Temperature Class
With an air/gas mixture (not oxygen enriched) in a combustible concentration, an ignition source must be present to complete the hazardous condition. |
|
Temperature
Classification |
| Marking |
Zone |
Division |
| T1 |
450ºC |
450ºC |
| T2 |
300ºC |
300ºC |
| T2A |
|
280ºC |
| T2B |
|
260ºC |
| T2C |
|
230ºC |
| T2D |
|
215ºC |
| T3 |
200ºC |
200ºC |
| T3A |
|
180ºC |
| T3B |
|
165ºC |
| T3C |
135ºC |
135ºC |
| T4 |
135ºC |
135ºC |
| T4A |
100ºC |
100ºC |
| T5 |
100ºC |
100ºC |
| T6 |
85ºC |
85ºC |
The chart above shows temperature
classifications in the Zone System and the Division System. These represent the
maximum allowable temperatures for equipment installed in a classified location and represent the minimum temperatures for ignition of specified gases.
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LEL & UEL
The LEL (Lower Explosive Limit) is defined as “a mixture of gas and air in which the gas quantity is BELOW the required
amount to ignite.” The UEL (Upper Explosive Limit) is the gas/air mixture ABOVE that range, i.e. gas poor, gas rich.
The area between the LEL and UEL is the
“explosive range” or “flammable range”. The words explosive and flammable are interchangeable for LEL and UEL purposes.
Flash Point
The Flash Point of a liquid is defined as the lowest
temperature at which sufficient vapor given off the
liquid can ignite. These are just a few of |
|
Flash
Points For Typical Liquids |
| Hydrogen - 429ºF |
Propane -155ºF |
| Acetylene -116ºF |
Gasoline -45ºF |
| Acetone -
118ºF |
Butane -75ºF |
the
temperatures at
which a fire or explosion can occur.
Comprehensive lists of gases and specifics that relate to those
gases can be found in several international publications that
correlate with the specific codes that pertain to that area.
For a guide in determining when
flammable gases or vapors are present continuously or for long
periods:
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Recommended Practice for
Classification of Locations for Electrical Installations of
Petroleum Facilities for Zone 0, Zone 1 or Zone 2, API RP
505-96; Electrical Apparatus for Explosive Gas Atmospheres,
Classifications of Hazardous Areas, IEC 79-10; and Area
Classification Code for Petroleum Installations, Model Code Part
15, Institute of Petroleum: and Electrical
Apparatus (Classified) Locations, ISA S12.24.01-1997.
The U.S. uses the word “LOCATION” to define a place
that is classified as hazardous while under the IEC the word
“AREA” is used. The words are interchangeable in relation to
a place that may be deemed hazardous in relation to
ignitable gases. |
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