It's not all hot air
While some "slaving over a hot stove" in the kitchen is inevitable, there are growing health and safety concerns about working in a hot, steamy, grease-laden environment.
There are three types of risk: to personal health, to food hygiene and to third parties. In all cases efficient ventilation is needed, expelling fumes while bringing in fresh, clean air for comfortable, safe working.
An information sheet from the Health & Safety Executive (HSE), Ventilation of kitchens in catering establishments gives extensive advice on good ventilation practice. This is fairly complex, as removal of "used" air and fumes must be balanced by introducing fresh air, which must come from "clean" areas and cause no uncomfortable draughts.
Carbon monoxide poisoning from incomplete combustion is a well-known risk. Less well known and while not lethal, a carbon dioxide build-up above 1,000 parts per million from complete combustion of gas can cause headaches, drowsiness and loss of concentration, with consequent dangers.
Complementing the HSE advice are publications from the Heating & Ventilating Contractors Association, Standard for kitchen ventilation systems and Guide to good practice, cleanliness of ventilation systems.
The HSE recommends canopy overhangs of 250mm to 300mm for island extractors and, for wall-mounted extractors, 250mm at the front and 150mm either side. However, ranges vary and you may need greater overhangs in very hot zones.
Systems must comply with British Standard BS6173:2001, which requires interlocking of mechanical ventilation systems and gas supplies for all types of commercial kitchen appliance, preventing a gas appliance from being switched on before the ventilation system is operating.
Besides evacuating fumes, systems need to avoid a build-up of grease in ducting, and prevent insect pests from being drawn in with replacement air.
Most cooking oils flash off inflammable vapours above 200ºC, and this flashpoint reduces with oxidation from repeated use, while differing cooking styles produce different mixtures of grease and vapour.
Prevention of grease accumulation is very important. If not addressed, it provides a feeding ground for bacteria and insects and also accelerates fires.
Many grease filtration options are available, and both filter replacement and easy cleaning are key considerations. Fire suppression systems can also be built into hoods.
Filtration, however, is only fully effective in conjunction with regular maintenance, and performance can be enhanced through choice of hood type.
The HSE recommends a kitchen ventilation rate of at least 17.5 litres per square metre of floor area, or 30 air changes per hour.
This is fine in summer, but not in winter when more controllable ventilation may be desired.
A basic hood will extract a given volume of fume-laden air, together with its heat, but induction hoods partly separate fume extraction from ventilation. They draw in fresh air for high-velocity discharge into the hood, which creates a low-pressure zone over the work area and helps to extract fumes via the hood and filters.
Only 20 per cent of extracted air comes from the kitchen, so energy is conserved, although induced air can also be used for ventilation as required.
Using atmospheric air in this way improves filtration efficiency as the bulk gas temperature is lowered, helping suspended grease condense on filter elements.
Induction hoods offer more control over kitchen heating and ventilation but, whichever system is chosen, it pays to work with experienced suppliers and installers who are familiar with the latest standards, regulations and guidance.
- Steve Leonard is managing director of Ledaire Fabrications. Tel 020 8684 0197 or email ledaire@btclick. com
