Why are Explosion Proof Lights Different?|
Marine engine rooms, commercial paint booths, chemical storerooms, grain silos, tank farms; what do they all have in common? Each and every one of these is a potential bomb waiting to go off. Under certain conditions and with the right combination of circumstances, the possibility of a catastrophic explosion occurring becomes a near certainty. When the conditions are right in any of these settings, the only thing keeping the unthinkable from happening is the lack of an ignition source. In an atmosphere that has become contaminated with volatile gases, or heavily saturated with combustible dust, all it takes is one tiny spark to set in motion a chain of reactions that can lead to fires, explosions, and injuries.
In many of these settings, it is in fact common for a flammable atmosphere to be present, and there is no practical way to completely avoid producing these conditions. Because these conditions are often created as a part of the normal operations of industry and cannot be totally negated, the next obvious solution is to remove all possible sources of ignition. Doing this is easier said than done, since in industry there are so many sources that must be considered. Everything from light switches to fans are possible sources of ignition, and they simply cannot be entirely removed the workspace. It’s because of this that specialized versions of equipment that must be operated in these hazardous environments have been developed and are mandated for use in hazardous locations by OSHA.
Equipment for use in hazardous locations has several ratings and categories that indicate the suitability of the equipment for use depending upon the level of danger a particular location may create. For the control of ignition sources, most regulations deal in mandating either intrinsically safe electrical equipment, or explosion proof equipment. The differences between the two are subtle, but important. Intrinsically safe equipment is basically any equipment that is incapable of producing sufficient energy to cause ignition. Explosion proof refers to equipment that can contain and isolate possible sources of ignition, preventing them from making contact with the open air. It would seem obvious that intrinsically safe would be the highest safety rating, and in fact it is. Intrinsically safe rated equipment is suitable for use in all the hazardous location groups and ratings as defined by OSHA regulations. Despite this, intrinsically safe equipment is not always the best choice because of the limitations created by its higher costs and generally low power characteristics.
Explosion proof equipment on the other hand is not as constrained by the limitations imposed by the intrinsically safe rating, and allows for a broader and more powerful spectrum of equipment to be used, and at cheaper cost. Since the explosion proof rating only requires that sources of ignition be contained, and temperatures be kept below certain levels for varying division ratings, the basic design of equipment can remain intact, with additional design incorporated to contain its normally open sources of possible ignition. A basic example would be a simple light switch. In normal conditions, a light switch has at its core a contact point where two metal conductors are put into contact with each other to form a closed circuit, thereby transferring electrical energy to the lamp.
It is at this contact point that a possible ignition source is created as the two conductors come into contact with each other and produce a small spark or arc. Isolating this spark can be as simple as encasing the entire switch within a sealed and non conductive exterior such as rubber, thereby removing the conductive portion of the switch from contact with the outside atmosphere. This is a greatly simplified example, but it demonstrates the basic premise. To better understand the full premise behind making electrical equipment explosion proof, and just how much is involved in the design, it is better to look at something a bit more complicated.
For a better idea of just how much goes into producing explosion proof rated equipment, let’s look at the Larson Electronics Explosion Proof LED Drop Light: Part # EHL-LED-7W.
One of the first things you’ll note is how different this drop light’s appearance is from ordinary drop lights. While the overall shape and design appearance is the same, it is somewhat stouter and much more rugged looking. This is due to the necessity of incorporating a stronger basic body assembly. As well as sealing possible sources of ignition from contact with flammable dust or vapors, the assembly must be able to contain any ignition of gases within its housing; if a bulb were to explode, or gases to get inside and ignite, the housing is capable of containing these long enough for them to cool below ignition temperatures before they can escape. In a traditional drop light, there is no sealing, and the assembly is a great deal less rugged.
The next thing you would notice is that the lamp is constructed of non sparking materials. The body is made from high strength composites, the metal cage and lamp housing is aluminum, and the cord is chemical and abrasion resistant. This allows the lamp to be accidentally dropped, and greatly reduces the chances that an errant spark is created when it contacts the ground. Further enhancing the safety of the lamp is a clear impact resistant enclosure that seals the bulb itself from the outside environment. The bulb and the enclosure are both protected from impacts by a strong aluminum cage, reducing the chances of damages from impacts. Traditional drop lights have little to no concern for the metals used in construction aside from production cost, and rely on thin steel and tin for most of their metallic components.
In this particular lamp, LEDs are used instead of a typical incandescent or fluorescent bulb. These LEDs create less heat than traditional bulbs, and produce a greater amount of light with less power. As well as being more efficient, the LEDs are also a great deal more resistant to damage from dropping or impacts. Traditional bulbs rely on a fragile tungsten filament to produce light through resistance to electrical current. This fragile filament is easily broken by vibration or impacts. As well as being easily damaged, a traditional bulb relies on a gas filled enclosure surrounding the filament to increase the life of the filament. This glass enclosure is also easily broken, and represents an ignition hazard if it breaks during use and exposes the hot filament to an explosive atmosphere. With the LED bulb, there is no gas filled enclosure to break, and no heated filament to present an ignition source. This has the effect of further improving this lamps resistance to creating an errant ignition source.
Lastly, you’ll note that all the parts of this assembly are tightly and securely sealed together. Unlike traditional lamps, all the seams and connections are sealed with gaskets and fillers that isolate the internal electronics of the unit from the outside. Contaminants are kept out, and possible ignitions are kept in, removing the possibility of a chance ignition of the volatile compounds that may be present.
As well as being ruggedly designed and explosion proof, this lamp is also very energy efficient. The LED bulb uses a fraction of the power a normal bulb consumes. At only 7 watts, this LED lamp produces the light equivalent of a standard 100 watt incandescent. The life of the LED is significantly longer as well, with the LED bulb rated at approximately 50,000 hours of life, while a traditional incandescent is typically rated well below 5000 hours. This means less trouble and expense with replacing the bulb. As well as consuming less energy, the LED bulb produces far less heat. In a standard drop light, none of the above features are present. It is commonly understood that frequent bulb replacements and occasional burns from contact with the hot housing assembly are a part of using the standard incandescent lamp. Not so with LEDs.
As you can see, there is a great deal of consideration and design that goes into creating a high quality piece of explosion proof equipment. Although the basic premise is still to produce a simple and efficient source of illumination, the added requirements of an explosion proof rating increases the demands for durability and ruggedness. In these lamps provided by Larson Electronics, those requirements are met and exceeded.