Standards and guidance publications relating to gas use are changing at an increasing frequency. Some of these documents relate specifically to education premises – though most apply to a wider range of buildings. This CPD focuses on the area of gas safety in education buildings, and refers to current UK standards and guides.
Gas is used in three main areas within an education building:
• Boiler room for gas-fuelled boilers and water heaters
• Preparation of food within the production kitchen
• Classroom applications, such as in science laboratories.
Access to the first two areas is limited to staff and service personnel, but the third group is likely to present the greatest uncertainty and risk, as these – by their nature – are accessible to ‘non-competent’ persons.
Laboratories
Teacher control of the gas supply in a laboratory is the most effective way to ensure maximum gas safety and teachingtime efficiency. This can be done using a panel fitted behind the teacher’s desk that includes a key switch and emergency stop button to control an automatic isolation valve (AIV) .
IGEM/UP/11 Edition 2 (UP11.21), published by the Institute of Gas Engineers and Managers (IGEM), sets down the minimum safety requirements in educational establishments for designers, operators and users. This requires (section 6.2.4.1) that ‘where an AIV is required, the system shall include a downstream integrity check before the valve can be reopened’. A practical way to achieve this is by a gas pressure proving system; this will ensure that all gas taps are closed before allowing the use of gas
UP11.2 (section 6.2.2-3) requires that an ‘additional emergency shut-off valve should be fitted in a readily accessible position for use by teaching and technical staff’, and continues: ‘Where it is not practicable to install a manual isolation valve in a readily accessible position, or where it is required to interlock the gas supply with other safety systems – such as air flow, fire or gas detection – then an automatic means of isolation shall be installed.’
Food technology
Some form of mechanical ventilation will normally be incorporated into the design of a food technology area, to supply fresh air for the occupants and to ensure complete combustion of gas. Any mechanical ventilation should be interlocked with the gas supply such that, in the event of a fan failure, the gas supply will be isolated, as described in BS6173/20092 (section 11.1).
A food technology area will normally have a number of domestic-style gas cookers around the room, so it can be difficult to incorporate a cost-effective ventilation solution to remove both the products of combustion and the byproducts of cooking efficiently.
IGEM UP11.2 (section 11.2.4) takes this potential issue into account and states that, where the ventilation requirements might not be met, a carbon dioxide (CO2) monitoring system should be installed. CO2 monitors should have a warning alarm at a level of 2,800ppm, with 5,000ppm being the level at which the gas must be isolated.
Solutions for teaching and food technology areas would be to install a control and monitoring panel by the main teaching area, to ensure the integrity of the gas supply and equipment by use of gas pressure proving. Such devices can also include the facility to isolate the gas in the event of a high CO2 level or ventilation-fan failure. A gas pressure proving system for use in a teaching area should be fitted with an emergency gas-isolation button on the panel, as well as a key switch to control gas availability at workbenches. A countdown timer should also be incorporated, to ensure that gas is not available for out-of-hours, unauthorised use.
A well-designed gas pressure proving system ensures that there is no pressure drop downstream of the control valve – that is, no leakage or open appliances – before allowing gas to flow. Two main methods of gas pressure proving are available: 1) Single-mounted downstream sensor: This method is assumptive, because it takes a snapshot of the gas pressure upstream of the safety shut-off valve (SSOV) when it is first opened, and then looks downstream of the (subsequently) closed SSOV for a pressure drop. Consideration should be given as to whether it is acceptable for a safety system to be assumptive in its design, in view of more recent technological advances towards fail-safe operation. An example would be that, if the gas supply pressure was too high, for whatever reason – for example, because of a failed regulator – then the valve should not be opened at all, as to do so could create a dangerous situation. Single-sensor systems are not fail-safe where there is an installation problem with the SSOV and a gas leak exists. 2) Differential pressure sensing. The other, more recently exploited, method of monitoring the gas pressure is by means of differential pressure measuring. This technique measures the pressure differential across the inlet and outlet of the solenoid gas-supply valve. This provides continuous pressure readings – effectively, during and after the pressure test – so ensuring an accurate safety check is carried out with no assumptions during the testing time. Such a system can constantly monitor the supply pressure without opening the SSOV – and is fail-safe where a gas leak is also present. Systems that monitor CO2, CO and combustible gases – as well as controlling the occupancy scheduled ventilation rates, bench water supply and electrical isolation – are available in a single control panel.
Boiler house and plantroom application
Gas detection should be fitted in all new and refurbished boiler rooms where the boiler house forms part of, or is attached to, the main building, as discussed in Building Bulletin 1003 (3.1.8) and IGEM UP/11. In the event of a genuine fire alarm, both the gas and the electricity supply to the boiler house should be isolated. If an automatic proving device (that is, gas pressure proving) is fitted, then automatic restarting is allowed after an interruption to the building electricity supply. This has a particular advantage – for example, in minimising the potential of pipes freezing after a power-cut during unoccupied weekends and holidays.
IGEM/UP/1A Edition 24 requires ‘the closure of a valve, for example, the electronic isolation valve (AIV), can result in the complete loss of pressure which necessitates tightness testing and purging before resumption of supply‘. This means that if, for whatever reason, the valve closes, a gas tightness test – and, on very large installations, purging – may need to be carried out before reopening the valve. Practically, this means that, if the gas pressure has dropped to 5 mbar or less, there is a requirement to test for tightness. A gas-proving system would be able to make this test at a push of a button; the alternative is a physical test by an engineer.
Combined gas-detection and pressure-proving systems, designed specifically for use in education building boiler rooms, are available. Combustible gas and carbon monoxide detectors can be connected to such a system, so that – in the event of detecting high levels of either gas – the gas supply would be isolated. An output to a building management system or a visual indicator, such as a flashing beacon, can be mounted outside the boiler room. Otherwise, in the event of the gas being isolated, the building heating and hot-water systems will not operate – potentially resulting in lost teaching time.
The system should be able to isolate the gas in the event of a genuine fire alarm. The system should also have provision for the connection of heat detectors, as referred to in BB100 3.1.8. Any system should be capable of differentiating between a power loss and a potential emergency isolation, so that a subsequent auto restart can be allowed safely.
Figure 1: An example of a gas proving system suitable for use in a boiler plantroom
Catering kitchens
The production kitchen in an education building is a commercial kitchen within the scope of BS6173:2009. It requires the interlocking of any mechanical ventilation systems – including supply air fans – with the gas supply in the kitchen. This includes mechanical extract systems that are not over the main cooking area, but are in the same room, such as a gas-fired steamer with an extract canopy fitted above. If this steamer extract fan is not interlocked then, if it is not Figure 1: An example of a gas proving system suitable for use in a boiler plantroom Figure 2: Example of control panel that could be located adjacent to teacher’s area in laboratory CIBSE Apr15 pp23-26 CPD Supp v3.indd 24 20/03/2015 11:46 www.cibsejournal.com April 2015 CIBSE Journal 25 Turn over page to complete module switched on, air can be drawn down the steamer extract canopy along with the gas products of combustion. The air is then pulled across the occupied room by the main extract canopy. This is more likely where natural ventilation is used for make-up air.
Figure 2: Example of control panel that could be located adjacent to teacher’s area in laboratory
Catering kitchens
Secondary interlocking via CO2 monitoring as part of an interlock package is not allowed in BS6173:2009, as it is considered to be an interlock override. Fixed CO2 monitoring can form part of the ventilation interlock package, as discussed in IGEM/UP/19.15 (section 5.1.2). This is to monitor the free kitchen environment, so the sensors should not be fitted under an extract canopy. For new installations, the maximum allowable level of CO2 is 2,800ppm, and for existing installations 5,000ppm. The gas supply should be isolated if the CO2 reaches these levels.
CO2 levels may also be used as an indicator of air quality in the kitchen, and can give an early indication that the ventilation is inadequate or failing – for example, due to dirty extract hood filters. IGEM/UP/19 Edition 1 Design and application of interlock devices and associated systems used in association with gas appliance installations in commercial catering establishments has recently replaced the withdrawn Gas Safe Technical Bulletin 140 (TB140).
Flame-safety devices on cooking appliances can take up to 10 seconds to close. This can result in partial, or complete, loss of gas pressure after the closure of an upstream AIV, for whatever reason.
Therefore, a gas pressure proving system can usefully form part of any interlock package, allowing for a more practical system restart to comply with the requirements of IGEM/ UP/1A Edition 2, as discussed previously. The disengagement of flexible hose bayonet connectors in kitchens can also lead to pressure loss in the distribution pipework.
Systems are now available that carry out the functions of interlocking the ventilation with gas supply, proving the gas cook line gas tightness of the appliances, as well as monitoring the carbon dioxide level in the atmosphere. Where required, such a system can also adjust the ventilation rates, depending on the amount of activity in the kitchen, by monitoring the CO2 levels and the kitchen temperature.
As long as the ventilation system has been correctly specified, then the installation of a good-quality safety and monitoring system as described will ensure comfort and maximum safety in the kitchen. Using integrated displays, these panels can provide the users with quick-reference visual indication of the state of the system, the environment, and the gas status.
Figure 3: Ventilation in catering kitchens can be interlocked with gas proving systems
© Chris Dearden and Tim Dwyer, 2015.
References
- IGEM/UP/11 Edition 2 Gas installations for educational establishments, IGEM 2010
- BS6173:2009 Specification for the installation of gas-fired appliances for use in all types of catering establishments (2nd 3rd family gases), BSI 2009.
- Building Bulletin 100: Design for fire safety in schools, DCSF 2014.
- IGE/UP/1A Edition 2 Strength testing, tightness testing and direct purging of small low pressure
industrial and commercial Natural Gas installations, IGEM 2005. - IGEM/UP/19 Edition 1 Design and application of interlock devices and associated systems used
in association with gas appliance installations in commercial catering establishments’, IGEM 2014.