HSE information sheet 23(rev 1) states that Sources of fires in ductwork above open flame gas appliances include flambéing, flame-grilling and stirfrying. Ductwork should be regularly cleaned to prevent build up of grease and fat. This can be an unpleasant and awkward task and great care is needed to ensure a proper job is done as experience has shown this is often skimped.

Since 2004 the responsibility for risk assessment has been placed on building owners and/or occupiers.

Under the Food Hygiene (England) Regulations 2006, it is your responsibility:
To clean and maintain in a clean condition your ventilation canopy, filters and ducting. You are also obliged to assess the risk of fire due to the excessive build up of cooking oil deposits and grease residue under the Health and Safety at Work etc Act 1974 and the Fire Safety Regulations.

The Workplace Health, Safety & Welfare Regulations 1992 gives detailed on an employers responsibilities relating to workplace health and safety
The Health Technical Memorandum 03-01 is now a vital standard which provides essential best practice guidance for healthcare premises

Following guidance has been circulated by many local authorities to help you achieve this duty on behalf of Association of British Insurers:

  • Your canopy, filters and internal ducting should be checked for maintenance issues weekly and the entire ventilation system must be checked regularly by a competent person I.e. by a ventilation engineer annually.
  • The complete installation must be thoroughly cleaned on a frequency dependent on your cooking oil, fuel, cooking style and level of use.

Level of use No of hours per day Frequency
Heavy 12-16 3 monthly
Moderate 6-12 6 monthly
Light <2-6 12 monthly

These frequencies are guidelines and should be adjusted, taking into account the following additional potential risk factors:

  • The flash point of oil is reduced through repeated use, I.e. the older the oil the quicker it will ignite.
  • The use of solid fuel creates a greasy carbon film that is a highly combustible mixture.
  • Chicken fat and vegetable oil deposits are particularly easy to ignite.
  • Asian cooking styles produce very sticky syrup like grease that is very adhesive to metal surfaces and highly resistant to general purpose cleaners. Therefore a specialist degreasing chemical is necessary.
  • It is important that seasonal businesses thoroughly clean the entire ventilation system at the end of the season to prevent the hardening of the fat around fan motors etc.

A well designed ventilation system should have:

  • As short amount of ductwork as possible.
  • A minimum amount of directional changes.
  • A minimum/avoidance of horizontal sections.
  • The vertical ductwork installed within the building as far as possible.
  • The ductwork extending to a minimum of 1 metre above ridge height of the building.
  • The 'china mans hat' style cowl is an unsuitable terminal for this kind of ventilation system. It is more appropriate for the ductwork to terminate in a 'sleeve' or 'cone' style cowl.
  • Fire dampers should not be fitted on the extract side of any trunking system.
  • Fans must be Fire Rated.
  • Access hatches should be present on the ventilation system and situated not more than 3 metres apart.
  • A canopy should always be suitable for the cooking process and positioned so as to be most effective.
  • The canopy hood must be constructed of materials that can be kept clean and are non combustible I.e. stainless steel.


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