Questions and Answers
Fires or explosions may occur when basic conditions exist?
3
Which of the following materials would be found in one of the three location classes of class division system?
The possibility that a gas mixture may be above the upper flammable limit does not ensure that gas is safe. The gas must first pass through flammable range as its ___ increases from being below the lower flammable limit to a concentration above the upper flammable limit.
concentration
A source of ignition is all that is needed to create a fire or an explosion where ignitable or explosive mixtures are present.
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Equipment with contacts, such as switches and circuit breakers, can produce arc sparks during normal operation when?
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Materials in class one division one and division two hazardous classification locations are assigned to one of four groups. What are these groups?
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A class one division two location is one in which flammable gases, flammable liquid produced vapors or combustible liquid produced vapors are?
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An alternative classification system was added to the NEC in 1996. What is the article number?
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Metal combustible fibers/flying are classified as?
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The upper flammable limit of the highest molar concentration of a combustible substance in an oxidizing medium that will propagate a flame is referred to as?
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An area where nonmetal combustible fibers/flyers are in the air is classified as class three division one.
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Protection technique concepts include?
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A class two liquid has a flashpoint at or above 100°F but below 140°F. What is the flashpoint?
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Article 505 of the NEC has ___ revisions in the 2023 edition.
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The flashpoint of a liquid is the minimum temperature at which it gives off a vapor, sufficient concentration to form an ignitable mixture with air. What is this rate known as?
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Explosion-proof equipment must withstand a hydrostatic pressure test in a range of ___ times the maximum pressure.
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The purged and pressurized protection technique is permitted in any hazardous classified location for which it is identified. What is the article number?
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Combustible liquids will only form an ignitable mixture when they are heated above their flashpoint.
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When explosions run through a conduit system, the gas in front creates a pressure piling effect that may result in extreme explosive and mechanical pressures. What does this describe?
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Which of the following methods are used to make plug receptacle combinations safe for use in hazardous classified locations?
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The 1975 revision of the NEC added the word 'classified' to hazardous classified locations.
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The use of ___ in hazardous locations is prohibited by special bonding requirements.
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A zone zero location is a location in which ignitable concentrations of flammable gases or vapors are present. What is the article number?
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The first mention of hazardous locations appeared in the 1920 edition of the NEC.
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Article 506, which covers zone rate system requirements for class/division hazards, was added to the NEC in 2005.
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In the 1959 NEC revision, the requirements for hazardous locations were formatted into four articles: 500, 501, 502, and 503.
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Article 510, created in 1953, for six special occupancies was finally deleted in 2023.
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The point where a flammable or combustible substance is capable of ignition depends on the substance types and which of the following?
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Refrigerant machinery rooms containing ammonia are permitted to be classified as classified locations if they have adequate mechanical ventilation that operates continuously or a detection system initiates the ventilation when ammonia concentration reaches what level?
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Special bonding requirements can be found in which article?
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Bonding requirements can be found in which article?
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Explosion-proof or tastic nation proof equipment is not permitted for use at temperatures lower than -13°F unless identified for low temperature service.
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Study Notes
Hazardous Classified Locations
- Fires or explosions can occur when basic conditions are met.
- Materials in hazardous categories are classified based on the potential for fire or explosion risk.
- Flammable gas concentrations must pass through the flammable range to reach explosive levels.
Ignition Sources
- A source of ignition can trigger a fire or explosion in the presence of flammable gas mixtures or combustible dust.
- Equipment such as switches and circuit breakers can produce sparks during normal operation, posing ignition risks.
Classification Systems
- Class 1 Division 1 and Division 2 locations are defined by the presence of flammable gases or vapors.
- A class 2 liquid has a flashpoint between 100°F and 140°F.
- Article 505 of the NEC, introduced in 1996, outlines alternative classification systems.
Explosion-Proof Equipment
- Explosion-proof equipment is designed to withstand explosions caused by specific gases or vapors.
- Hydrostatic pressure tests for explosion-proof equipment range from 3 to 6.5 times the maximum pressure it may encounter.
Flammable Concentrations
- Combustible liquids require heating above their flashpoint to form ignitable mixtures.
- Different classes of hazardous locations (e.g., Class 3 Division 1) have specific definitions related to the presence of nonmetal combustible fibers or flying particles.
Regulatory Changes
- Article revisions over the years have adjusted definitions and classifications of hazardous locations.
- The NEC's 1975 revision added the term "classified" to hazardous locations, emphasizing safety standards.
- Significant updates were made in the NEC's 2023 edition and previous years, including the deletion of certain articles.
Special Conditions
- Refrigeration machinery rooms with ammonia systems can be classified as hazardous if proper ventilation is maintained.
- Special bonding requirements exist for hazardous locations to ensure safety against potential ignition sources.
Historical Context
- The first mention of hazardous locations in the NEC was in the 1920 edition.
- Requirements for hazardous locations were formally structured into articles in the 1959 NEC revision.
Miscellaneous
- The upper flammable limit represents the highest concentration of a combustible substance that can sustain a flame.
- Pressure piling can occur during explosions in conduit systems, leading to extreme mechanical pressures.
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Description
This quiz covers essential concepts related to hazardous classified locations, ignition sources, and explosion-proof equipment. Understand the classifications of materials based on fire risk and the impact of ignition sources in flammable environments. Test your knowledge about safety measures and regulatory standards in hazardous areas.
