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The following information is provided
courtesy of The Catering Equipment Suppliers Association.
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 the
vicinity.
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 replaced.
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
extracting grease.
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%.
Fire risk
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
systems.
Cleaning
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.
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