Explosion Proof and Intrinsically Safe Lighting in Confined Spaces|
Article-January 2013 By Larson Electronics.com
Larson Electronics Explosion Proof Compact Fluorescent Drop Light
Confined spaces represent some of the most hazardous areas a worker can access. Because of the potential for becoming trapped, the possible presence of pooled gases and vapors, and the likely presence of unshielded machinery and equipment, the chances for accidents are high and the speed with which they can occur is great. Workers must take extraordinary precautions before entering a confined space, even in situations where rescue efforts or critical repairs necessitate fast response.
Confined spaces in many cases are required to be marked as such and require that only permit holding personnel be allowed to enter. Even in areas not clearly marked as permit required, if the potential exists for trapped toxic or flammable gases or vapors to be present, or access is limited, or the space holds materials which could engulf a worker, or if the space is otherwise not intended for a workers physical presence, they should be considered a hazardous confined space.
Even a simple container or pipe can appear harmless yet pose a serious threat to safety should ingress become required. Just because the space looks empty or there are no obvious threats from exposed wiring, equipment or gear, does not mean entrance can be considered safe. Confined spaces due to their very nature tend to trap gases and vapors which can either pose an inhalation risk or potential for ignition, or the area can lack adequate oxygen and produce potential asphyxiation. In either of these cases, the very atmosphere itself poses and invisible threat that can be just as lethal as a visible one.
The biggest part of safely entering and working within a confined space involves proper preparation. A detailed threat assessment before entrance, a clear exit strategy, and properly chosen gear are a must before any entry can be performed. Particularly in cases where a space could potentially contain a hazardous atmosphere, testing for oxygen levels and the presence of dangerous gases is critical to being able to properly prepare for entrance. In cases where a breathable atmosphere is not present or toxic vapors are present, workers will be required to carry their own air. In cases where flammable or explosive gases and vapors are present, any electrical equipment to be used inside the confined space must be appropriately designed to work within such environments.
Of all the equipment typically used within confined spaces, lighting is the most common. There are normally no integral light sources within confined spaces, and the limited access and sealed nature of most confined spaces greatly limits the amount of ambient light which can enter, thus workers must provide their own illumination. There are only two types of lighting which should be considered suitable for use within confined spaces, either equipment that is approved explosion proof, or certified intrinsically safe. Additionally, this lighting gear must be chosen according to the type of atmosphere present as not all gases and vapors present the same fire or explosion potential. As a result, explosion proof equipment must be chosen according to Class, Division and Group ratings in order to ensure compliance with regulations and suitability for use around a particular set of gases or vapors. Intrinsically safe equipment is typically the highest safety rating and denotes equipment which is incapable of producing the heat or sparks required to cause ignition, thus it is suitable for the widest array of environments. However, intrinsically safe lighting is typically lower powered and limited in its ability to illuminate an area effectively, thus oftentimes limiting its practicality.
If flammable or explosive gases or vapors are found to be present within the confined space, explosion proof lighting must carry a Class 1 Division 1 rating. Equipment rated as Class 1 means it is rated for use with gases and vapors. Class 2 denotes combustible dusts and therefore would not be suitable in an environment contaminated by gases. Of course, if dusts are present, then obviously Class 2 equipment would be the correct choice. Division 1 denotes the active and continuous presence of these flammable or explosive materials. Since if an atmospheric test revealed their presence, then a Division 1 classification is correct. Division 2 refers to the presence of flammable or explosive gases or vapors under abnormal conditions, meaning a possible leak or otherwise unexpected presence of these materials, and thus does not hold the proper protections.
The more subtle yet equally important next consideration is what Groups the device is approved for. Groups denote the types of gases present and are categorized according to their ignition temperature and explosive potential. Since not all gases or vapors will ignite at the same temperatures or burn with the same rapidity or release of energy, this is obviously an important classification.
Groups encompass a wide variety of materials, but a general breakdown is as follows. For a more complete list, operators should refer to the NFPA’s National Electrical Code publication.
Group A refers only to Acetylene which has an extremely high explosion pressure.
Group B refers to Hydrogen, gases with more than 30% hydrogen by volume, butadiene, and other gases with similar explosive properties.
Group C refers to ether, ethyl, and ethylene gases, and other gases of a similar potential.
Group D refers to gasoline, acetone, ammonia, benzene, butane, methanol, propane and other more commonly encountered compounds.
As we can see, even with the proper Classification and Division, unless groups are also considered, safety as well as compliance with regulations is not ensured.
It is also worth noting that a most lighting equipment relies on power supplied from external sources, meaning it has a cord which must be connected to a power source. In most cases, the connection must be either be made outside of the hazardous location, or a plug and receptacle which also carries the same approvals as the fixture itself must be used. Some equipment relies on a transformer or ballast assembly somewhere inline with the power cord; in these cases the transformer or ballast assembly usually must also remain outside of the confined space.
Confined space safety is a multi-faceted issue that requires comprehensive assessment in order to be addressed effectively. Worker preparation, site testing, equipment selection, and exit strategies all play critical roles and must be diligently addressed if entry is to be performed safely.