Temperature T Class Ratings in Hazardous Area

 

1. What is the function of T class ratings for explosion-proof products in hazardous area?

 

Temperature Classifications are given to hazardous area Temperature Class Ratings (also known as T-ratings or T-Class) and are applied to hazardous area zones and electrical equipment – T Class Ratings are utilized for all hazardous areas and explosion protection methods.

 

This helps the user to quantify the level of thermal energy allowed in the hazardous area area or explosive atmosphere according to the ATEX Directive or produced by the hazardous area equipment.

 

2. Why is it important to definite the T class rating in hazardous area?

 

According to the ATEX Directive, A hazardous area can be defined as any location where there is risk of an explosion due to the presence of flammable gas and steam. However it is important to remember that every hazardous area is different and each has specific requirements depending on the nature of the atmosphere and the elements that are present.

 

Flammable materials have a temperature at which ignition will take place, even in the absence of an external source. The ignition temperature is the lowest temperature on the surface at which an explosive atmosphere will ignite. Apparatus must be selected so that it will not expose a gas-air mixture to a temperature exceeding its ignition temperature. This is achieved by Temperature Classification, the T-Class.

 

Gases and dusts have been divided into temperature classes according to their ignition temperatures so that electrical equipment can be further sub-divided into six temperature classes T1 to T6.

 

Note: The maximum operating surface temperature of a piece of electrical equipment must always be below the ignition temperature of the explosive mixture.

 

3. What is the Temperature Class of explosion-proof maximum surface temperature?

 

Temperature Classification is based on the maximum temperature which any relevant part of the equipment which may be in contact with a flammable or explosive gas can reach.

 

This classification identifies the minimum ignition temperature threshold for the hazardous area. In other words, in order for the explosive or combustible environment to ignite, it need to bear temperature which excess of this value. The values applied to this T-Class classification run from T1 to T6:

 

T1 Class     450°C

T2 Class     300°C

T3 Class     200°C

T4 Class     135°C

T5 Class     100°C

T6 Class      85°C

 

Relationship between T class and the maximum permissible temperature in °C of any surface in contact with flammable gas or ignitable dust is based on –20°C to +40°C ambient air temperature.

 

T1 class means the minimum ignition temperature is more than 450°C and T6 class means the minimum ignition temperature is more than 85°C.

 

4. What is the matched standard of T rating equipment?

 

An electrical equipment in hazardous area could be designed for used in higher ambient temperatures. This would indicated on the rating plate e.g. Exd ib IIC T6 G6/Ext DA21 IP66 T80°C– it is from Ningbo Joiwo Explosionproof telephones rating late, which means at 60°C ambient air temperature, T6 will not be exceeded, with the highest T class division.

 

Gas Area Classified T Rating	Suitable Equipment
T1	T1, T2, T3, T4, T5, T6
T2	T2, T3, T4, T5, T6
T3	T3, T4, T5, T6
T4	T4, T5, T6
T5	T5, T6
T6	T6

 

 

T1 class means the maximum surface temperature generated by the instrument at 40° C is 450° C. T6 class means the maximum surface temperature generated by the equipment is 85° C.

 

Assuming the associated T Class and Temperature rating for the equipment are appropriate for the area, you could always use an instrument with a more stringent Division rating than required for the area.