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Questions and Answers
Fires or explosions may only occur when basic condition(s) exist(s). How many basic conditions are there?
Fires or explosions may only occur when basic condition(s) exist(s). How many basic conditions are there?
3
Which of the following materials would be found in one of the three location classes of the class/division system?
Which of the following materials would be found in one of the three location classes of the class/division system?
- Material 1
- Material 2
- Material 3
- All of the above (correct)
The possibility that a gas mixture may be above the upper flammable limit does not ensure that the gas is safe. What must the gas first pass through?
The possibility that a gas mixture may be above the upper flammable limit does not ensure that the gas is safe. What must the gas first pass through?
concentration
A source of ignition is all that is needed to create a fire or an explosion when a flammable mixture is present.
A source of ignition is all that is needed to create a fire or an explosion when a flammable mixture is present.
What type of equipment can produce arcs or sparks in normal operation and become a potential ignition source?
What type of equipment can produce arcs or sparks in normal operation and become a potential ignition source?
Materials in Class I, Division 1 and Division 2 hazardous locations are assigned to how many groups?
Materials in Class I, Division 1 and Division 2 hazardous locations are assigned to how many groups?
A Class I, Division 2 location is one in which flammable gases, flammable liquid-produced vapors, or combustible liquid-produced vapors can be found. What are the levels of such materials?
A Class I, Division 2 location is one in which flammable gases, flammable liquid-produced vapors, or combustible liquid-produced vapors can be found. What are the levels of such materials?
An alternate 'zone classification' system found in Article ___ was added to the NEC in 1996.
An alternate 'zone classification' system found in Article ___ was added to the NEC in 1996.
Metal combustible fibers/flyings are classified as what?
Metal combustible fibers/flyings are classified as what?
The upper flammable limit is the highest ___ concentration of a combustible substance in an oxidizing medium that will propagate a flame.
The upper flammable limit is the highest ___ concentration of a combustible substance in an oxidizing medium that will propagate a flame.
An area where nonmetal combustible fibers/flyings are in the air under normal operating conditions in quantities sufficient to produce explosible mixtures would be classified as Class III, Division 1.
An area where nonmetal combustible fibers/flyings are in the air under normal operating conditions in quantities sufficient to produce explosible mixtures would be classified as Class III, Division 1.
Explosionproof equipment is defined as equipment enclosed in a case capable of withstanding an explosion of a ___ gas or vapor.
Explosionproof equipment is defined as equipment enclosed in a case capable of withstanding an explosion of a ___ gas or vapor.
Protection technique concepts include what?
Protection technique concepts include what?
A Class II liquid has a flash point at or above ___ but below 140°F.
A Class II liquid has a flash point at or above ___ but below 140°F.
Article 505 of the NEC has ___ revisions in the 2023 edition.
Article 505 of the NEC has ___ revisions in the 2023 edition.
The flash point of a liquid is the minimum temperature at which it gives off vapor in ___ concentration.
The flash point of a liquid is the minimum temperature at which it gives off vapor in ___ concentration.
Explosionproof equipment must withstand hydrostatic pressure tests in a range of ___ the maximum pressure from an explosion within the enclosure.
Explosionproof equipment must withstand hydrostatic pressure tests in a range of ___ the maximum pressure from an explosion within the enclosure.
The purged and pressurized protection technique is permitted in any hazardous location for which it is ___.
The purged and pressurized protection technique is permitted in any hazardous location for which it is ___.
Combustible liquids will only form an ignitable mixture when they are heated above their ___.
Combustible liquids will only form an ignitable mixture when they are heated above their ___.
When explosions run through a conduit system, the gas in front creates a ___ that may result in extreme explosive and mechanical pressures.
When explosions run through a conduit system, the gas in front creates a ___ that may result in extreme explosive and mechanical pressures.
Which of the following methods is/are used to make plug-receptacle combinations safe for use in hazardous locations?
Which of the following methods is/are used to make plug-receptacle combinations safe for use in hazardous locations?
The ___ revision of the NEC added the word classified to Hazardous Locations.
The ___ revision of the NEC added the word classified to Hazardous Locations.
The use of ___ in hazardous locations is prohibited by the special bonding requirements.
The use of ___ in hazardous locations is prohibited by the special bonding requirements.
A Zone 0 location is a location in which ignitible concentrations of flammable gases or vapors are present ___.
A Zone 0 location is a location in which ignitible concentrations of flammable gases or vapors are present ___.
The first mention of hazardous locations appeared in the ___ edition of the NEC.
The first mention of hazardous locations appeared in the ___ edition of the NEC.
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Study Notes
Basic Conditions for Fires or Explosions
- Fires or explosions require at least three basic conditions to exist.
Hazardous Locations and Class/Division System
- All relevant materials would be found in the three location classes of the class/division system.
- Equipment with contacts like switches and circuit breakers can generate arcs or sparks, creating potential ignition sources under certain conditions.
Concentration and Ignition
- The concentration of a gas must increase from below the lower flammable limit to above the upper flammable limit for safety to be compromised.
- An ignitible mixture of flammable gases or combustible dusts with air can lead to fire or explosion if an ignition source is present.
Class and Division Designations
- Hazardous locations are categorized into 4 groups; Class I, Division 1 and Division 2 locations feature flammable gases or vapors.
- Class II locations deal with combustible dusts, with Class III focusing on areas with nonmetal combustible fibers in the air.
Equipment Specifications
- Explosionproof equipment must withstand potential explosions of specified gases or vapors within and prevent ignition of external flammable atmospheres.
- The concept of explosionproofing includes hydrostatic pressure testing to withstand pressures from potential internal explosions.
Flash Points and Temperatures
- A Class II liquid has a flash point between 100°F and 140°F.
- The flash point represents the minimum temperature for a substance to emit vapors in sufficient concentrations to create an ignitible mixture.
Regulations and Revisions
- Article 505 of the NEC included significant revisions with 135 updates as of 2023.
- The term "hazardous (classified) locations" was formalized in the 1975 revision of the NEC.
Zone Classifications
- Zone 0 locations have ignitible concentrations of flammable gases or vapors present continuously or for long durations.
- There are specific methods to safely use plug-receptacle combinations in hazardous locations, emphasizing adequate safety measures.
Historical Context
- The first mention of hazardous locations in the National Electrical Code (NEC) occurred in the 1920 edition.
- An alternate "zone classification" system was introduced in Article 505 in the NEC in 1996.
Additional Concepts
- The purged and pressurized protection technique is permissible in identified hazardous locations.
- Combustible liquids may form ignitible mixtures only when heated above their flash point.
- Pressure piling effects can occur in a conduit system during explosions, creating high mechanical pressures.
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