Luminaires for industrial and hazardous environments

Industrial environments can pose significant challenges to the safety and effective operation of lighting systems. Luminaire selection and system design must meet performance goals where mechanical strength, weight, thermal, electrical, corrosion resistance, hazardous environment and water and dust ingress requirements must be considered. Designers must gain a firm understanding of all environmental factors that can cause system failures to deliver ‘environmental compatibility’ of lighting.

Many industrial facilities present harsh environments in which luminaires are expected to function. Chemicals, fuel and pollutants within the operating environment of the luminaire need to be considered when choosing a fitting. For example, a spray-painting booth containing chemical thinners would quickly deteriorate plastics, so a metal luminaire with glass diffuser would be a more suitable choice. In a chemical factory, refinery or areas exposed to salt water, the electrical equipment could be subjected to chemical agents that can cause corrosion of the luminaire materials, rendering metal-cased luminaires as inappropriate. In these applications, fibre-reinforced-plastic enclosures may provide better service life.

Failure to properly consider the environment into which the luminaires will be placed, as well as the luminaire material properties, can result in mechanical breakdown of the luminaire and failure of electrical insulation, presenting an electrical hazard to personnel and even ignition of flammable gases or dusts, due to a breakdown of the enclosure.

The use of chemical surface treatments (conversion coatings and anodisation), as well as corrosion-resistant primers and topcoats, will provide barriers or ‘sacrificial-corroding’ layers to protect the base materials and may need to be specified.

The surface finish of luminaires is also important, as smooth, polished surfaces reduce the amount of chemicals and salts that can accumulate on the surface of the luminaire, leading to pitting.

In industrial facilities, luminaires are often exposed to water in various processes or clean-ups, subjecting them to moisture and, in some cases, high-pressure water hoses. In these situations, consideration of the IP rating (water and dust ingress) of the luminaire, in accordance with AS/NZS 60529, must be paramount to prevent ingress of water into it. Even with correct IP-rating specification of the luminaire, harsh environmental conditions can cause degradation to the point where moisture and dust can penetrate.

Where luminaires may be subject to mechanical impact, suitable impact protection must be considered. EN62262 specifies an IK-rating system, whereby luminaires are subject to mechanical impact. The higher the IK rating, the higher the mechanical impact it can withstand. Again, while it may have a suitable IK rating, exposure of the material to harsh chemicals, UV and extreme temperature variations can deteriorate the luminaire’s mechanical properties.

Electrical equipment that is to be placed into service in a hazardous area must conform with AS/NZS 60079 for hazardous gas environments and AS/NZS 61241 for hazardous dusts, fibres and ‘flyings’. As Australia is a member of the IECEx scheme, we can accept luminaires that comply with European standards IEC 60079 or IEC 61241. It should be understood that all equipment certified for use in hazardous areas must be labelled to show the level of protection offered. It must also be noted that compliance with these standards does not indicate compliance with the mandatory electrical safety requirements for electrical equipment.

Electrical equipment in Australia must comply with the basic safety requirements of AS 3820. In addition, it is recommended that luminaires in industrial environments also comply with the safety requirements of AS/NZS 60598.1:2003, with thermal testing carried out at a minimum of 40 °C to ensure satisfactory safety compliance at high ambient temperatures. The ambient temperatures in industrial plants, particularly in Australia, can see luminaires exposed to air temperatures of up to 50 °C, in some cases.

Where hazardous vapours and dusts exist, the vapour or dust may be present all the time, for long periods or only occasionally. Hazardous areas should thus be divided into areas of risk of ‘release of gas, vapour or dust’.

The type and size of these hazardous areas is determined using area classification as shown in Table 1.

Table 1: Hazardous area classification.

Where hazardous gases are present, the luminaire chosen must also be suitable for operation within this gas environment. For this, luminaires are graded according to the gas group in which they can satisfactorily operate. The luminaire is certified and marked to operate in a particular gas environment as follows:

• Group I - Methane (coal mining)
• Group IIA - Propane - lowest ignition hazard
• Group IIB - Ethylene
• Group IIC - Hydrogen - highest ignition hazard

The gases above are only indicative of the gases within the groups. A more detailed gas-group listing is found in AS/NZS 60079.20 ‘Electrical apparatus for explosive gas atmospheres - Data for flammable gases and vapours, relating to the use of electrical apparatus’.

An important factor to remember is that the surface temperature of the electrical equipment must never be allowed to rise beyond the auto-ignition temperature (the temperature at which the substance will ignite automatically by itself without any external heat source) of the gas or vapour that it is put into. The T-rating - the maximum temperature that a piece of electrical equipment can reach - must be specified as being less than the ignition temperature of the hazardous material in the environment (see Table 2).

Table 2: T-ratings.

When placing equipment into service in hazardous environments, the area classification, gas groups (where relevant) and the T-rating must be known in order to prevent catastrophic failures.

Additionally, the appropriate IP rating and protection technique best suited to the application and environment must be considered. The protection techniques (Ex d, Ex e, Ex n, etc) indicate the method used to ensure protection against ignition. For example, Ex d - flame-proof equipment is robust and can stand an explosion from within and prevent the flame transmitting to the outside. Consideration of the environment into which the luminaire is to be placed is vitally important.

The luminaire selection must also be based upon the desired illumination level, colour rendering and luminous efficiency (affected by lamp and ballast combination, luminaire efficiency and luminaire distribution and mounting height). AS 1680 provides guidance on recommended lighting levels and colour rendering based upon task requirements for interior environments.

Finally, a factor often overlooked is the mounting of the luminaire, where metals of different types can come into contact resulting in galvanic corrosion. Careful attention needs to be paid to the mounting hardware and the luminaire materials so as to avoid the possibility of galvanic corrosion. This can be avoided by:

• Electrically insulating the metals from each other;
• Coating the two materials; and
• Choosing metals that have similar potentials.

The more closely matched the individual potentials, the lower the potential difference and, hence, the lower the galvanic current.

Written by Sebastian Beier, Market Sector Manager, CSE Division, Sylvania Lighting Australasia