Towards safer and more comfortable commercial kitchens
STEVE LEONARD advises on standards, guidance and product selection for the effective, efficient and safe ventilation of commercial kitchens.Catering can be highly rewarding, but while some ‘slaving over a hot stove’ is acceptable, there are 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 to expel fumes and bring in fresh air for comfortable and safe working. Extensive guidance
HSE information sheet ‘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. While less well known and not lethal, a carbon dioxide build-up above 1000 ppm, 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. DW/171 is a ‘Standard for kitchen ventilation systems’, while TR/17 is a ‘Guide to good practice, cleanliness of ventilation systems’. The HSE document recommends canopy overhangs of 250 to 300 mm for island extractors and, for wall-mounted extractors, 250 mm at the front and 150 mm either side. However, ranges vary, and we regularly advise greater overhangs in very hot zones. Systems must also comply with British Standard BS6173:2001, which requires interlocking of mechanical ventilation systems and gas supplies for all types of commercial kitchen appliance to prevent a gas appliance being switched on before the ventilation system is operating. Besides evacuating fumes, ventilation systems need to avoid a build-up of grease in ducting and prevent insects being drawn in with replacement air. Most cooking oils flash off inflammable vapours above 200°C, and this flashpoint reduces with oxidation from repeated use. Differing cooking styles produce different mixtures of grease and vapour. Filtration
Prevention of grease accumulation is very important to avoid providing a feeding ground for bacteria and insects and also accelerating 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 with choice of hood type. HSE recommends a kitchen ventilation rate of at least 17.5 l/s/m2 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. Induction hoods partly separate fume extraction from ventilation. They draw in fresh air for high-velocity discharge into the hood, creating a low-pressure zone over the work area and helps to extract fumes via the hood and filters. Improves efficiency
Only 20% of extracted air comes from the kitchen, so energy is conserved, although induced air can also be used for ventilation. We believe using atmospheric air in this way improves filtration efficiency as the bulk gas temperature is lowered, helping suspend grease condense on filter elements. Induction hoods offer more control over kitchen heating and ventilation. However, 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 Ltd, Limes Place, Limes Road, Croydon CR0 2HA.