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Buxton, at the heart of England’s Peak District National Park, remains famous for the official announcement that “Snow Stopped Play” during a first-class cricket match in June 1975.

Snowy Field

Although snow in June is exceptional, residents of Buxton are used to their own micro-climate, with temperatures typically between two and three degrees cooler than the nearest town, Macclesfield, which is about 300 metres nearer sea level.

SGS’s Buxton-based Ex testing laboratory, one of the largest organizations in the world to boast a laboratory dedicated to the certification of equipment intended for installation in hazardous atmospheres, has now invested in going significantly colder!

The laboratory has acquired a state-of-the-art freezer which is capable of operating down to -70°C and large enough to contain extremely bulky equipment. An example being a 630 frame-size motor, rated at 3 MW, that can be switched on and rotating at full speed whilst an explosive gas atmosphere is ignited inside it.

To anyone unfamiliar with the testing of equipment for hazardous atmospheres, this can seem an odd requirement, but it is just part of the bread and butter activity of one of the best known Ex testing laboratories in the world.

A necessity of the “flameproof” protection concept for Ex Equipment is that the maximum potential internal explosion pressure is determined in a series of tests, followed by a hydraulic over-pressure test, to ensure that the equipment enclosure will not burst. As ambient temperatures decrease, more and more gas molecules can fit in a given enclosure size, so that when the ignition occurs, the final pressure is multiplied by that increase in the amount of gas. Unfortunately, because of the way that explosions develop in complex shapes, there is not a single mathematical equation that can enable the result to be calculated. Hence the need for the practical test to be undertaken at the actual minimum ambient temperature.

For many years, the lowest temperature requested was minus 50 degrees, but with the advent of more oil exploration in arctic areas, this has fallen even further to minus 65 degrees.

Once the hydraulic over-pressure test (sometimes with internal pressures in excess of 100 bar) has successfully taken place the enclosure is subjected to the test for “non-transmission” where the enclosure has the gas atmosphere both inside and outside and an internal ignition must not ignite the outside atmosphere.

SGS has carefully worked safety procedures for such gas explosions. Interestingly, though the tests may sound dangerous, they are far more predictable than “short-circuit” tests on batteries and cells of portable equipment where the internal protective devices have been removed, as required by the standard for Intrinsic Safety protection.

While some cells can behave comparatively benignly, experience suggests extreme caution when testing some lithium-based batteries. In a recent test, the cells registered a temperature of over 500°C and there was need to employ a special “lithium” fire extinguisher to quell the flames.

Whilst SGS can advise customers as to the likely outcome of such tests, they have an absolute right to insist that the test program proceeds as laid down in the standard, leaving no option but to devise safety procedures.

SGS is prolific in issuing European ATEX Directive Certification and, in addition, has issued more international certificates in the IECEX Certification System than any other laboratory in the world.

Where local certification is required, such as in Brazil or Russia, the SGS Baseefa IECEx Certificate and Report are used to underpin that local certification.

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For more information, please contact:

Carolyn Featherstone
SGS
Business Development Manager
t: +44 01 298 76 66 00

Author:

Ron Sinclair
SGS
Technical Manager
t: +44 01 298 76 66 00