Providing a safe gas supply to flats in high-rise developments brings its own set of challenges. Barrie Church reviews how the IGEM Standard G/5 aims to ensure that the work is always done safely and correctly.
The work in IGEM on the standard G/5 was first started as part of a request for advice on gas installation designs in Hong Kong where their apartment blocks can be 36 floors or more. There is also a restriction on the location of gas pipes within the building and, as a result, the incoming service pipework is strung up the outside of the building. It is all screwed and leaks occur on the screwed joints, which are costly to repair so high up.
As in the UK, the Standard has to be written to allow for the ‘laws of the land’. It also has to reflect existing practice as well. For example, in the UK we may have a riser as a service pipe or as an installation pipe, and we have different approaches for both.
The worst high-rise building disaster in the UK was many years ago when Ronan Point in London collapsed following an explosion. As a result of this incident, many countries banned gas pipes and even gas in total from within high-rise buildings, and this is still the case in a number of EU countries.
One can never be 100% sure of the actual cause at Ronan Point, but a number of things came to light, highlighting that there was not really a problem with the gas pipework. Firstly, there were LPG cylinders in the vicinity and the rubber hoses were not firmly fixed with clips. Secondly, the gas cooker flex used a union and this appeared to have been over-tightened.
Lastly, and most importantly, the structure was extremely weak – any small incident could have led to failure.
Returning to G/5, instead of a simple scope dealing with the original issues, it grew during the public comment stages to cover maisonettes and flats above shops, and the term multi-occupancy buildings came into being.
During the preparation work, a risk assessment was performed and, as with Ronan Point, the issues of DIY and unauthorised interference were discussed. Clearly the failure to ignite the burners on a gas cooker was a real issue. At that time, there were few UK-built cookers with flame safeguard systems on them, and the UK manufacturers felt they needed time to incorporate them within their designs. Many EU manufacturers did, however, have such systems within their cookers.
Another important issue was that of the locations of the gas meter and its associated ECV. This is more of a Building Regulations matter, but the Standard has to deal with it with respect to means of escape in the event of fire. Meters may be remote, just external to the apartment or within the apartment. There may also be a central primary meter at ground level together with secondary charging meters at the apartment. In each case, the location of the ECV and AECV must be considered and specified.
Section 4 of G/5 covers planning from the point of view of the incoming network as well as the obligations of both the gas transporter (under Pipelines Safety Regulations) and the meter installer (under Ofgem MAMCop).
They need also to consider the movement (expansion/shrinkage/sway) of the structure in the design of their pipework. Clearly their pipework system will not be designed for the connected load, and they will apply a diversity factor, and the information on the design flow rate is given in Appendix 5 of IGE/GL/1. This is accompanied by a warning that care should be taken when estimating the design load when ten or fewer consumers are being supplied from a network pipeline or meter bank and/or where there is a possibility of large (e.g. 40kW input) combination boilers being installed.
With high-rise buildings, the effect of altitude may be used to advantage. Lighter-than-air gases will show an increase in actual pressure at higher levels due to altitude. This in turn means that a higher pressure drop may be used in the pipework. Equally, for very tall buildings it could well be necessary to ensure that the pressure is regulated at each floor.
The following formula is used:
Pressure change (mbar) = 0.123 (1-SG) x Height of building (m)
The final planning issue is one of access to the service riser for maintenance. Where access panels are used, their fire integrity and accessibility are of paramount importance.
Section 5 covers the issues of meter location in order to comply with the various UK Building Regulations.
Various figures in G/5 detail the differences between ‘common means of escape’, ‘common alternative means of escape’ and ‘common sole means of escape’. In summary:
- Meters cannot be sited on or under the stairway, or in any other part of the premises, where the stairway or that other part of the premises forms the common means of escape in case of fire, unless other measures are taken.
- Meters cannot be installed where the consequences of a gas escape, fire or explosion at the meter would compromise the integrity of the structure of the building.
- Meters must not be installed in any common sole means of escape nor in any room, box, cupboard, or other compartment or enclosure that opens onto a common sole means of escape.
- Meters shall not be installed in a meter room where twin fire doors create a false or intermediate lobby between the meter room and the common sole means of escape.
- Meters shall not be installed in any common alternative means of escape unless a risk assessment indicates it is safe to do so. It is suggested that a fire or explosion in one means of escape must not affect the escape of occupants of the building by the other means of escape, or that the means of escape is largely in the outside open air where any escape of gas would quickly and safely disperse. Another option is the use of an Excess Flow Valve and a Thermal Cut-off Valve in conjunction with other safety measures.
The topic of meter bank location ventilation is discussed at length in clause 5.4, and this topic is described in IGEM/GM/7A and 7B. This matter is a specialist topic area and is covered also by IGEM/SR/25 on hazardous areas.
Pipe entries and risers
Section 6 provides some very useful information and sketches for all pipe entries into buildings. Clause 6.3 gives detailed advice on below-ground entries, which may be more appropriate to taller structures and useful for non-domestic entries.
The risers will need to be suitably located, supported and protected against undue risk from accidental damage, tampering and vandalism. Above-ground steel pipework has to be protected against corrosion by the use of either an all-galvanised pipework system or a paint system that complies with BS EN ISO 12944 Paints and Varnishes.
BS EN ISO 12944 gives environmental categories C1–C5 dependent upon the location of the pipework – for example:
a. Pipes within habitable buildings – Category C2
b. Pipes within unheated external housings – Category C3
c. External pipes – Category C5
Installation pipework and appliances
There are few extra requirements over and above BS 6891 and IGEM/UP/2 for pipework in such buildings. UP/2 includes additional requirements for high-rise buildings. Compression fittings are not permitted within a means of escape.
Equally, there are additional requirements for appliances. However, Section 8 contains details covering boiler plant rooms (Energy Centres) and the need to ensure any residual risks are controlled and designed out following a risk assessment. The safety issues highlighted by the Dangerous Substances and Explosive Atmospheres Regulations will also be relevant for such plant (see IGEM/UP/16).
Domestically, where a gas cooker is to be installed into an internal kitchen, ventilation has to be provided in accordance with appropriate Building Regulations and in accordance with BS 5440-2. Flueless appliances are required to have a flame supervision device (FSD) fitted to each burner (except for cooker oven burners of uncontrolled heat input less than 0.6kW). Devices that only attempt to automatically re-light the burner do not meet this requirement.
Appendix 3 provides detailed information on the content and scope of the necessary risk assessments that are particularly relevant to such structures. The important issue is that any problems raised by an assessment are considered during the design as part of hazard reduction.
This process is referred to as mitigation, and the aim is to reduce the significance of the risk issue – ‘As Low As is Reasonably Practicable’ ( ALARP). For further guidance, see the HSE Publication: Reducing Risks, Protecting People; HSE’s Decision Making Process.
The provision of good ventilation in confined locations is essential in order to dilute and disperse any small leakages. Equally, good maintenance and regular inspection of systems will minimise the potential for the leak to occur in the first place. Many energy centres rely on a mix of mechanical and natural ventilation, and it is essential to ensure that the ventilation system and grilles are kept free of debris and fully interlocked with appliance operation.
To Sum Up
- Properly designed, installed and maintained gas installations have rarely caused explosions in multi-occupancy buildings. Then issues of DIY, poor maintenance and even vandalism must be considered.
- Safety issues relating to means of escape and fire control impinge onto the design and location of meters, pipework and appliances.
- Domestic cooking appliances need to be fitted with flame safeguards as a precaution against them being accidentally being turned on and not ignited.
- Maintenance of all parts and aspects of the installation is imperative.
- The correct preparation and interpretation of risk assessments is vital to ensure safe design.