Lesson 1: Introduction To Hazardous (Classified) Locations

Question 1

Fires or explosions may only occur when ______ basic condition(s) exist(s).

a. 1
b. 2
c. 3
d. 4

Answer 1

c. 3

Question 2

Which of the following materials would be found in one of the three location classes of the class/division system?

I. Combustible dust
II. Combustible fibers/flyings
III. Combustible liquid-produced vapors
IV. Flammable gases
V. Flammable liquid-produced vapors
VI. Ignitible fibers/flyings

a. I. and II.
b. I., II., and III.
c. I., II., III., IV., and V.
d. All of the above

NEC REF:

Answer 2

d. All of the above

500.1

Question 3

The possibility that a gas mixture may be above the upper flammable limit does not ensure that the gas is safe. The gas must first pass through the flammable range as its ? increases from being below the lower flammable limit to a concentration above the upper flammable limit.

a. concentration
b. flash point
c. ignition temperature
d. none of the above

Answer 3

a. concentration

Question 4

A source of ignition is all that is needed to create a fire or an explosion when an ignitible or explosible mixture of a flammable gas or a combustible dust is mixed with air or oxygen in proportions that create an ignitible or explosible mixture.

True or False

Answer 4

True

Note: The answer to the question is true, but it must be understood it is also true for combustible liquid-produced vapors, flammable liquid-produced vapors, ignitible fibers/flyings, metal combustible fibers/flyings, and nonmetal combustible fibers/flyings.

Question 5

Equipment with contacts such as switches, circuit breakers, motor starters, pushbutton stations, and other similar equipment can produce arcs or sparks in normal operation when ? and become a potential ignition source.

a. contacts are closed
b. contacts are opened
c. the circuit is energized
d. both a. and b.

Answer 5

d. both a. and b.

Question 6

Materials in Class I, Division 1 and Division 2 hazardous (classification) locations are assigned to one of ______ groups.

a. 2
b. 3
c. 4
d. None of these

NEC REF:

Answer 6

c. 4

500.6(A)

Question 7

A Class I, Division 2 location is one in which flammable gases, flammable liquid-produced vapors, or combustible liquid-produced vapors ______.

I. are handled, processed, or used but normally confined within closed containers or systems
II. are in an area adjacent to a Class I, Division I location where positive-pressure ventilation prevents communication of the materials into the adjacent area
III. are normally prevented from becoming ignitible concentrations by using positive mechanical ventilation
IV. are not present

a. I. and II.
b. I., II., and III.
c. II. and III.
d. IV.

NEC REF:

Answer 7

b. I., II., and III.

500.5(B)(2)

Question 8

An alternate “zone classification” system found in Article ______ was added to the NEC in 1996.

a. 502
b. 503
c. 504
d. 505

Answer 8

d. 505

Note: The Zone System first appeared in the NEC in 1996 when Article 505 was added with a requirement that it could only be used under an engineer’s supervision. Article 505 covers the same hazards as Article 501 using an alternate method. The 1999 revision process removed the requirement to have an engineer supervise the use of Article 505. Six years later, the 2005 revision added Article 506, which covers combustible dusts and fibers/flyings.

Question 9

Metal combustible fibers/flyings are classified as ______.

a. Class II, Division 1, Group E
b. Class II, Division 1, Group F
c. Class II, Division 2, Group E
d. Class III, Division 1

NEC REF:

Answer 9

a. Class II, Division 1, Group E

500.5(D)(1)(a)

Question 10

The upper flammable limit is the highest ______ (or volume) concentration of a combustible substance in an oxidizing medium that will propagate a flame.

a. molar
b. possible
c. probable
d. ratio

Answer 10

a. molar

Question 11

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.

True or False

NEC REF:

Answer 11

True

500.5(D)(1)(a)

Note: Locations with nonmetal combustible fibers/flyings can be Division 1 or Division 2. The answer to this question is true because the question states the combustible fibers/flyings are in the air under normal operating conditions with a sufficient quantity to produce ignitible mixtures. This classifies the location as Class III Division 1. Metal combustible fibers/flyings are not included because they are classified as Class II, Division 1, Group E materials. The main intent of the question is to demonstrate that the NEC requirements for hazardous locations must be read carefully. Subsections 500.5(D)(1)(a) and 500.5(D)(2)(a) are very similar.

Question 12

Explosionproof equipment is defined as equipment enclosed in a case that is capable of withstanding an explosion of a ______ gas or vapor that may occur within it and of preventing the ignition of a specified gas or vapor surrounding the enclosure by sparks, flashes, or explosion of the gas or vapor within, and that operates at such an external temperature that a surrounding flammable atmosphere will not be ignited.

a. concentrated
b. flammable
c. hazardous
d. specified

NEC REF:

Answer 12

d. specified

100

Note: The answer to this question can be found in the NEC in Article 100. The 2023 NEC revision process moved every definition to Article 100, and many new definitions were added. Article 100 has over 800 definitions all in alphabetical order. The three parts in the 2020 edition have been removed.

Question 13

Protection technique concepts include ______.

I. Isolation of Electric Parts from Hazardous Materials
II. Prevention of External Ignition and Explosion
III. Prevention of Internal Ignition and Explosion
IV. Separation of Hazardous and Non-Hazardous Equipment

a. I. and II.
b. I., II., and III.
c. I., II., III., and IV.
d. I. and III.

Answer 13

b. I., II., and III.

Note: The protection technique concepts in the question categorize the protection techniques introduced in Articles 500, 505, and 506. They will be discussed in more detail in the lessons for these articles.

Question 14

A Class II liquid has a flash point at or above ______ but below 140°F.

a. 73°F
b. 100°F
c. 110°F
d. None of the above

Answer 14

b. 100°F

Question 15

Article 505 of the NEC has ______ revisions in the 2023 edition.

a. 19
b. 67
c. 89
d. 135

Answer 15

d. 135

Question 16

The flash point of a liquid is the minimum temperature at which it gives off vapor in ______ concentration to form an ignitible mixture with the air near the surface of the liquid, as specified by test.

a. a noxious
b. enriched
c. sufficient
d. the maximum

Answer 16

c. sufficient

Question 17

Explosionproof equipment must withstand hydrostatic pressure tests in a range of ______ the maximum pressure from an explosion within the enclosure.

a. 2 to 4 times
b. 3 to 6 ¹/₂ times
c. 4 to 6 ¹/₂ times
d. 6 ¹/₂ to 8 times

Answer 17

b. 3 to 6 ¹/₂ times

Note: Explosionproof enclosures must be manufactured to strict tolerances. This is accomplished by requiring the flanges and joints to be machined with very narrow tolerances. The concept is to allow the gases, which become hot in an internal explosion, to escape but also allowing them to cool to a point where there is not enough energy to cause an explosion when they come into contact with the hazardous atmosphere on the outside of the enclosure. This does not mean that the enclosure is required to be hermetically sealed.

Question 18

The purged and pressurized protection technique is permitted in any hazardous (classified) location for which it is ______.

a. approved
b. identified
c. labeled
d. listed
e. none of the above

NEC REF:

Answer 18

b. identified

500.7(D)

Question 19

Combustible liquids will only form an ignitible mixture when they are heated above their ______.

a. autoignition temperature
b. flash point
c. ignition temperature
d. none of the above

Answer 19

b. flash point

Question 20

When explosions run through a conduit system, the gas in front creates a ______ that may result in extreme explosive and mechanical pressures.

a. dangerous effect
b. disastrous effect
c. hazardous effect
d. pressure piling effect

Answer 20

d. pressure piling effect

Question 21

Which of the following methods is/are used to make plug-receptacle combinations safe for use in hazardous (classified) locations?

I. Delayed action
II. Explosionproof enclosures
III. Interlocked, dead front

a. I.
b. I., II., and III.
c. I. and III.
d. II.

Answer 21

c. I. and III.

Question 22

The ______ revision of the NEC added the word classified to Hazardous (Classified) Locations.

a. 1925
b. 1931
c. 1975
d. 1987

Answer 22

c. 1975

Question 23

The use of ______ in hazardous locations is prohibited by the special bonding requirements for hazardous locations.

I. bonding jumpers over 12” in length
II. double locknuts
III. locknut bushings

a. I.
b. II.
c. II. and III.
d. III.

Answer 23

c. II. and III.

Question 24

A Zone 0 location is a location in which ignitible concentrations of flammable gases or vapors are present ______.

I. continuously
II. for long periods of time
III. frequently

a. I. and II.
b. I., II., and III.
c. I. and III.
d. II. and III.

NEC REF:

Answer 24

a. I. and II.

505.5(B)(1)

Question 25

The first mention of hazardous locations appeared in the ______ edition of the NEC. a. 1897 b. 1920 c. 1947 d. 1950

Answer 25

b. 1920

Question 26

Article 506 which covers the Zone System requirements for the Class/Division hazards in Article 502 and Article 503 was added to the NEC in ______. a. 1996 b. 1999 c. 2005 d. 2008

Answer 26

c. 2005

Question 27

In the ______ NEC revision, the requirements for hazardous locations were reformatted into four articles: 500, 501, 502, and 503. a. 1925 b. 1947 c. 1950 d. 1959

Answer 27

d. 1959

Question 28

Article 510, created in 1953 for six special occupancies and revised in 1959 by moving the six special occupancies to separate new articles, was finally deleted in ______. a. 2000 b. 2014 c. 2020 d. 2023

Answer 28

d. 2023

Question 29

The point where a flammable or combustible substance is capable of ignition depends on the substance type and which of the following? I. The autoignition temperature of the substance II. The flash point of the substance III. The lower flammable limit of the substance IV. The upper flammable limit of the substance a. I., II., and III. b. I., II., and IV. c. II., III., and IV. d. I., II., III., and IV.

Answer 29

c. II., III., and IV.

Question 30

Refrigerant machinery rooms containing ammonia refrigeration systems are permitted to be classified as unclassified locations where they have adequate mechanical ventilation that operates continuously, or where a detection system initiates the ventilation where the ammonia concentration reaches ______. a. 100 ppm b. 125 ppm c. 150 ppm d. 175 ppm

Answer 30

c. 150 ppm

Question 31

The special bonding requirements of the “dot” 30(B)(2)(a) subdivisions of Articles 501, 502, 503, 505, and 506 require an equipment bonding jumper of the wire type complying with 250.102 to be installed in ______. I. flexible metal conduit II. intermediate metal conduit III. liquidtight metal conduit IV. rigid metal conduit a. I. b. I. and II. c. I. and III. d. I., II., III., and IV.

Answer 31

c. I. and III.

Question 32

The bonding requirement in “dot” 30(B)(2)(b) is not required for listed liquidtight flexible metal conduit 6 feet or less in length, installed with fitting listed for grounding, with the overcurrent protection rated ______ amperes or less, and the load is part of a meter, instrument, or relay circuit. a. 5 b. 10 c. 12 d. 15

Answer 32

b. 10

Question 33

Grounding in hazardous locations must comply with the requirements of ______ of Article 250. a. Parts I. and II. b. Parts I. and IV. c. Parts I. and VI. d. Parts I. and VII. e. Parts I., II., and IV.

Answer 33

c. Parts I. and VI. Note: See NEC 501.30(A).

Question 34

Explosionproof or dust-ignitionproof equipment is not permitted for use at temperatures lower than ______ unless they are identified for low-temperature service. a. 13°C b. −13°C c. −13°F d. −25°F

Answer 34

c. −13°F