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Home > News > FAQ - Explosion Proof Pipeline Inspection Equipment

Explosion Proof Pipeline Inspection Equipment Frequently Asked Questions

By Alan Grant

In the past several months I have received questions that are of a general nature related to sanitary sewers. I would like to provide clarification.

The National Fire Protection Association's (NFPA) standards, OSHA laws, the Instrument Society of America (ISA) standards and others will be used as they pertain to this writing.

The NFPA 820 is the recognized text for fire safety standards in the sanitary sewer arena, and the text is approved by the American National Standards Institute (ANSI). The NFPA explicitly states that they (NFPA) have no power to police or enforce compliance with the contents of the NFPA 820.

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Related link:

OSHA memo on Explosion Proof Cameras and Peripherals

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Questions:

• How is a "hazardous location" defined?
• What constitutes a hazardous location?
• Explain "authority having jurisdiction" (AHJ) and who has the authority to classify a hazardous location?
• What is the Division System?
• What is the Zone System?
• What is the difference between the Zone System and the Division System?
• What is the difference between "Explosion Proof" and "Explosion Protected"?
• What is "Listed and Labeled"?
• What is the difference in Explosion Proof and Listed and Labeled?
• If gas is detected in a sewer line, can Class 1 Division 1 equipment be used in that line?
• Does a NRTL require a manufacturer of explosion proof equipment to have a quality program in place such as ISO 9001?
• What is the future of the Division System?

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Answers:

• How is a "hazardous location" defined?
  
  

  • A location in which fire or explosion hazards may exist due to an external atmosphere of flammable gases or vapors, flammable liquids, combustible dust, or easily ignited fibers or flyings.

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• What constitutes a hazardous location?
  
  

  • The National Fire Protection Association (NFPA) provides the above explanation, and is recognized as authority on fire protection. The NFPA recognizes that even they with their vast resources cannot identify all locations and instruct in the treatment of that location. The

    NFPA relies on the "authority having jurisdiction"(definition to follow-#3) to govern what the NFPA has not addressed.

    For anything to explode or burn certain conditions have to be met. A combustible substance must be present with oxygen and an ignition source. In the case of a sanitary sewer system, a gas may be generated from the decomposition of the sewage, the chemical treatment of that sewage or the gases created from substances (gasoline, paint thinner etc.) that have entered the sewage system. These conditions may be present in lines as well as equipment housings, wet wells etc.

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• Explain "authority having jurisdiction" (AHJ) and who has the authority to classify a hazardous location?
  
  

  • AHJ Definition: The organization, office, or individual that has the responsibility and authority for approving equipment, installations, or procedures.

    This term has an extremely broad meaning. It could be a federal law that set the conditions, which determines the AHJ. In a small town sewage system it may be the town's civil engineer that sets the AHJ. It could also be the owner of a piece of property that houses a hazardous location. On that persons property he/she may be the AHJ.

    OSHA is the AHJ when it comes to employee safety. An example of that would be an electric panel in a hazardous location. The OSHA laws (example - Title 29, Code of Federal Regulations Part 1910) govern employee safety like adequate ventilation, confined space entry precautions and adequate area in which to work on an electric panel.

    Many chemical manufacturers, oil producing companies, the wood and pulp industry are their own AHJ. They best understand the situation at hand and are the best equipped to handle the hazards that may arise.

    As to who has the authority to classify the location: OSHA writes that In general the only "laws" that are universal (for the United States) are those, and they pertain to employee safety. There are several organizations that create "standards" that are used as guidelines in the hazardous location classification. OSHA in their laws "incorporate by reference" many of these standards into their writings to direct the employers as to the standard safety practices. These different guidelines are similar in nature and in most cases identical.

    The AHJ has the option of using the standards as written or may add to or omit sections as necessary. If a location is deemed as hazardous and is to be insured it is certainly best to use the standards to their full potential. The insurance companies most certainly will.

    Classifying an area as to what Division (definition to follow #4) is usually accomplished by a professional engineer that is trained in that area. Since there is such a vast difference in the locations that can be deemed as hazardous i.e., dust, gas, etc, it would be difficult to train one person for that task.

    Since sewage systems are quite similar in nature, the NFPA Standard 820 is commonly used as a guide to classify the systems.

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• What is the Division System?
  
  

  • Division 1 - A location where an explosive mixture of gas, vapor, dust fibers or flyings and air may exist under normal operating conditions.

    Division 2 - A location where an explosive mixture of gas, vapor, dust, fibers or flyings and air may exist under abnormal conditions.

    Designation of flammable substances within the Divisions is accomplished via Classes. Class I is for gas/vapor, II is dust and III is ignitable fibers and flyings.

    The concern for sewers is Class I Division 1 or Class I Division 2.

    The Division system was originated to allow us to classify hazardous locations in a uniform manner throughout the US (and the world). Those trained in classifying will use the same methodology for an oil refinery and a sewer.

    A good example of classification would be a Dry Well. This is a portion of a pumping station that is segregated from the rest of the site and is used for housing pumps, motors valveing etc. Under normal conditions this location would be classified a Class I Division 2. If at some point a valve would leak, a pump seal would fail etc., the gas that is generated by the transported waste has the opportunity to accumulate within the dry well. This would create an explosion hazard, which would be an abnormal condition.

    A Class I Division 1 example is a wet well or basin that is "not normally vented". The wet well would have the gas present under normal conditions and would be susceptible to explosion under normal conditions.

    A Sanitary Sewer and a Combined Sewer are (usually - if not ventilated) considered Class I Division 1 locations. These locations have the danger of flammable gases and floating flammable liquids. If ventilated they (usually) are classified as Division 2.

    Once again, the direction for classification exists, but the responsibility falls upon the authority having jurisdiction. The ventilated system will require a vent. The AHJ will now be required to classify the vent location.

    This vent location will be emitting flammable gasses and depending on the gases the vent location will be classified as Division 1 or Division 2.

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• What is the Zone System?
  
  

  • The Zone Classification System is the new guy on the block for the United States. It has been used in Europe for over 50 years.

    This system is no more than a method used other than the Division to classify a hazardous location.

    Zone 0 - A location where an explosive mixture of gas, vapor, dust fibers or flyings may exist under normal operating conditions for 1000 hours per year.

    Zone 1 - Same as above with the limitation of under 1000 hours per year.

    Zone 2 - Same as above with the exception of abnormal conditions.

    The Zone system has all of the same characteristics as the Division as in classes of gases, dusts etc.

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• What is the difference between the Zone System and the Division System?
  
  

  • Without going into lengthy detail, the short definition would be, the methodology employed in the design of an entire electronic or electrical system.

    The Division System uses a methodology called "explosion proof" where the Zones System uses "explosion protected".

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• What is the difference between "Explosion Proof" and "Explosion Protected"?
  
  

  • Once again, without going into lengthy detail, the explosion proof way of thinking is to contain the explosion in a very heavy cast aluminum or cast iron enclosure. This allows the gas to get in, explode and leak out at a slow enough rate that the gas has cooled enough so as not to ignite the surrounding atmosphere. Conduit that is used must be sealed so that gas may not move from one enclosure to another.

    The explosion protected system eliminates the ignition point from which an explosion may be generated. Components used for this system are laboratory tested and approved for use in the Zone locations. Mineral insulated cables may be used in lieu of conduit and cable grips are used instead of sealed conduit piping.

    For either system, a combustible material, air and an ignition point are required for an explosion. The Zone system removes the ignition point.

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• What is "Listed and Labeled"?
  
  

  • In the United States we have a system of testing hazardous location components. When an item is tested and has proven to be safe, it is then "listed and labeled" as such. The components range from terminal blocks for electrical connections to very sophisticated camera systems for pipeline use. This pipeline may be an oil transportation system or a city sewer.

    The testing for the "listing and labeling" is accomplished by a "Nationally Recognized Testing Laboratory" (NRTL) of which we have fourteen at present. Underwriters Laboratories and Factory Mutual are the best known.

    The NRTL's will test to specific requirements set forth by knowledgeable bodies and will test to their own criteria. They will test to the component level and will also test complete systems. When testing complete systems all components in that system must meet the requirements for the location for which it is being tested.

    As an example. If a video system for a pipe line is being tested for use in a sewer, that system would have temperature limits for the motors that drive the tracks. The lighting system must have a temperature limit set. The moving parts that are exposed to the pipes inner atmosphere must be incapable of creating a spark. Cable connections must be such that they meet specifications related to "pull out" so as not to create an "arc or spark". When all of the criteria is met for the hazardous location, the "system" is listed with whatever agency has tested it and then can be labeled as safe for a hazardous location.

    As to weather an AHJ will accept that list and labeled criteria is up to AHJ.

    This brings up another matter. Does a piece of equipment have to be "listed and labeled" to be safe in a hazardous location? No. A piece of equipment may be designed, built and be perfectly safe for a hazardous location and never be tested by an NRTL. The AHJ will have the jurisdiction to approve that piece of equipment before use.

    This works in the other direction as well. If a piece of equipment is listed and labeled by an NRTL, the AHJ may say that they (the AHJ) do not approve it and it may not be used.

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• What is the difference in Explosion Proof and Listed and Labeled?
  
  

  • The term listed and labeled can pertain to nearly anything that is inspected by a NRTL. This can be the toaster on your kitchen counter or a sophisticated computer control system at your workplace.

    The term explosion proof pertains to the Division System of classifying a hazardous location.

    The term explosion proof usually is thought of in conjunction with the heavy cast aluminum or cast iron enclosures that are used in the Division system.

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• If gas is detected in a sewer line, can Class 1 Division 1 equipment be used in that line?
  
  

  • The reason for our approvals system is that when a piece of equipment is approved, it may be used for it's designated purpose.

    This is not to say that good common sense should not be used - explosion proof is not fool proof.

    If gas is found in a line and there is a manner in which the gas can be removed or diluted to a safe limit, then by all means it should be done before any type of equipment is used.

    The gas in a sewer line is usually classified as methane. Methane under the Division system is a Class 1 gas that has an ignition point set at 450° . The actual ignition point is about 560° but for safety's sake the safe temperature is set at 450° .

    In this case, the lights that are affixed to the camera cannot be allowed to reach the 450° mark.

    The motors that drive the carriage cannot be permitted to reach the 450° mark, etc. And yes the carriage itself may not cause a spark that reaches the 450° mark and set off the gas.

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• Does a NRTL require a manufacturer of explosion proof equipment to have a quality program in place such as ISO 9001?
  
  

  • No.

    NRTL's cannot mandate how a manufacturer operates their business. However ISO 9001 does reflect the thinking of a manufacturer.

    A manufacturer that goes through the extensive amount of work that is synonymous with ISO recognition obviously cares about the quality of their product.

    The ISO recognition would not have a bearing on the NRTL approval system but should reflect a higher image for those doing comparisons before purchase of like items.

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• What is the future of the Division System?
  
  

  • Although no one can tell the future, I will go out on a limb and say that the Division System will now be short lived. The Zone System is a much more highly developed system than that of the Division. Zones are used by the world in it's entirety and now finally is working it's way into the US. The Zone methodology allows the use of the Division way of thinking as well as that of the Zones. It does not (Repeat-does not) eliminate the Division rules. The two can work together. At present the National Electric Code segregates the two systems. My assumption would be that it is meant to lessen the confusion as the Zone System works it's way into our country.

    In the new NFPA 820 as well as in the other NFPA standards that I have read, the introduction states (paraphrased) that if there is an alternate method or equipment that is equivalent to or better, that it may be used. This in itself allows for the use of the Zone system.

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