Things to consider when using LED light fittings in hazardous areas

The EU has set itself ambitious energy-saving targets. Regulation 2019/2020/EU laying down ecodesign requirements for light sources has made the requirements for lamps far more stringent – with the result that conventional T8 fluorescent lamps in lengths of 600, 1200 and 1500 mm will no longer allowed to be put on the market from 1st September 2023 onwards. From this point on, retailers in the EU will only be able to sell off their remaining stock. But as is often the case in life, there are exceptions to this rule too. The new EU directive defines these in Annex III. Exceptions for industrial companies and the process industry in particular include light sources and separate control gear which are used in hazardous areas or for emergency operation. However, this does not give them free rein. This is because, in accordance with the new directive, the fluorescent lamps used there also have to be "according to the legislation mentioned", including Directive 2014/34/EU (ATEX), and also have to be "specifically tested for the mentioned operating condition or application according to relevant Member States legislation".

While the defined exceptions aim to ensure that no untested lamps or lamps of insufficient quality are used, especially in sensitive applications, users also have to take market mechanisms into consideration in their spare parts planning. Industry should expect to see the price of the few still officially sellable light sources to rise sharply due to the dramatic drop in manufactured quantities. It's good to build up stocks of lamps. But it's better to have already planned or started the changeover to modern light sources.

Against this backdrop, a rapid shift to LED light fittings as a fully fledged alternative to fluorescent lamps becomes more appealing. Replacing fluorescent lamps with LEDs pays off in many different ways at once. The lower energy costs – an LED solution requires just around half as much electricity compared to a fluorescent tube light with comparable light output – are just one aspect, albeit an increasingly important one. If a company has set itself sustainability targets, replacing conventional luminaires with LED light fittings will soon achieve the desired outcome of reducing the electricity demand for lighting.

Something that is often overlooked when buying light fittings is that higher investment costs, like those incurred when using LED light fittings, usually account for the smallest proportion of costs over their entire life cycle. In the long term, maintenance costs are far more critical. The service life of fluorescent lamps is only one quarter to one fifth of the service life of comparable LED light fittings, while their luminous flux noticeably decreases during this period.

In most industrial systems, replacing lamps during system maintenance, particularly in hazardous areas, is a time-consuming and complex process. Fewer maintenance cycles for LED light fittings with a service life of between 50,000 and 80,000 hours mean huge cost savings for users. This is because a risk assessment has to be drawn up and appropriate protective measures taken each time a maintenance task is performed in a hazardous area. What's more, only specially qualified staff are permitted to plan and carry out work in hazardous areas – otherwise there could be liability issues. But there are still many aspects to consider when using LED light fittings in hazardous areas – which is why we've outlined the basics here.

LED light fittings are also a potential source of ignition: Electrical sparks, hot surfaces or optical radiation can supply the energy to ignite gas or dust atmospheres. In general, an explosion can take place if three factors are simultaneously present: A flammable substance, oxygen (air) and a source of ignition. If explosive atmospheres cannot be avoided, their ignition must be prevented (secondary explosion protection). If ignition can also not be avoided, the impact of the explosion must be limited to a safe level.

The requirements for electrical equipment in hazardous areas are specified in a variety of national and international regulations. Until recently, regulations for gas hazardous areas were defined in standard series 60079, and for dust explosion areas in series 61241. Since many of the requirements were the same for both areas, the two standard series were combined under IEC 60079. The different ways of ensuring explosion protection for electrical equipment are called "types of protection". These are specified in separate parts of IEC 60079.

To work out the required protection level in a system, operators have to classify the work areas in the system into zones according to the severity of the explosion hazard. For this purpose, the probability of occurrence, frequency and duration of potential explosion hazards are usually assessed. These criteria are used to distinguish between the three Zones 0, 1 and 2 (combustible gases and vapours), as well as Zones 20, 21 and 22 (combustible dust), with 0 and 20 representing the greatest explosion hazard in each group. The Ex zone then results in the required device category for the light fitting. Device categories define the level of safety achieved by the device (1: Very high, 2: High, 3: Normal). The letters G or D which follow in the device designation stand for gas or dust.

When choosing devices for use in hazardous gas atmospheres, the temperature class and the device subgroup (IIA, IIB, IIC) are required, while the maximum permissible surface temperature and the device subgroup (IIA, IIB, IIC) are essential for explosive dust atmospheres. Complying with the temperature class (T) and the max. permissible surface temperature ensures that the light fitting's surface temperature is below the ignition temperature of the explosive atmosphere.

There is a crucial difference between fluorescent lamps and LED light fittings: With fluorescent lamps, the air in the enclosure acts as a thermal isolator, while the heat produced by LED light fittings has to be conveyed to the outside as quickly as possible to limit the surface temperature at the enclosure. This has had far-reaching effects, including the development of compact LED tubular light fittings.

The temperature of the LED light fittings is not only critical for explosion protection, it determines their service life too. LED chips and electronic balast are thermosensitive, which means that their service life decreases as the temperature rises. A rule of thumb is that a 10 K increase in temperature halves the service life. Since compact LED technology makes it possible to design ever smaller light fittings, the thermal path to the electronics is shorter. This is why effective temperature management, which is implemented in the design and in sophisticated control electronics, is important when designing LED light fittings.

Service temperatures up to +60 °C are generally not a problem. The latest innovations, such as the 6036 LED tubular light fitting from R. STAHL, can even be operated up to +70 °C and still last for 100,000 operating hours. This is not only important in systems where the light fittings are exposed to heat sources due to the operation conditions, but also in regions with extreme climates, such as the Middle East.

As previously mentioned, the long maintenance cycles are a compelling reason to switch to LED light fittings. LED technology is not only advantageous due to its long service life, it also offers the option to automate monitoring tasks. Since light is relevant to safety for systems in the process industry, lighting needs to be inspected on a regular basis – or even weekly for emergency luminaires. Manual inspections can be replaced by digitalisation using the digital addressable lighting interface (DALI), which is standardised in accordance with IEC 62386. This not only makes it possible to control light fittings individually, but also to constantly monitor them. In addition to replacing inspections, this also offers the option of defining individual maintenance cycles and planning maintenance dates for each light fitting. R. STAHL's latest tubular light fitting – the 6036 – not only has a digital DALI interface option, it can also be dimmed to 50% using an optional second switching phase. What's more, a variety of different emergency lighting scenarios can be configured very easily by means of a central battery system in conjunction with an address module in the tubular light fitting.