Protection from flammable compounds in industrial facilities vary greatly. Some standards rely on the use of non-sparking materials and sealed housings (explosion proof), while other practices focus on low-energy designs to reduce ignitions (intrinsically safe). Understanding the role that such preventive measures play is crucial to promoting safety in dangerous work environments.
This article compares the difference between intrinsically safe and hazardous areas.
Hazardous Areas
The term ‘hazardous areas’ refers to a location where flammable substances (liquids, dust and/or vapors) may exist during normal working conditions or stand the potential to or periodically exist at the site. It is a description used to classify specific working environments, so that safety standards can be applied, based on the characteristics of the area. Explosion proof or hazardous location guidelines are applicable to preventing combustions in hazardous areas.
Article 500 in the NEC provides the following information about explosive classifications for hazardous areas:
- *Class I, Division 1 & 2: Flammable gases/vapors
- *Class II, Division 1 & 2: Combustible dust
- Class III: Volatile fibers
Each classification above can be broken down further into several groups. Such designations are used to specify the type of elements that fall within the scope of the standard. For instance, Group B is used to describe equipment for hazardous areas that address hydrogen. On the other hand, Group G is applicable to environments that deal with combustible grain dust.
Defining Intrinsically Safe
Intrinsically safe is a set of design standards that are applicable to explosive environments, including hazardous areas. Generally speaking, this requires the use of low voltage (at a range lower than 29V DC and below 300 mA). When it comes to operating temperatures, a T4 rating is appropriate for meeting intrinsically safe standards, as this temperature classification’s threshold is 135°C.
As mentioned earlier, the main objective of intrinsically safe designs is preventing ignitions and unwanted arcing, which can lead to interactions with volatile substances. This is achieved through equipment designs that utilize low currents (electrical) and controlled operating/surface temperatures (thermal). In the event of fault conditions or equipment failure, intrinsically safe features prevent fires.
An intrinsically safe design may incorporate an intrinsically barrier, which effectively reduces the amount of power passing through the explosive site. Such measures prevent the possibility of unforeseen electrical surges damaging circuits and generating combustions.
Compared to explosion proof/hazardous location designs, wherein ignitions are contained within the unit, so that sparks cannot interact with combustible materials in the area, intrinsically safe proactively ensures ignitions are not created. Therefore, there is no need to include features that contain such elements (conduit and seals are not needed).
Additionally, taking into consideration that explosions are generated by fuel, oxygen and a heat source, intrinsically safe standards remove the final element from the equation (heat source or ignition). By comparison, explosion proof/hazardous location practices aim to reduce fuel and oxygen.
Benefits and Advantages
Hazardous Areas:
- Uses explosion proof/hazardous location standards to address ignitions
- Helps operators understand the volatile characteristics of the work site
- Helps manufacturers design equipment for use in combustible facilities
- Safety standards (explosion proof) cater to high-power/high-energy equipment
- Can be costly to implement (explosion proof equipment)
- Explosion proof devices tend to be bulkier and heavy due to protective measures and rugged materials
Intrinsically Safe:
- Low-cost to implement, compared to explosion proof equipment
- Maintenance and repair is less time consuming (in most cases, no shut down required)
- Active ventilation is not needed
- Can be limited to low-power devices
- Effective during fault conditions or equipment failure
- Addresses entire system – not based on components