Personal Protective Equipment (PPE) standards whether they are European EN or American NFPA, play a crucial role in ensuring the PPE meets minimum performance requirements. However, many users overlook the details contained within these standards, leading to potentially inadequate protection. It’s essential to understand that simply using terms like “certified” or “not certified” as a gateway for selection helps, but lack of proper understanding of the detail means workers may not be protected properly.
The Basic FR Standards
When it comes to flame and heat protection, EN 11612 is the European standard, while the US equivalent is NFPA 2112. Both describe performance requirements for clothing to protect against flame and heat, especially in the form of short duration flash fire. Both contain a range of testing to indicate the fabric and garment performance in different circumstances, in particular the performance of the fabric in resisting heat energy transfer. To understand the importance of this, it is first necessary to recognise two critical points; first, what actually causes burns, and second, that energy can transfer from the source to skin in different ways.
What Causes Burns?
Most people believe temperature is the damaging factor. It certainly plays a part, but the critical issue is the rate of change of temperature in the skin cells, not the temperature per se. Cells can manage a slow change to quite high temperatures without damage, but a rapid change in temperature, even at lower levels, will result in cell destruction, manifesting as skin burns. (If you doubt this, consider that frostbite is a skin burn at sub-zero temperature). The rate of temperature change in cells is related directly to the amount and rate of heat energy that transfers from the source to the garment-wearer’s skin. This is why arc flash is so dangerous – because it can involve huge amounts of heat energy produced in a very short time. Preventing damage in the form of burns therefore requires minimising the transfer rate of heat energy, and this is the purpose of FR clothing, to prevent and slow the rate at which heat energy reaches the wearers skin.
How Does Heat Energy Transfer?
There are three main routes by which energy transfers from the heat source to the skin:
- Radiant Heat: This occurs through electromagnetic radiation, similar to the warmth felt from a fire or sunlight.
- Convective Heat: This transfer happens through the movement of a medium, such as a gas or plasma from a flame.
- Contact Heat: This occurs through direct contact with hot surfaces.
EN 11612 provides for separate testing of the ability of garment fabric to resist heat energy transfer for each of these types, in each case placing a fabric sample between a relevant heat source and a calorimeter, and measuring the HTi (Heat Transfer Index) – the time taken to record a specific rise in temperature. Fabric is classified as 1 to 3, with 3 the highest (In the case of radiant heat energy, an additional class 4 is included specifically for aluminised garments designed for resistance of high temperatures and high levels of heat energy).
Detailed Testing in EN 11612
The EN 11612 standard includes five heat energy resistance tests:
- ISO 9195: Convective Heat Resistance (Code Letter B)
- ISO 6942: Radiant Heat Resistance (Code Letter C)
- ISO 12127: Contact Heat Resistance (Code Letter F)
- ISO 9185: Resistance to Molten Iron Splash (Code Letter D)
- ISO 9185: Resistance to Molten Aluminum Splash (Code letter E)
The final two assess the fabric’s ability to withstand contact with molten metals, relevant for industries such as welding and foundry work. These tests measure the ability of the fabric to allow molten metal to flow off rather than resist the heat energy itself. This is important because if molten metal remains on the fabric, the temperatures involved are such that heat resistance becomes irrelevant.
Classifications achieved are indicated on garment labeling and user instructions by the code letters B to F, along with the classification. So, for example, a garment labeled B2, F1 indicates testing to the convective and contact heat resistance tests with classes achieved of 2 and 1.
However, the requirements in the standard mean garments need not be tested to all five of these tests. The requirement is that at least a class 1 is achieved in at least one test. As a result, many cheaper options have only a single test, whereas better quality products often feature more testing, providing users with more detailed information about the garment protective capabilities.
NFPA 2112 also tests heat energy transfer resistance. A single test (ASTM F2700) places the fabric horizontally between the flame of a burner and a heat sensor, with both spaced and contact options. In this test, Heat Transfer Performance (HTP) is measured by calculating the difference between the heat energy (in calories) applied to the fabric and the heat that passes through it. The resulting HTP rating reflects the garment’s effectiveness, with minimum performance requirements for both spaced and contact settings.
The key point in both standards is the importance of understanding the specific details for proper garment selection. EN 11612 uses distinct tests and classifications to measure performance against various types of heat energy transfer, enabling users to choose garments that address the specific heat hazards in their application. A quick selection based solely on EN 11612 certification, without considering these detailed tests, could overlook critical factors—such as a contact heat hazard—leaving the wearer with a garment tested only for radiant heat resistance.
In ASTM 2112, understanding of the heat transfer HTP ratings in the spaced and contact settings can be important in understanding how this applies to your specific application and the heat hazards involved.
Conclusion
Whilst most users understand the need for ensuring PPE is at least certified to a standard to ensure a minimum performance, certification does not indicate protection in a specific application, and too few look into the detail within standards and the testing that certification entails and that can be important in selecting the right PPE for the task. There are many examples in many standards of this type of detail being critical to PPE selection.
In the case of FR clothing, the purpose is to prevent and delay transfer of heat energy to the skin of the wearer, and both European EN and North American NFPA standards include testing of heat transfer performance for specific types of heat energy transfer. A robust selection process for FR workwear should therefore include assessment of these test results to ensure garments chosen will keep workers safe from the specific heat hazards in your application.
