The publication of the engineering Standard IGEM/SR/25 Hazardous area classification of natural gas installations led to the publication of IGEM/UP/16 to provide practical advice to the industry.
Nine years after the initial enactment of these Regulations in 2003, most of British industrial and commercial companies, designers and installers are unaware of the implications of the Dangerous Systems and Explosive Atmospheres Regulations. DSEAR is retrospective for all flammable gas installations in factories, hospitals, shopping centres, shops and central plant in blocks of flats.
Each installation must be considered for the likelihood of a gas leak occurring and it is a legal duty for employers to consider the risks and control measures in place to mitigate against such leakage.
A risk assessment will need to consider the initial design specification, construction standards, local ventilation provisions, testing procedures and ongoing maintenance.
Much of this is covered in the Institution of Gas Engineers and Managers non-domestic procedures: UP/1 Strength, tightness testing & purging; UP/2 Installation of pipework; UP/10 Installation of flued gas appliances.
What is new is IGEM UP/16 Hazardous area classification for Natural Gas installations downstream of primary meter installations, for systems not exceeding 2 bar. Most gas installations operate at pressures below 100 mbar and it is simple for a competent person to ensure compliance.
Electrical components and other ignition sources, such as hot surfaces, all provide a means of igniting a leakage of flammable gas.
The HSL test work has determined what are reasonable leakage potentials and what ventilation is needed to dilute them to a safe level. SR/25 provides advice on the safety distances and volumes contained within the hatched area.
Any ignition source inside this volume has to be classified for use in a hazardous area. Such equipment is often called Explosion Proof and is more expensive than normal electrical equipment. It will be marked with something like EEx n IIB T2 as well as the Ex hexagonal logo.
The leakage size determined for low pressure pipework systems should generate a Zone 2 classification but can be designated as Zone 2 Negligible Extent (NE) where the use of standard electrical equipment is permitted.
If the same leak was in a space that was not visited more than six-monthly, was never maintained or had poor ventilation, then Zone 2 electrical equipment might be required. The Standard covers all methane-based gases with an SG below 0.8 for LPG.
New systems must be designed to take account of DSEAR. In existing systems, engineering judgement will be key and in most cases GEA can propose easy-to-apply solutions.
To achieve Zone 2NE, adequate local ventilation around every threaded or mechanical joint or potential leakage source is necessary. Local congestion will normally restrict the availability of ventilation and may preclude the use of a Zone 2NE classification.
Changes cannot be made to any pipework installation or local environment that may impact the Zone assessment. DSEAR requires a risk assessment be completed of the various parts of the downstream gas installation.
The smaller leak rate for below 100 mbar systems should always be able to achieve Zone 2 NE classification, provided they are located in a ventilated environment and most importantly have a maintenance programme. Where mechanical ventilation is employed for zoning, it must be interlocked with the gas supply.
Barrie Church is director of Global Energy Associates