15.4 Tests of flameproof enclosures with breathing and draining devices
The tests in accordance with 15.4.1 to 15.4.3 shall be carried out in the following order on a
sample after the impact strength test of 10.8.
For devices with non-measurable paths, the maximum bubble test pore size of the sample shall
not be less than 85 % of the specified maximum bubble test pore size. See Annex B.
15.4.1 Tests of ability of the enclosure to withstand pressure
The tests shall be made in accordance with 15.1 with the following additions and modifications.
15.4.1.1 For the determination of the explosion pressure in accordance with 15.1.2, breathing
and draining devices shall be replaced by solid plugs.
15.4.1.2 For the overpressure test in accordance with 15.1.3, a thin flexible membrane
(for example, a thin plastic sheet) shall be fitted to the inner surfaces of the breathing and
draining devices. After the overpressure test, the device shall show no permanent deformation
or damage likely to affect the type of protection.
15.4.2 Thermal tests
15.4.2.1 Test procedure
The enclosure, with the device(s) fitted, shall be tested in accordance with the method 15.4.3.1
but with the ignition source only in the position giving the most unfavourable thermal results.
The temperature of the external surface of the device(s) shall be monitored during the test. The
test shall be carried out five times. The test mixture to be used shall be (4,2 ± 0,1) % propane
in volumetric ratio with air and at atmospheric pressure. Additionally, for devices intended for
use in acetylene, (7,5 ± 0,1) % acetylene in volumetric ratio with air and at atmospheric
pressure shall be used.
In an enclosure where there is the possibility of a forced or induced flow of a potentially
dangerous gas, the enclosure shall be arranged during the tests so that the gas can flow
through the device(s) and the enclosure.
Any ventilation or sampling system shall be operated as specified in the manufacturer's
documentation. After each of the five tests, the external explosive mixture shall be maintained
for a sufficient time to allow any continuous burning on the face of the device to become
evident (for example, for at least 10 min so as to increase the temperature of the external
surface of the device or to make heat transfer to the outer face possible).
15.4.2.2 Acceptance criterion
No continuous burning shall be observed. No flame transmission shall occur. The measured
external surface temperature rise of the device shall be multiplied by a safety factor of 1,2 for
the determination of the temperature class of the electrical apparatus.