The term ‘hazardous locations’ usually means an environment where atmospheric conditions make a fire or explosion possible – where a flammable vapour or gas (or a dust or powder) are combined with air or another oxidising agent.
“People hear ‘hazardous area’ and automatically think of oil and gas installations,” says Stuart Head, technical & compliance manager at Birmingham-based lighting specialist Petrel (pictured, right). He says that the firm does support big petrochemical installations – offshore LNG rigs, for instance – but also smaller and less predictable sites such as the ‘ammonia room’ of a supermarket food depot, agricultural grain stores and even warehouses in whisky distilleries, where alcohol evaporates through wooden barrels.
Head is adamant that the first stage is to carry out a risk assessment, and this is completely the responsibility of the site operator. Sometimes, he says, operators “didn’t realise that they had a hazardous area until they had an accident”. You can classify locations according to ATEX hazard zones (see box).
To be precise, the ATEX regulations no longer apply in the UK post-Brexit, and have been superseded by the UKEX regulations, formally, the ‘Equipment and Protective Systems Intended for Use in Potentially Explosive Atmospheres Regulations 2016’ which supersede the ATEX 95 Equipment Directive 2014/34/EU (a recast version of the earlier Directive 94/9/EC).However, there is a lengthy crossover period, and the two sets of rules are functionally identical for some time to come. Some items will need to be marked with the UKCA marking (replacing the CE mark in the UK) although this is not essential until the end of 2023.
The other marking you will see on ATEX- or UKEX-compliant equipment is the Ex mark: a yellow-filled hexagon with the Greek letters εχ (epsilon chi). This is also shared by the international IECEx regulations (again, functionally identical to ATEX). In the US, there are separate HAZLOC and UL standards.
Certification
“For our Zone 1 equipment, all of it needs to be certified by a third party on our behalf,” says Head. “The tests are quite arduous, such as impact tests, hot and wet testing, low-temperature testing – then another impact test. You can have two months of testing, and then they drop a weight on it and it’s failed.” The testing firms include ‘notified bodies’ such as SGS Baseefa and CSA Group Testing UK.
The aim of the ATEX and similar standards is to ensure that there is no source of ignition in a hazardous environment. “We employ various protection concepts on our products,” says the technical & compliance manager.
The term ‘flameproof’ is a US definition, he adds, which usually entails a flame path to allow vapour out. Instead, he says, “We like to prevent the explosion from happening in the first place.” This means eliminating the possibility of an ignition spark.
The ‘intrinsically safe’ approach doesn’t always work for lighting – it demands minuscule power levels inside the device – so the usual measure is encapsulation: “For instance, the LED driver [providing the low-voltage DC required for the LEDs] is encapsulated in non-conductive resin.” He won’t say what proprietary resin is in Petrel’s products, but typical materials include silicone and epoxy compounds.
In the specifications for a lighting product are certification codes such as: Ex II 2GD Ex eb mb op is IIC T4 Gb — Ex II 2GD Ex tb op is IIIC T135°C Db. These detail the protection concepts used, the temperature class and the types of gases or dusts that the unit can withstand. There is also usually an ingress protection code, such as IP66/IP67.
The temperature class or ‘T-Class’ (T1-T6 – see box, left) specifies the maximum temperature of a device, or, if it is dust-rated, its maximum surface temperature. This must be significantly lower than the autoignition temperature of materials in the environment. So for petrol – with an auto-ignition temperature of around 280°C – equipment should be rated at T3 (200°C) or better (T4, T5 or T6). But you also need to allow for the worst-case ambient temperature: +40°C is usually quoted, but some show the figures for +55°C, and a supplier should be able to give figures for higher ambient temperatures.
LED lighting (such as Petrel area light, left) has almost totally replaced fluorescent fittings. “The benefits of an LED far outweigh fluorescents,” says Head. They are more efficient, so put out less heat (Raytec LED Spartan bay lighting for Zone 1 and Zone 21 applications pictured above). But he also points out: “You cannot put any LED module in a fluorescent light fitting – you don’t know how much heat it will put out”. He says that Petrel underdrives its LEDs so they run cooler, meaning a longer life.
INSTALLATION
Installation is not just a matter of specifying the correct units: wiring and switchgear must be suitable, and installed by a competent electrician. This can be ensured by the CompEx (Competency in Ex atmospheres) certification scheme, a global standard for technicians (and designers) working in potentially explosive atmospheres, with modules covering different aspects.
“How you terminate wiring and make joins is very important,” says Stuart Head: the correct ATEX-rated terminal blocks, conduit and glands will minimise the risk of ‘arcing and sparking’. He also points out that rather than installing an expensive Ex-rated switch, often “it’s better to locate the switch outside the hazardous area altogether”.
“We do like to get involved at an early stage in the design,” he points out. “ATEX is important, but the real challenge is whether the light levels are right.” Standards for workplace lighting include EN 12464-1.
BOX: ATEX hazard zones
The Europe-wide ATEX regulations classify hazardous areas into discrete zones, which express the probability of there being a hazard, in the form of both a combustible material (such as gas or fuel vapour) and an oxidising agent (air).
Zone 0 means that the risk is always there – for instance, inside a fuel tank.
Zone 1 means that there will be a hazardous area present during operating conditions, such as when filling a car with petrol (Petrel 620 Zone 1 light at left).
Zone 2 means that under normal conditions there’s no risk, but if something goes wrong – say a tank ruptures or a valve fails – there can be a risk. The zone designations take a ‘2’ prefix if the hazard is in the form of dust or fibres rather than gas or vapour, so the equivalents are Zone 20, Zone 21 and Zone 22.