Lighting of places with risk of explosion

INTRODUCTION The correct lighting of work places is a growing concern in order to guarantee the safety of people who works on plants. In...

INTRODUCTION

The correct lighting of work places is a growing concern in order to guarantee the safety of people who works on plants. In particular, in electrical plants installed in hazardous area, lighting features are considered as a means to reduce risks of explosion. About 80% of our sensorial perception is visual and needs light as a vehicle of information, to interpret information from visible light reaching the eyes. A good illumination helps to see and recognize things, but also improves working performances and physical wellness, since it increases concentration and reduces tiredness. Equipment installed in classified zones, hence, have to guarantee the ex-proof protection and a good light stream in order to guarantee work operations in safety conditions.

LIGHTING EQUIPMENT

A lighting fixture is a unit consisting of: a light source or lamp, a power supply, devices for igniting and supplying power, optical elements directing the luminous flux and all the mechanical parts necessary for containment, wiring and installation. Three are the main functions of a lighting fixture:

  • Containment and support: a housing contains lamp, lamp-holder, power supply and terminals, to protect them against environmental stress;
  • Electrical safety: electrical safety must comply with the requirements of EN60598 60598-1:2008 e EN 60598-2 standards, concerning protection level, protection against direct and indirect contacts, against short circuits and earth failures. According to the Italian law No. 81/2008 the employer is responsible to guarantee the safety in work places;
  • Lighting or photometric functions: regard the development of the flux emitted by the lamp.

The basic functions to consider in lighting design are:

  • reflection (the flux is concentrated in a cone characterized by a defined beam angle),
  • diffusion (a beam of light is divided into a series of diverging rays),
  • refraction (the incident ray is deflected from a lens or a transparent prismatic body at a certain angle).

When projecting a lighting system, it is not only important to consider the visual comfort; it is also very important to consider that lighting devices loose efficiency with passing of time (lamp flux decreases and dust deposits on reflectors and diffusers). The data of aged lighting fixtures shall therefore be considered, during the project stage, in order to foresee the flux deterioration in percentage after installation.

Protection methods applicable to lighting fixtures

Equipment for hazardous areas must be designed, assembled and certified according with ATEX 94/9/CE standard.

Following are described the main protection methods applicable to lighting fixtures:

  • Ex “d” explosion-proof: This method is based on the concept that it is impossible to prevent a gas from spreading. The main advantage of this protection method is that the lighting fixture, which is built to contain explosions, houses common electrical components which are easy to find on the market.
  • Ex “e” increased safety: This protection method applies certain measures to prevent the formation of arcs, sparks. The main advantage of this protection method is the simplicity of use and construction. The lighting fixtures require special components, which must be individually protected according to one of the standardized methods. These components are quite difficult to find on the market and must be supplied by the manufacturer at high costs.
  • Ex n” simplified: This protection method involves using other protection methods in a simplified way. It makes on electrical equipment unable to cause the ignition of an explosive atmosphere even during normal operation. Its main advantage is again simplicity of use and construction. Once again, the equipment needs specific components, which are specifically produced for the each type of fixture. Furthermore, its use is only for Zone 2.

CONCLUSIONS

We can therefore conclude that there is no universal or perfect protection method. The important thing to remember is that all the methods are effective provided that they are applied correctly following their construction criteria, and that the equipment is kept in its original condition of safety by careful maintenance.

Fecha de publicación: 01-06-2010

Tema: Additional information