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BS 6173 requires that appliances shall be interlocked with, ‘any mechanical ventilation that is fitted to enable their safe operation’. This means that all fans in the kitchen, including those more normally associated with the removal of vapours and fumes from the cooking process itself (for example over a steamer), need to be interlocked with the gas supply. Hazardous situations may arise if the products of combustion are drawn across a kitchen and taken up by the main extract hood because an extract canopy over a steamer is not switched on or interlocked with the cooking equipment controls. The ventilation requirements for specific
kitchen appliances may be determined from the European Scheme for the Classification of Gas Appliances According to the Method of Evacuation of the Combustion Products, CEN CR 1749[2]
. Most appliances installed under canopy
systems are designed to operate without a flue (CEN CR 1749 Type A). Others, for example, including types of convection ovens and deep fat fryers, usually require connection to a dedicated flue system (CEN CR 1749 Type B). Due to the possible adverse effect on flue performance many manufacturers permit the installation of Type B appliances without the use of the flue, but under a canopy. Therefore, the canopy/extraction system
is performing the same function as a flue system. The Gas Safety (Installation and Use) Regulations 1998, (GSIUR) Regulation 27(4) deems this as a ‘power operated flue’ system and requires an interlock, which will shut off the gas supply to such appliances in the event of an air movement failure.
Demand-based ventilation
Properly designed and implemented automatic, demand-based control of the ventilation rate linked to the level of cooking activity can be a means of saving energy whilst maintaining appropriate internal conditions. Minimising the energy used by the fans in the kitchen can be achieved by measuring the level of carbon dioxide (CO2
) and the room
air temperature. Monitoring the internal kitchen environment can allow for seasonal temperature variations, and automatically takes account of any stand-alone appliances such as electrically powered fryers in the cook line or in the surrounding area. Other methods of automatically controlling
the ventilation rate, such as measuring gas flow, may be less effective since they provide an ‘open loop’ control mechanism where the actual working environment is not monitored.
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CIBSE Journal June 2010
A minimum extract level should always
be set for the speed controllers so that, even when there is minimal cooking activity, an acceptable ventilation rate is maintained. Specific guidance on extract and supply air flow rates may be found in DW172, the HVCA specification for kitchen ventilation systems[3]
.
Monitoring and maintaining safe and good air quality
The Health and Safety Executive (HSE) catering sheet 23 revision 1, allows a maximum CO2 level of 2,800 parts per million (ppm) in the kitchen atmosphere. The occupational exposure limit for CO2
in the atmosphere is 5,000 ppm, eight- hour time-weighted average with a short- term exposure limit of 15,000 ppm over 15 minutes (HSE Workplace Exposure Limits EH40/2005). As a comparative reference, BS 6896
‘specification for installation of gas-fired overhead radiant heaters for industrial and commercial heating’, sets a limit of CO2 allowed in the atmosphere at 2,800 ppm; however, by comparison, the generally accepted normal guidance for comfort is 1,000 ppm. Considering that the ambient level of CO2
in
the outside air is between 350-400 ppm, a level of 2,800ppm in the kitchen would tend to indicate less than ideal ventilation. Carbon monoxide detection systems may
be installed. If installed, carbon monoxide detectors should give an audible alarm and be linked with an automatic gas shut-off system. This should be fail-safe and require manual intervention to restore the gas supply[4] Where CO and CO2
. sensors are used,
they should be specifically designed for use in commercial and industrial applications –
domestic versions should not be employed. For example, the domestic ‘traffic light’ sensors should not be used.
Interlock and monitoring solutions
The gas supply must be interlocked with the ventilation system using a gas solenoid valve (an electronic control valve) and this should conform to BS EN 161 Automatic shut-off valves
for gas burners and gas appliances. In 2007 the
Health and Safety Executive[4]
reported that
the requirement for interlocking specific equipment had been previously ‘largely overlooked’; however, the necessity for this had been reinforced through the unambiguous requirement in BS 6173. This interlock must not be fitted with a manual override function.
The drive for safety and efficiency has led to very high expectations in kitchen design and operation
The solenoid valve and the ventilation
system is normally linked through a control panel that would, for ease of access, typically be mounted close to the fan speed controllers. Such a panel would also monitor the CO2 levels both to ensure adequate ventilation and, combined with temperature monitoring, provide automatic adjustment of the ventilation rate for the comfort of the operatives. This system would also be designed to isolate the gas in the event that the CO2
level rises
above 2,800ppm. Typically, such a panel would also be able
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Ventilation systems and gas supplies should be interlocked to ensure safe environments.
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