In terms of the services and system design, particular consideration should be given to the specific areas of gas safety as well as overall ventilation requirements.
This CPD will consider commercial kitchen gas safety, focusing on methods that may also save energy by controlling ventilation without compromising air quality.
Ventilation
The appropriate British Standard (Specification for the Installation of Gas-fired Appliances for Use in all Types of Catering Establishment, BS 6713[1]) states that ‘catering areas shall be ventilated to provide air for combustion and removal of combustion products and steam, etc, from the working operation’.
This is to ensure not just a comfortable atmosphere but also that the by-products of the cooking process do not adversely affect the kitchen’s occupants.
For example there are carcinogenic pollutants, Polycyclic Aromatic Hydrocarbons (PAHs), that can be present in the air as a result of cooking food and hot oil. So it is important to ensure adequate ventilation for health reasons, as well as sufficient fresh air to enable complete combustion, and for the general comfort of the staff.
It is also essential to provide adequate make-up air for gas-fired appliances, as the lack of an adequate supply of air, and/ or correct flueing arrangements can lead to incomplete combustion and the accumulation of combustion products such as carbon monoxide[1].
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.
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Ventilation systems and gas supplies should be interlocked to ensure safe environments
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.
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, eighthour time-weighted average with a shortterm 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 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.
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An example of a simple single control panel that provides fast feedback
Typically, such a panel would also be able to monitor both carbon monoxide (CO) and atmospheric gas levels (ie methane and LPG). The system should be fitted with an on/off switch as well as being able to take a signal from one or more emergency gas isolation buttons. This panel may be capable of communicating with a building management systems (BMS) system to provide feedback of the kitchen’s operational status.
Gas safety proving
The supply of gas into the kitchen needs to be controlled and monitored safely. One of the practical issues is having confidence in the integrity of the gas supply pipework and appliances in the kitchen area.
BS 6173 states that where a solenoid valve is used, and where appliances are not fitted with a flame supervision device, there should be a means of proving that all the appliances are turned off before gas is allowed into the kitchen.
The Institution of Gas Engineers and Managers (IGEM) document, Strength testing, tightness testing and direct purging of small, low pressure industrial and commercial natural gas installations IGE/UP/1A[5], states that the closure of an electronic control valve (ECV) on a gas supply can result in the complete loss of pressure on the downstream side of the valve.
This would then necessitate a tightness test, and possibly purging (in large installations) before the resumption of the gas supply.
This could happen even where flame safety type devices are fitted to equipment, since they can continue to allow gas flow for up to 10 seconds following the closure of the ECV, resulting in a loss of gas pressure downstream of the ECV.
A drop in the downstream system pressure may also occur during periods when cooking is not taking place (eg overnight or at weekends) when, due to the allowable leakage rate on a given installation, the gas pressure downstream of the valve may drop significantly (although within the allowable pressure drop for the installation).
Gas pressure proving provides a means of ensuring that all gas appliances are switched off before allowing gas into the kitchen. It also ensures that no gas is escaping from the pipework or the appliances, so ensuring the integrity of the installation.
There are two principal methods of monitoring the gas proving. Differential pressure sensing is the more recently exploited method. This technique measures the pressure differential across the inlet and outlet supply of the ECV – rather than just the supply as with the other methods – hence the incoming gas pressure is not critical to the system operation. This, in turn, eliminates nuisance tripping.
This method will also isolate the gas supply from the kitchen if the gas drops to a dangerously low pressure during use.
However, as differential pressure monitoring takes varying supply pressures into consideration, it will not close the solenoid valve for transient changes of gas pressure, as may happen with other methods. This is known as a ‘dynamic’ means of gas proving.
Older designs that rely on allowing a timed amount of gas through into the downstream pipework for a set time period are static in operation and so can miss small gas leaks.
For example, if the incoming gas pressure is slightly higher than when the system was installed, it would mean that more gas than anticipated could pass through the small valve in the set time period – hence a small leak may not be identified.
Systems for communications and control
Single control panel solutions that provide fast feedback are available and relatively simple to use.
They typically incorporate an LCD display to give instruction and clear guidance to the kitchen operative. Such systems can monitor CO2 levels, as well as temperature, for controlling the ventilation to optimise energy consumption by controlling fan speed, and hence fan power and energy used to heat the air on cooler days.
They can also isolate the gas supply in the event of fan failure or if the CO2 level exceeds prescribed limits. The integrity of the gas installation can be checked automatically each time such a panel is switched on by utilising pressure differential technology.
Natural and LPG gas, CO2 and oxygen depletion detectors can also be incorporated into such controls panels where necessary.
Conclusion
The drive for safety combined with energy efficiency and the need to improve the working environment has led to very high expectations in kitchen design and operation. Instrumentation design and functional capabilities have advanced greatly in the last few years to provide monitoring and control solutions that are simple, reliable and integrated.
However the monitoring of the air for safety and quality can only be used to support systems that have been correctly designed, installed and regularly maintained.
© Chris Dearden and Tim Dwyer 2010
- BS 6173/2009/11.1 Specification for the Installation of Gas-fired Appliances for Use in all Types of Catering Establishments. BSI, 2009
- PD CEN/TR 1749: 2005, European Scheme for the Classification of Gas Appliances According to the Method of Evacuation of the Combustion Products (Types), ISBN 0580481034. 2005
- DW172: Specification for Kitchen Ventilation Systems. Heating and Ventilating Contractors’ Association, 2005
- Gas safety in catering and hospitality – Catering Information Sheet No 23 (rev1). HSE, 2007
- IGE/UP/1A Edition 2 Strength testing,tightness testing and direct purging of small, low pressure industrial and commercial Natural Gas installations. IGEM, 2005