall risk to health and safety.

It is important to note that WELs should not be classed as ‘safe’ levels of exposure which indicate that adequate control is being achieved.

For exposure to be considered adequate by the Health and Safety Executive, the employer must be able to show that they have implemented control measures in accordance with the 8 principles described above.

In the case of diacetyl, if substitution is not a viable option (for example if diacetyl is a natural by-product such as during coffee roasting), then strict controls must be implemented. These may include the following measures:

  • Keep the flavouring at a low temperature (below 4°C) as this will significantly reduce vaporisation.
  • Enclose the process and use extraction, to control diacetyl vapour emissions at source.
  • For coffee manufacture, cool the coffee beans (to at least below 20ºC) pre-grind.
  • For diacetyl flavouring manufacture and use, add the flavouring at the last stage of production and via an enclosed or automated system.
  • Where the above controls do not reduce exposure below the WEL, you should consider providing suitable personal protective equipment (PPE), including suitable respiratory protection equipment (RPE).

Health surveillance

If there is a reasonable likelihood that workers may be harmed by diacetyl you must introduce a health surveillance programme. Your risk assessment will help you decide if this is required. A health surveillance programme should be devised in consultation with an occupational health provider.

Carbon Monoxide (CO)

Carbon monoxide is also known to be a by-product of coffee processing. Control of diacetyl through enclosure and extraction will also help control CO emissions. HSE recommends that as part of a risk assessment process, you carry out sampling to establish whether any further controls for CO might be necessary.

If you would like to have a chat about the risks of diacetyl exposure in your business, then please don’t hesitate to get in touch with [email protected].

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