Lighting fixtures for hazardous areas: selection guide
The sight is one of the main negative health effects related to work in unsuitable lighting conditions. The glare caused by excessive environmental lighting and the physical and mental effort used to work in low light conditions are the most frequent causes.
Therefore, unsuitable lighting often leads to wrong behaviors: this means that the choice of the right lighting is very important, this is even more relevant in hazardous areas where the need to have an adequate lighting for working in compliance with the safety standards must be combined with the capacity of the appliance to contain an explosion.
The characteristics of a lighting fixture are essentially three:
• Containment: the lighting equipment is a protected case that contains and protects lamps, lampholders, power switches, terminals.
• Electrical safety: the lighting equipment must be compliant with EN standards with adequate protection degree.
• Lighting engineering functions: relate to the luminous flux emitted by the lamps. It is important to have a lighting engineering calculation made specifically for the area to be illuminated.
For the creation of a lighting project it is necessary to keep in mind the following concepts:
• reflection (When
a wave hits a smooth object that is larger than the wave itself, depending on
the media, the wave may bounce in another direction);
• Scattering (occurs when a signals wavelength is larger than pieces of a medium the signal is reflecting from or passing through due to the collision with other particles). The scattering occurs random and for this reason it is different from reflection and refraction which change in a regular and determined way;
• refraction (the deviation of a wave when it passes from one medium to another, its propagation speed changes).
In designing a lighting system, it must also be kept in mind that the efficiency of the lighting fixtures lapses over the time due to aging and the deposit of dust on the reflectors and on the diffusers.
In the lighting calculation, it is then necessary to indicate the type of lamp. For explosion proof lighting fixtures this means:
- the type of lighting (LED or not)
- the protection mode (Ex d, Ex e, Ex n).
- Ex d – Flameproof: The main feature is a strong and robust construction, which guarantees a high reliability for a long time. Usually made of aluminum alloy and borosilicate glass, the Ex d lighting fixtures are used in places where, in addition to explosion protection, a good mechanical protection of the equipment is required.
- Ex e – increased safety: The main feature is that the equipment with this protection method is designed to prevent sparks even in irregular operating conditions. The Ex e lighting fixtures are usually constructed with plastic resins, such as polyesters and polycarbonates, which make them light and easy to install and maintain, as well as allowing simple replacement of the lamps. Furthermore, plastic resin is preferred for use in situations of corrosion in the presence of salt fog and in environments with an aggressive atmosphere due to the presence of strong inorganic acids. On the other hand, however, the polycarbonate used can lose its transparency characteristics over time, tending to turn yellow. In comparison, aluminum and glass have better performance against aging as the glass guarantees maximum transparency over the years.
- Ex n – Simplified: the main feature of this type of protection is the considerably lower cost compared to other protection modes, this is due to the fact that the Ex n lighting fixtures are suitable for zone 2/22 only.
The equipment is divided into “non-sparking” and “sparkling” equipment that can produce sparks, arcs and cause high surface temperatures during normal operation. Based on this classification, it will therefore be possible to have the Ex nA method for non-sparking equipment, Ex nC method for sparking equipment, and Ex nR method for rrestricted breathing enclosures.