Dust ignition protection by enclosure Ex t

Testing technique

We assess, test and certify equipment for dust ignition protection by enclosure Ex t. 

This determines if the electrical equipment enclosure prevents the ingress of dust into the enclosure. Also that the electrical equipment is limiting surface temperatures so as to prevent an explosion when the equipment is surrounded with combustible dust or layer or cloud. 

Combustible dusts are those dusts which may form explosive mixtures with air at standard atmospheric pressure and temperature. 

Dust explosions may be initiated by ignition of either a layer of dust or a cloud of dust. 

Testing to standards  

The International standard IEC 60079-31 or Australian/New Zealand standard AS/NZS 60079.31 specifies requirements for design, construction and testing of Ex equipment. 

Ex components for type of protection Ex t are always applied together with the standard IEC (or AS/NZS) 60079-0 for explosive atmospheres for equipment - general requirements. 

Equipment Level Protections  

Equipment Level Protection (ELP) ‘t’ is divided into three levels, based on the risk of the electrical equipment becoming an ignition source in an explosive dust atmosphere:  

1. ‘ta’ - EPL Da, “very high” level of protection, where equipment is not a source of ignition in normal operation, during expected malfunctions or during rare malfunctions 
2. ‘tb’ - EPL Db, “high” level of protection, where equipment is not a source of ignition in normal operation or during expected malfunctions 
3. ‘tc’ - EPL Dc, “enhanced” level of protection, where equipment is not a source of ignition in normal operation. 

Equipment of Groups 

Equipment of Group III is intended for use in areas with an explosive dust atmosphere, other than mines susceptible to firedamp. 

Group III is divided into 3 subgroups based on dust particle sizes and electrical resistivity: 

1. IIIA: combustible flyings, requires IP6X for ‘ta’ and IP5X for ‘tb’ and ‘tc’ 
2. IIIB: non-conductive dust, requires IP6X for ‘ta’ and IP6X for ‘tb’ and IP5X for ‘tc’ 
3. IIIC: conductive dust, requires IP6X for ‘ta’, ‘tb’ and ‘tc’. 

If equipment is intended for level of protection ‘ta’, additional protective devices shall be used.  

If equipment incorporates normally arcing and sparking parts, these parts shall be protected with additional enclosure, which shall comply with level protection ‘tc’.  

Types of tests 

Here are some tests that may be applicable depending on the construction and material of equipment:  

• thermal tests without dust layer and with dust layer 

• thermal endurance to heat and to cold 

• impact tests 

• drop tests

• pressure test 

• degree of protection IP tests 

• surface resistance test 

• earth continuity test 

• measurement of Capacitance test 

• resistance to UV test. 

Getting the test results

The results of our testing are presented in a test report that is endorsed by our local Australian laboratory accreditation body, NATA (National Association of Testing Authorities, Australia).

When product sample testing, design assessment (Ex test report) and quality assessment (quality assessment report) are successfully completed, an Ex Certificate of Conformity (IECEx or ANZEx) is issued by TestSafe.

Help and support

Complete our online enquiry form.

Call: +61 (2) 4724 4900

Email: testsafe@safework.nsw.gov.au

Mail us at: PO Box 592, Richmond, NSW 2753 Australia.