Equipment protection by special protections Ex s
Special protection ‘s’ allows certification and testing for design of a product that cannot comply in full with recognised types of protection. It's also relevant where the standards for the recognized types of protection do not cover the required operating conditions.
About the protection
Special protection ‘s’ allows certification and testing for design of a product that cannot comply in full with recognised types of protection.
It is also relevant where the standards for the recognized types of protection do not cover the required operating conditions. For example, outside normal atmospheric temperature and/or pressure and/or oxygen concentration or, used in hybrid mixture of dust and gas.
Testing to standards
The International Standard IEC 60079-33 or Australian/New Zealand Standard AS/NZS 60079.33 specifies the basic method on how the compliance can be achieved. It is applied in conjunction with the general requirements standard IEC 60079-0 or AS/NZS 60079.0.
Here are some techniques that Ex s can be achieved, using one or a combination:
containment of internal explosion
exclusion of explosive atmosphere
avoidance of ignition sources
energy limitation, both sparking and thermal
Documentation required from the manufacturer
Here are some documents the manufacturer needs to provide:
details of considerations given to the possibilities for design to the recognised types of protection (or combination of types of protection), before proceeding to special protection
aspects that are covered by the standards for any recognised type of protection applied, for those aspect that are not covered by verification to recognised types of protection
drawings that provide full specifications and details relevant to Ex s protection
draft ignition hazards assessment, which is used to develop required test plan
Failure Mode and Effects Analysis (FMEA).
Ignition hazards assessment
The ignition hazards assessment needs to identify all potential ignition sources that can occur and list control measures that are applied to reduce the likelihood of a potential ignition source becoming an effective ignition source.
Here are some possible ignition sources:
high surface temperatures
radio frequency electromagnetic waves
electromagnetic waves including optical radiation
Levels of protection
Levels of protection ‘s’ is divided into three Levels of protection based on the risk of the electrical equipment becoming an ignition source in an explosive dust or gas atmosphere:
- ‘sa’ - EPL Ma, or Ga, or Da, “very high” level of protection, where equipment is not a source of ignition in normal operation, during expected malfunctions or during rare malfunctions
- ‘sb’ - EPL Mb or Gb or Db, “high” level of protection, where equipment is not a source of ignition in normal operation or during expected malfunctions
- ‘sc’ - EPL Gc or Dc, “enhanced” level of protection, where equipment is not a source of ignition in normal operation.
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.
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