Intrinsic safety Ex i

Test technique  

Intrinsic safety assessment and tests are carried out to analyse whether or not equipment is capable of causing ignition in explosive atmospheres. 

Each circuit is analysed and assessed under normal operation and specified fault conditions against spark ignition, thermal ignition and stored energy level permitted by the representation of gas or vapour application. 

Testing to standards and requirements  

Any products and designs that are submitted to us for assessment and testing to 'intrinsic safety' type of explosion protection are examined to the requirements of International standard IEC 60079-11, or Australian/New Zealand standard AS/NZS 60079.11, in conjunction with  the standard IEC (or AS/NZS) 60079-0 for explosive atmospheres for  equipment - General requirements. 

For intrinsically safe electrical systems we can also assess and test to International standard IEC 60079-25, or Australian/New Zealand standard AS/NZS 60079.25. This is always applied together with the standards IEC (or AS/NZS) 60079-0 for explosive atmospheres for  equipment - General requirements and IEC (or AS/NZS)  60079-11. 

Levels of protection  

Intrinsically safe apparatus and intrinsically safe part of associated apparatus are categorised into three levels of protection:

1. ‘ia’ - equipment with this level of protection shall not be capable of causing ignition in normal operation, and with application of two countable faults plus those non-countable faults.
2. ‘ib’ - equipment with this level of protection shall not be capable of causing ignition in normal operation, and with application of one countable fault plus those non-countable faults.
3. ‘ic’: equipment with this level of protection shall not be capable of causing ignition in normal operation.

Examination process 

The circuit design is examined by reviewing the circuit schematics, interconnections diagrams and circuit board layouts.  

Most of this work is desktop assessment using the knowledge of experts who have a design background and a complete knowledge of the intrinsic safety Standards. 

The actual circuit board(s) (or an equivalent circuit made up in our laboratory which represents the most onerous case in the assessment) is then subjected to tests on the spark test apparatus. 

Explosive gases are mixed and piped into this apparatus, and wires from the circuit outputs are connected to an arrangement of tungsten wires being brought intermittently into contact with a cadmium disk (which is mounted on a rotating shaft).  

The purpose is to 'make and break' the circuit 1600 times inside an explosive atmosphere to check if the energy in the circuit may cause an ignition. 

For thermal ignition assessment, we carry out temperature rise tests to measure the maximum temperature rise on the surface of the components, and to confirm that the temperature is less than the explosive gas could ignite. The faults count is applied depending on the category of protection.  

The critical spacing distances on the electronic printed wiring board are measured on a computer using a Gerber file and the relevant software. 

To test that the internal circuits are adequately insulated from any metallic parts that may not be grounded, a high voltage test is applied between the metallic enclosure and the internal circuit. 

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

• thermal endurance to heat and cold 

• resistance to chemical agents for Group I 

• impact test 

• drop test 

• IP test 

• impact test on piezo-electric devices 

• battery short circuit test 

• small component ignition test 

• optical isolators tests 

• clearance and creepage distances measurement. 

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.