Garments to protect against heat and flame

A number of industries require workers to wear heat- and flame-resistant clothing. How can this be tested for its effectiveness?

Heat and flame garments provide protection against a huge variety of risks. EN ISO 11612:2015 – ‘Clothing to protect against heat and flame’ is the generic standard for heat and flame protective garments, which are split into three different categories of risk:

• ‘Level 1’ to indicate exposure to low risk
• ‘Level 2’ to indicate exposure to medium risk
• ‘Level 3’ to indicate exposure to high risk.

Limited flame spread is the common test regardless of risk, to at least ‘method A’ (face ignition). While this is a mandatory test for the materials involved, it is also key for hardware and fastening devices to ensure they are properly functional after exposure. Laboratory testing is just a simulation of potential real-world risks, but it does give a performance indication of whether components such as slide fasteners and touch and close fasteners will melt and fuse together, therefore rendering the wearer trapped in a flaming garment.

This testing also includes ‘method B’ (edge ignition), which is used to ensure that if flame impingement is on the hem of the garment, the flame does not spread inside and up the garment. This is especially important as the risk of ignition at the edge or hem is much higher than in the centre of the garment.

Shrinkage due to heat resistance can constrict the user, particularly in the case of permanently affixed additions such as retro-reflective tape. This is also the case with melting fastening devices, similar to the limited flame spread testing outlined above.

Heat transmission takes many forms, which is why it is so essential to choose the correct one for your garment’s intended end use. EN ISO 11612 has specific code letters for each property, as follows:

Code letter B – Convective heat. The material is exposed to a flame and the heat transfer is measured through the specimen. Due to the intense heat, the 40°C rise through the material is rapid – usually only taking several seconds for single layer testing.

Code letter C – Radiant heat. Using ‘method B’ of ISO 6942:2022 – ‘Protective clothing – Protection against heat and fire – Method of test: Evaluation of materials and material assemblies when exposed to a source of radiant heat’, the material properties are tested to resist heat transfer through radiation. The heat transfer for this method is via electromagnetic waves, and therefore is more readily influenced by the material’s surface finish, colour and reflectivity. These properties all work in conjunction to try to reflect the heat rather than absorb it. Radiant heat is the only test that can achieve Level 4. However, this is aimed at materials which have a metallised surface to reflect as much heat as possible.

Additionally, suppliers of the garment may claim protection against molten aluminium and/or molten iron splash (code letters ‘D’ and ‘E’ respectively). If either of these are claimed, additional design requirements need to be complied with. These additional requirements ensure that hot metal does not become entrapped within the garment, as hot material trapped in pockets and similar places can soon ignite or transfer their heat through the material and into the user.

Code letter F – Contact heat. As this test involves quite a large heated mass, there is a considerable amount of heat transfer directly into the material when the sample meets the heated cylinder, as well as pressure against the specimen. This is to simulate risks against contact heat (such as elbows encountering oven doors), or through oven gloves when picking up high-temperature items. The classifications differ between standards or products. Nevertheless, it is determined by a combination of time applied to reach a temperature rise of 15°C and the temperature of the heated cylinder.

As well as flammability and heat transfer performance, material testing of mechanical properties also needs to be carried out. This is to ensure that the main garment materials and constructional seams are adequate and will not break or burst during movement of the wearer.

Garments are required to undergo a ‘design assessment’ This is to check that their coverage is adequate and can be used in conjunction with other articles of PPE, such as balaclavas, gloves and footwear.

General requirements also need to be complied with, as outlined in ISO 13688:2013+A1:2021 – ‘Protective clothing – General requirements’. This includes ergonomic and innocuousness testing for the presence of azo dyes, chromium VI and nickel.

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