Machines for EU safety footwear testing – part 10
Continuing our description of test equipment that can be used to assess footwear in line with the European PPE standard.
by Peter Allen
This article concludes a series considering SATRA test equipment that can be used to conduct the tests specified in the European safety footwear standard EN ISO 20345:2011- ‘Personal protective equipment – safety footwear’. The first five articles in this series covered ‘basic requirements’, and subsequent articles examined the test equipment which can be used to conduct the tests as set out in clause 6 of EN ISO 20345:2011 – ‘Additional requirements for safety footwear’.
This final article explains additional requirements for uppers and outsoles. For uppers there is one additional requirement: ‘water penetration and absorption’ (clause 6.3), and for outsoles there are two additional requirements: ‘resistance to hot contact’ (clause 6.4.1) and ‘resistance to fuel oil’ (clause 6.4.2). The first of these – water penetration and absorption – is only applicable to Class I footwear (made with leather, textiles and/or synthetic uppers). The two outsole requirements are applicable to Class I as well as Class II products (all-polymeric moulded), as defined in the standard.
Additional requirements can be necessary for safety footwear, depending on the hazards to be encountered at the workplace. In such cases, safety footwear must conform to the appropriate additional requirements and can be marked with the relevant symbols set out in table 18 of EN ISO 20345. These symbols allow the customer to identify the additional hazards for which the footwear is appropriate.
Water penetration and absorption
The requirements for ‘Upper – water penetration and absorption’ are set out in clause 6.3 of EN ISO 20345:2011. This states that, when tested in accordance with EN ISO 20344:2011 clause 6.13, after 60 minutes the water penetration shall not be greater than 0.2g and the water absorption shall not be higher than 30 per cent. The SATRA STM 703 Bally penetrometer test machine (figure 1) allows testing to be carried out which meets the requirements set out in clause 6.13 of EN ISO 20344:2011. This is a four-station machine allowing four specimens to be tested at the same time. At each station, a rectangular test piece of the material to be assessed is clamped at each end of the material around two 30mm diameter coaxially-aligned cylinders. One cylinder is fixed and the other moves cyclically along the direction of the axis. The specimen forms a trough open at the top. The lower part of the specimen is partially immersed in a shallow tank of distilled water.
During the test, the test piece is cyclically compressed and relaxed by the relative movement between the cylinders to which the material is clamped, at a rate of 50 cycles a minute. This is a relatively gentle water resistance test, as only a 7.5 per cent compression of the test piece is specified. An absorbent cloth of defined size and area density is lightly held in place inside the specimen trough and is used to absorb any water transmitted to the interior of the trough through the specimen in the 60 minutes’ duration of the test. Weighing the absorbent cloth and the test piece before and after the test allows the water transmission and water absorption to be calculated. Footwear which meets the requirements of this test can be marked with the symbol ‘WRU’.
Resistance to hot contact
The first of the ‘additional requirements’ for solings is set out in EN ISO 20345:2011 clause 6.4.1 (‘resistance to hot contact’). This states that, when tested in accordance with ISO 20344:2011 clause 8.7, rubber and polymeric outsoles shall not melt and shall not develop cracks when subsequently bent around a specified mandrel. This test can be performed on the SATRA STM 455 heat resistance tester (figure 2), which comprises an electrically heated head of defined mass and geometry incorporating a 25.5mm square contact face. The head is mounted on a swinging arm arranged to apply a pressure of 20kPa over the contact face when the arm is lowered onto the test specimen.
In preparation for a test, the head is heated electrically up to a temperature just over 300°C, which is displayed on a temperature gauge incorporated into the STM 455 unit. During this heating stage, the heat contact surface of the head rests on an insulated pad mounted on a support above and clear of the item to be assessed. A 30mm x 70mm test specimen is cut from the sole and any cleats are removed. This is placed (with the lower surface of the sole uppermost) on an anvil below the insulating support. A piece of aluminium foil is placed over the surface of the test piece to protect the head from sticking to the test piece or becoming otherwise contaminated. When the temperature has just exceeded 300°C, the heat to the element is turned off and the head is allowed to cool until it is at 300°C. At this point, the insulated support is swung out of the way and the head is lowered onto the test specimen. The contact is maintained for 60 seconds before the heated head is lifted clear. The foil is then peeled from the specimen, which is allowed to cool for ten minutes before being examined. The test piece is inspected against criteria set out in the standard before and after being bent around a 10mm diameter steel mandrel. Footwear which meets the requirements of this test can be marked with the symbol ‘HRO’.
Resistance to fuel oil
Fuel oil and related solvents can have a detrimental effect on the soles of footwear. EN ISO 20345:2011 clause 6.4.1 – ‘Resistance to fuel oil’ establishes the requirements to be applied to safety footwear intended for situations where the sole may come into contact with fuel oil. EN ISO 20345:2011 clause 6.4.1 sets out an initial requirement which, when tested to EN ISO 20344:2011 clause 8.6.1, allows the determination of the increase in volume of a specimen of soling after a period of immersion in the designated liquid. Any increase in volume (swelling) should not be more than 12 per cent.
To conduct the test to EN ISO 20344:2011 clause 8.6.1, two cylindrical specimens of 16mm diameter and 4mm thickness are cut from the outsole. Initial weight measurements are taken of the test pieces in air and distilled water as set out in ISO 1817:20111 clause 8.3. This allows the calculation of any change in volume by a water displacement method. The specimens are then immersed in the designated test liquid (2,2,4-trimethylpentane), at 23°C for a period of 22 hours and then re-weighed in air and water. The change in volume of the specimen after immersion in the test liquid can be determined from these readings.
If after this testing, the test piece shrinks by more than 1 per cent in volume or increases in hardness by more than 10 Shore ‘A’ hardness units, a further test is required in accordance with the method described in ISO 20344:2011 clause 8.6.2 – ‘Method for outsoles materials which shrink or become hardened’. The hardness of the test piece can be recorded using a SATRA STD 226 digital durometer fitted with a Shore A scale module (figure 3). Measurements are taken before and after the specimen is immersed in the test liquid. To conduct a test to EN ISO 20344:2011 clause 8.6.2, a 25mm x 150mm test specimen is cut from the outsole and reduced in thickness to 3mm. After immersion in the test liquid at 23°C for 22 hours and with excess surface liquid removed, the test piece is assessed using a Ross flexing machine at a temperature of -5°C. The SATRA STM 141F (a 12-station, low temperature Ross flexing machine shown in figure 4) can be used for this test. The tests should be carried out in accordance with Annex C of ISO 4643:1992. The requirement for this test is that after 150,000 cycles the cut growth in the test piece should be no more than 6mm. Footwear which meets the requirements of this test can be marked with the symbol ‘FO’.
This now completes the series of articles looking at the application of SATRA test equipment to the requirements set out in EN ISO 20345:2011 and the associated test methods set out in EN ISO 20344:2011.
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This article was originally published on page 42 of the December 2018 issue of SATRA Bulletin.