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Understanding Kitchen Ventilation
In the kitchen, a ventilation system removes heat and grease coming from cooking
equipment, steam from ware washing and boiling and dangerous carbon monoxide fumes
produced from the combustion of gas cooking equipment.
Front of house, a ventilation system removes smoke, keeps the restaurant or bar at a
pleasant temperature and reduces humidity. Externally, it can remove cooking smells, which
are being discharged into the atmosphere to the annoyance of other businesses or houses in
A kitchen ventilation system, incorporating extract and supply air is not an optional extra any
more, but a legal requirement. Legislation regarding health and safety in the workplace
insist on kitchens being well-ventilated and comfortable to work in. This is not met by just
opening a window or door, which in itself would give access to airborne pollution. Tobacco
smoke in public areas is a huge issue both for customers and staff. Any cooking smells being
discharged into the outside is not just a nuisance to neighbours, but also a reason to be
refused planning permission for any kitchen redevelopment or the subject of an enforcement
notice for an existing kitchen.
It is now a requirement to comply with BS-6173 to have the gas supply interlocked with both
the extract and supply air systems. This automatically switches off the gas supply should the
extraction system stop working for any reason and a fire occur in the extraction canopy.
There are two main types of kitchen ventilation, canopy or ventilated ceiling. Canopies are
the most popular in commercial kitchens. Both systems involved a system of filters and fans,
exhausting the heat, dangerous gases and humidity and trapping particles of food and fat
debris while at the same time introducing cleaned and cooler air into the kitchen.
The system to fit depends on the nature of the kitchen operation, the available space and
nature of the cooking. One of the variable features of a kitchen ventilation system is the type
of filtering system used to remove food debris, notably grease. Grease is not just an
unwanted smell; it is also a high fire risk within the extraction systems. There are six types
of grease filter available.
Mesh filters – These are layers of metal mesh onto which the grease particles are deposited
as they are drawn through the system. They require regular washing, are not efficient at
removing high levels of grease and in a high-fat kitchen can pose a fire risk in the extraction
system. These types of filters should only be used where there will be little or no grease held
in suspension within the exhaust gases, therefore, these filters should not be installed above
deep fat fryers, chargrills, griddles, salamander grills or bratt pans to be used for shallow
frying. Cleaning of these filters is done by soaking them in very hot water with a de-greasing
detergent, although this will eventually destroy the internal mesh and require the filter to be
Baffle filters – More efficient than mesh filters, as they work by making the air change
direction and velocity, which separates the grease from the air stream with the deposited
grease running off into grease collection troughs. These types of filters are suitable for
general cooking with moderate grease load applications. These filters should only be
manufactured from stainless steel. Cleaning procedure is very simple as they can be simply
washed in a commercial dish washing machine.
Cartridge filters – These types of filters should not be confused with disposable filters, as
disposable filters should never be used in commercial kitchen extract systems. Cartridge
filters are stainless steel filters, which are more efficient than baffle filters as they are
intended for moderate to heavy grease load applications. These types of filters will be
cleaned, like the baffle filters, by running through a commercial dishwashing machine.
Water wash – A more advanced cartridge system where the filters are subject to an
automatic internal washing cycle to clean them, usually at the end of the working day. They
need a hot water supply and are among the more expensive systems, but are very good at
Continuous water mist - Regarded as one of the most effective of grease extraction systems,
but requires plumbing and is expensive. There is a continuous mist of cold water sprayed into
the extraction system that emulsifies the fats and causes it to drop into a collection trough.
Ultra Violet UV-C - The latest technology for the efficient elimination of grease from within
kitchen ventilation systems is the combination of Cartridge filters and Ultra Violet UV-C light.
This will give grease and odour removal efficiencies in excess of 98%.
The large amount of grease drawn into a kitchen ventilation system creates a fire risk. One
of the most common causes of commercial kitchen fires is through sudden combustion of
grease-laden air in the extraction system. It can happen very quickly with no obvious cause
to the kitchen staff. Where more than moderate grease extraction is happening, a fire
suppression system needs to be built into the ventilation system.
Most fire suppression systems use either wet or dry chemicals that are activated
automatically in the event of a fire, which originates in any one item of cooking equipment.
In the event of a fire in the ventilation system, there should be a trigger mechanism that
shuts off gas and electricity supplies to prevent making the fire worse. The Association of
British Insurers has produced a Fire Risk Assessment document for kitchen ventilation
Cleaning of extraction systems is essential on both hygiene and fire safety grounds. If there
is a high level of frying within the kitchen the essential cleaning may be as frequent as
weekly. The kitchen designer or installer will advise on the frequency of cleaning. Failure to
follow laid-down ventilation system cleaning routines could render insurance invalid in the
event of a kitchen fire.