Ensuring Hazards Are Covered
For all intents and purposes, the somewhat professional life of a significant number of fire professionals is rarely disturbed by the need to protect areas classified as hazardous. And when the need does arise, there are only two choices: fill the client’s need or walk away from the job. Areas classified as hazardous are commonly found in chemical plants, paint spray booths and others.
Hazardous areas are defined in Section 3-2, NFPA 101, 1997 Edition as: “Those areas of structures or buildings posing a degree of hazard greater than that normal to the general occupancy of a building or structure, such as those areas used for the storage or use of combustibles or flammables, toxic, noxious, or corrosive materials; or heat-producing appliances.”
There are many places fire technicians can turn to for advice when protecting classified areas, such as System Sensor of St. Charles, Ill., and the National Fire Protection Association (NFPA).
System Sensor offers an excellent white paper that details the process of protecting hazardous areas. “Intrinsically Safe Fire Protection Devices” discusses the various standards as well as how to use them. NFPA publishes standards on hazardous area protection, such as the National Electrical Code (NEC) and Life Safety Code.
This month, we’ll cover the basics concerning hazardous area protection. Next month, we’ll cover the selection and installation of notification appliances and initiating devices designed for classified areas.
Why We Fuss Over Classifications
Most of the applications fire alarm technicians deal with are not classified. But every now and again a job comes along where the atmosphere is conducive to explosion and/or fire. Selecting components for these jobs is usually straightforward and simple, but the subject requires study and a good knowledge of the various code sets.
When a facility contains a classified area, it’s the fire alarm professional’s job to protect the occupants from the risk of fire and explosion. To make matters worse, unless the notification and initiating devices used are specially designed to contain either condition, the fire alarm devices could cause a catastrophic reaction. Therefore, all the initiating and notification devices installed in these areas must be sealed, ruggedized and listed by a third-party testing lab, such as FM Global or UL.
For example, listed notification appliances must be built so an internal explosion or fire cannot cause the same or a similar reaction in the vicinity of the device. This is especially critical where the surrounding atmosphere is volatile in some manner. The cost for these specially designed and listed components is many times more than their nonhazardous, conventional counterparts.
It doesn’t end with the devices either, for the cable that connects the devices to a fire alarm panel or power supply must also be installed in sealed, rigid conduit. Wire connections must also be placed in sealed junction boxes designed and rated for the hazard. It’s important to know when and where to use these devices to avoid problems.
A simple misunderstanding concerning the rating of a particular classified area can mean the difference between a profitable job and one that can cost the fire alarm company thousands of dollars. This is why it pays to understand the business of hazardous area protection.
NEC Authorizes Area Classification
In order to properly protect such hazardous areas, fire professionals must understand how fire- and explosion-prone areas are classified. Without this knowledge it’s next to impossible to properly plan and execute a specification. Such an assessment must begin with a thorough understanding of the hazard itself.
Note Article 500.5[A], NFPA 70, NEC, 2002 Edition, published by NFPA: “Locations shall be classified depending on the properties of the flammable vapors, liquids, or gases, or combustible dusts or fibers that may be present, and the likelihood that a flammable or combustible concentration or quantity is present. Where pyrophoric materials are the only materials used or handled, these locations shall not be classified. Each room, section, or area shall be considered individually in determining its classification.” According to the comment section contained in Article 500.5(A), NEC Handbook, 2002, “Pyrophoric materials ignite spontaneously upon contact with air. The use of electrical equipment that is suitable for a hazardous (classified) location will not prevent ignition of pyrophoric materials. The process containment system should be designed to prevent contact between pyrophoric material and air.”
Hazardous Area Terminology
There are several basic standards that dictate which devices to use and where to use them. These classifications involve class and division, as well as group and zone. In the United States, all are commonly used except zone.
To better understand the meaning of class and division, we turn to Articles 500 through 504 contained in NEC, also designated as NFPA 70, 2002 Edition.
“Articles 500 through 504 cover the requirements for electrical and electronic equipment and wiring for all voltages in Class I, Division 1 and 2; Class II, Division I and 2; and Class III, Division I and 2 locations where fire or explosion hazards may exist due to flammable gases or vapors, flammable liquids, combustible gases, or ignitable fibers or flyings.”
The short description of Class I, II and III is as follows:
- Class I hazards involve gases and vapors
- Class II hazards involve combustible dust
- Class III hazards involve combustible fibers or flyings
Putting It All Together Class
and division designations go together in such a manner that authorities, as well as fire protection professionals, know what kind of risk exists in any given special areas. Not only does this help fire alarm professionals better understand how to protect classified areas, but it also tells firefighters and their commanders what to expect when an incident occurs.
For example, a location falls under Class I, Division 1 when flammable gases or vapors exist in sufficient quantities that an explosion or fire can occur during normal conditions. The same classification includes the risk of explosion or fire due to routine maintenance.
The same classification also applies to situations where a sufficient concentration of gas or vapor exists for ignition because of a breakdown or the incorrect operation of equipment. This includes the failure of electrical apparatus, resulting in a condition suitable for ignition.
Class 1, Division 2 involves applications where flammable liquids or flammable gases could escape during the course of storage, handling or production. These gases and liquids, which are commonly kept in containers, might escape due to accidents and other similar situations.
NEC also cites situations where gases and the vapor from volatile liquids may be present during normal conditions, but the concentrations are kept to a minimum due to ventilation. In this instance when one or more ventilation units fail, gas and vapor concentrations could reach the point of ignition.
The same principles of application also apply to Class II, Division 1; Class II, Division 2; as well as Class III, Division 1 and Class III, Division 2. Instead of gases and liquids/vapors, however, Class II deals with combustible dust and Class III deals with ignitable fibers and flying embers. See next month’s “Fire Side Chat” fo
r a continuation of this topic.
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