A hazardous environment or location is some combustible materials that could easily ignite and create a fire hazard. Electric motors operated in such an environment need to be carefully specified and selected in order not to pose an explosion threat to an installation.
Arcs, sparks and high temperatures on the surfaces of electric motors are common sources of ignition of hazardous substances. Therefore the right motors need to be specified and selected for use in this kind of environments otherwise the consequences of an explosion and eventual fire resulting from using the wrong kind of motor could range from minor injuries, production down time and destruction of valuable investment as well as death.
Information Required to Specify an Electric Motor for Use in Hazardous Locations
Four basic information are required to specify and select the right motor for use in a hazardous environment:
1. Class of materials in the hazardous environment
2. Division classification of the hazardous environment
3. Group classification of the hazardous environment
4. The autoignition temperature (AIT) of the hazardous material in the environment
 |
| How to Select Electric Motors for Use in Hazardous Locations |
Class of Materials in the Hazardous Environment.
There are three classes of hazardous locations according to the NEC and CEC:
| Class Location | Hazardous Materials Present |
|---|---|
| I | Contains flammable gases or vapors e.g Hydrocarbon gases |
| II | Contains dusts either electrically conductive or explosive in air |
| III | Contains filings and flyings that are easily ignitable e.g texile industry |
*NEC - National Electric Code
*CEC - Canadian Electrical Code
Division of the Hazardous Environment
Division describes the condition under which the hazardous material is present in the particular environment. There are two basic divisions: Division 1 and Division 2 locations
| Division 1 Location |
|---|
| A Division 1 location is one where an explosive or ignitable material is present under normal operating condition. Division 1 locations include environment where explosive materials are routinely exposed to the environment during regular operation and scheduled maintenance. |
| Division 2 Location |
|---|
| A Division 2 location is one where hazardous substances are stored or handled under abnormal conditions. |
Group Classification of Hazardous Environment.
Class I and Class II are divided into groups according to the behaviour of the hazardous material after it has been ignited. These groupings are shown below:
| Class Location | Groups |
|---|---|
| I | A, B, C, D |
| II | E, F, G |
Autoignition Temperature of Hazardous Materials
A key information required to accurately specify an electric motor in a hazardous environment is the autoignition temperature of the hazardous material, AIT for short.
The AIT refers to the minimum temperature at which there is sufficient energy for a hazardous material (chemical) to ignite spontaneously in the absence of a spark, flame or other source of ignition. The AITs of various Class I and Class II hazardous materials are shown in the table below:
| *Class | Group | Hazardous Material |
Autoignition Temperature
|
|
|---|---|---|---|---|
| °C | °F | |||
| I | A | Acetylene |
305
|
581
|
| B | Butadiene |
420
|
788
|
|
| Ethlylene Oxide |
570
|
1,058
|
||
| Hydrogen |
500
|
932
|
||
| C | Acetaldehyde |
175
|
347
|
|
| Cyclopropane |
498
|
928
|
||
| Diethyl Ether |
180
|
356
|
||
| Ethylene |
450
|
842
|
||
| Isoprene |
398
|
743
|
||
| D | Acetone |
465
|
869
|
|
| Amonia |
651
|
1,204
|
||
| Benzene |
498
|
928
|
||
| Butane |
287
|
550
|
||
| Ethane |
472
|
882
|
||
| Ethanol |
363
|
685
|
||
| Gasoline |
246 - 280
|
475 - 536
|
||
| Methane |
537
|
999
|
||
| Propane |
450
|
842
|
||
| Styrene |
490
|
914
|
||
| II | E | Aluminium |
650
|
1,202
|
| Bronze |
370
|
698
|
||
| Chromium |
580
|
1,078
|
||
| Magnesium |
620
|
1,148
|
||
| Titanium |
330
|
626
|
||
| Zinc |
630
|
1,166
|
||
| F | Coal |
610
|
1,130
|
|
| G | Corn |
400
|
752
|
|
| Nylon |
500
|
932
|
||
| Polyethylene |
450
|
842
|
||
| Sugar |
350
|
662
|
||
| Wheat |
480
|
896
|
||
| Wheat Flower |
380
|
716
|
||
*Source : American Institute of Chemical Engineers (AIChE) - www.aiche.org
Characteristics of Motors in Class I, Division 1 & 2 Hazardous Locations
To be able to apply an electric motor successfully in a hazardous environment, these motors must possess certain critical characteristics that make them suitable to operate in these environment without creating problems.
- These motors must be built and labelled as explosion-proof
- An explosion-proof motor must contain an internal explosion without rupturing
- An explosion-proof motor must have flame paths for exhausting hazardous gases during an explosion and for cooling the hazardous material as they leave the motor to prevent further explosion.
- The more severe the explosion hazards, the stronger the enclosures of the motor and the longer the flame paths. For example, motors for use in group A environment which has acetylene gas require the highest enclosure strength and longest flame paths compared with those used in group D environment with only propane gas.
- Motors for use in hazardous environment are assigned a temperature code (T-Code), an identification number which describes the maximum temperature of surfaces subject to contact with hazardous materials. The temperature value defined by the T-code applies under all conditions of motor operation including burnt out, overload and locked rotor current.
- The T-code for a given motor must be less than the AIT of the hazardous gas or mixture in the environment where the motor operates. This is to ensure that the hazardous materials do not spontaneously ignite when it contacts the motor surfaces and enclosure during operation.
Temperature Codes of Motors Operating in Hazardous Locations According to NEC, CEC & IEC Designations:
The table below gives the temperature codes for motors operating in hazardous environment according to NEC/CEC & IEC letter designations are given in the table below:
| **NEC/CEC Designation T - Code |
IEC Designation T - Code |
Maximum Surface Temperature | |
|---|---|---|---|
°C
|
°F
|
||
T1
|
T1
|
450
|
842
|
T2
|
T2
|
300
|
572
|
T2A
|
280
|
536
|
|
T2B
|
260
|
500
|
|
T2C
|
230
|
446
|
|
T2D
|
215
|
419
|
|
T3
|
200
|
392
|
|
T3A
|
T3
|
180
|
356
|
T3B
|
165
|
329
|
|
T3C
|
160
|
320
|
|
T4
|
T4
|
135
|
275
|
T4A
|
120
|
248
|
|
T5
|
T5
|
100
|
212
|
T6
|
T6
|
85
|
185
|
**Source : American Institute of Chemical Engineers (AIChE) - www.aiche.org
Class I, Division 2 Motors
The minimum requirements for motors for use in Class I, Division 2 locations are less stringent than those for use in Class I, Division 1 locations. Some basic characteristics and requirement for motors for use in Class I, Division 2 locations are enumerated below:
- An explosion-proof motor certified for use in a Class I, Division 1 location may also be operated in a Class I, Division 2 area provided the motor meets the group and T-Code requirements.
- TEFC (Totally Enclosed, Fan Cooled) motors and ODP (Open Drip -proof) motors can be used in Division 2 locations provided they do not have ignition sources such as arc-producing brushes or switching mechanisms.
- Three-phase induction motors with low surface temperatures and no sparking parts can be used in Division 2 locations.
Characteristics of Motors for use in Class II locations
- As class II locations contain ignitable dusts, electric motors operating in this kind of environment must be dust-ignition-proof.
- The enclosures of dust-ignition-proof motors are designed to exclude hazardous materials from accessing the internals of the motors unlike explosion-proof motors.
- The T-code of a dust-ignition-proof motor must correspond to a maximum surface temperature below the AIT of the hazardous dust materials.
Nameplate Requirements for Motors Operating in Hazardous Locations
Selecting the right kind of motor that meets the requirements for use in hazardous environment is not an easy task. However, manufacturers of electric motors for use in hazardous locations have standard nameplates that contain the following information:
(a) Type of Enclosure of Motor
(b) Class of hazardous materials for which the motor is suitable
(c) Group of the hazardous materials
(d) T-code of the electric motor
The above information makes it less tedious in selecting and specifying a motor for use in a hazardous environment.