scope:

This Standard covers hazardous area classification for gas metering equipment.

This Standard applies to liquid-free Natural Gas (NG) with a combined proportion of methane-plus-inerts of greater than 89% by volume; a gross calorific value not exceeding 45 MJ m^-3; molecular weight not exceeding 20 kg kmol^-1; lower flammability limit (LFL) of not less than 4.4%; a temperature range of -20°C to 50°C and gauge pressure not exceeding 100 bar. Ambient temperatures are assumed to be in the range of -20°C to 35°C.

Note: This Standard does not apply to either compressed or liquefied NG (CNG or LNG) vehicle filling station installations. Guidance on the latter is provided by IGEM/UP/20 and IGEM/UP/21 respectively or the Energy Institute (see Appendix 2, Section A2.6).

A zone of negligible extent is only applicable in this Standard to those installations of MOP not exceeding 10 bar.

This Standard applies to any potential release of NG except those that may be caused by catastrophic failure such as the rupture of a process vessel or pipeline, component failure and similar rare events that are not predictable.

This Standard applies to primary and secondary meter installations and associated volume conversion equipment and all associated electrical equipment and connections, in industrial and commercial premises and which have been installed to BS 6400-1, BS 6400-2, IGE/GM/4, IGEM/GM/6, IGEM/GM/8 and IGEM/GM/5, as appropriate. These installations will also need to have been tested to and comply with IGE/UP/1, IGE/UP/1A, IGEM/UP/1B, IGEM/UP/1C as appropriate. However, it does not apply in the following circumstances when it will be necessary to use IGEM/SR/25:

• ventilation is of the forced type

• creep relief vents terminate within a meter installation's housing

• a competent person considers there to be unusual site circumstances

• the installation is at a remote, unmanned, site

• it is considered that leaks may go undetected

• unodorised gas is metered.

Note 1: DSEAR does not apply to meter installations installed in domestic premises. Therefore, it is not intended that this Standard be used for hazardous area classification in such circumstances.

For the purposes of this Standard, a meter installation in domestic premises is an installation within, or near to, a domestic dwelling into which the installation supplies gas and where it is reasonable to expect that the householder will be in the vicinity of the installation on a regular basis.

Note 2: For the purposes of this Standard, a meter installation in industrial or commercial premises is an installation within the boundary of the premises within which the gas load is located and where it is reasonable to expect that passers-by will be in the vicinity of the gas installation on a regular basis. This is to distinguish this type of installation from a remote site, for example a National Transmission System above-ground installation where it is reasonable to expect that persons will not be present for long periods of time and when IGEM/SR/25 will need to be applied.

Note 3: Some commercial premises utilise domestic style installations and housings. This Standard is applicable to such installations.

This Standard may be applied for meter installations in existing premises where ventilation is present but where it is difficult or impossible to confirm that levels of ventilation comply with current design Standards.

This Standard uses a methodology that assumes meter installations are protected from external interference and located in populated areas, or sites are manned in industrial and commercial premises. Such conditions will lead to a high probability of detection of any gas leak and within a short time period. Where these conditions apply, such installations can be deemed to be visited (with reference to IGEM/SR/25) on a regular basis.

All pressures quoted are gauge pressures unless otherwise stated.

Italicised text is informative and does not represent formal requirements.

Appendices are informative and do not represent formal requirements unless specifically referenced in the main sections via the prescriptive terms "must", "shall" or "should".