In our article “Primary & Secondary FR Workwear Differences & When to Use Each” we looked at the danger from inappropriate choice of garment to be worn over primary FR workwear. This article considers the methods available to determine if fireproof clothing – either primary or secondary – will provide protection against flames and heat.
Many safety managers face the need for workers to be protected from both flash fire and chemical hazards at the same time, or simply to keep FR workwear clean by wearing a disposable coverall over it. The previous article showed that incorrect choice of overgarments, specifically the use of standard disposable or chemical suits, creates a hazard, resulting in an increase of body burn that could be fatal.
So, when wearing secondary FR garments over primary FR clothing, how do you know you remain protected?
Do tests in FR clothing standards tell you how well fireproof clothing or layered system will protect?
Given that protection relates to the effectiveness in resisting transfer of heat energy from a source to the skin of the wearer (see previous article), the question is “do the tests indicate resistance to heat energy transfer?”.
The standards for FR clothing in both Europe (EN 11612) and North America (NFPA 2112) contain four types of tests: –
1. Resistance to Shrinkage.
EN 11612 and NFPA 2112 contain a test to ensure minimal shrinkage in response to heat. Details vary, but in both a fabric sample is placed in an oven and sample size before and after compared. The fabric must not shrink more than a specified percentage.
Do these tests indicate a level of protection?
No… but they are nevertheless important. A key element of protection is the insulating layer of air between the garment fabric and wearers’ skin. If a fabric shrinks it will tighten on the body, reducing that insulation and allowing more heat energy transfer. The last thing you need in FR workwear is a tight-fitting design!
2. Flame Resistance or Vertical Flammability Tests
These assess how effectively a fabric sample suspended vertically resists ignition, burning and melting. Again, details vary, but both apply a small flame to the sample for a specified time. The essential requirements are that the fabric must not continue to burn and must not drip molten or burning material.
Does this test indicate a level of protection?
No. It does, however, ensure that in contact with flame the fabric will not ignite and burn and therefor worsen injury. However, in answer to the question, “does it protect?”, it provides no information. In fact, a fabric that provides no heat resistance whatsoever could pass this test.
3. Heat Energy Resistance Tests.
These assess a fabric’s ability to resist transfer of heat energy so are critical in indicating the protective ability of the garment. In both EN and NFPA the principal is the same. A fabric sample is placed between a heat source and a heat calorimeter. The calorimeter measures how much heat energy transfers through the fabric by recording a rise in temperature.
There are differences in the two standards: –
- NFPA 2112 contains a single test to assess resistance of energy transfer in spaced and contact modes (reflecting fabric spaced and in contact with skin), and using a burner (for convective energy) and a heating element (for radiant energy).It calculates the “Heat Transfer Performance” (HTP); the energy filtered out by the fabric based on a 50% probability of a 2nd degree burn. An HTP mimimum of 3 cals/cm2 for contact, and 6 cals/cm2 for spaced, is required.
- EN 11612 contains five tests assessing resistance to different types of heat energy (convective, radiant, contact, and two tests for molten aluminium and iron).These (excluding the molten metal tests) measure the time until a specific rise in temperature in the calorimeter is reached. The results are classified at 1,2 or 3 with Class 3 the highest – being the longest time taken to achieve the temperature rise. (The radiant heat test has an additional Class 4 for high level radiant heat garments such as reflective aluminised clothing).
Do these tests indicate a level of protection?
Yes. The tests are designed to measure how effectively fabric will resist transfer of heat energy – the very purpose of FR clothing. The EN version may be more useful in practical terms with its classifications of different performance (which can be loosely associated with low, medium and high risk applications), whilst the NFPA version simply identifies a minimum performance requirement. However, in terms of providing an answer to the question “Does this garment protect?” they are limited as it can be difficult to relate the tests to real world applications.
On the other hand, perhaps their biggest shortcoming is they reflect performance of fire resistant clothing materials and not of garments. There is only one test type which assesses whole garments in the way they are used in the real world; the thermal mannequin test.
Heat Energy Transfer Types
There are different ways that energy can transfer from a heat source to the skin of a wearer: –
Convective: Energy transferred through a medium such as the plasma of a flame.
Radiant: Energy transferred via infra-red waves such as the energy radiated by the sun or an electric heat element.
Contact: Energy transferred through direct physical contact.
In assessing FR clothing, these different methods should be accounted for. Specific applications might require special consideration. For example, aluminised garments are specifically designed to use a shiny, polished surface to reflect high levels of heat energy, whilst heat resistance gloves should feature effective resistance to contact energy transfer.
4. Thermal Mannequin or “Flash Fire” Tests
Both NFPA and EN standards reference a thermal mannequin test. However, in NFPA the test is mandatory and specifies minimum performance, whilst in EN it is optional and defines no performance requirements.
The basics in both standards are the same: –
- A mannequin is covered in 123 sensors, each of which absorbs heat energy at the same rate as skin.
- Each heat sensor is connected to a computer which measures the heat energy absorbed, and using Stoll Analysis can predict (with a 50% probability) burn injury
- The test garment is put on the mannequin, and a flash fire event is simulated using burners positioned around the test rig. The burns are at a defined energy level and for a specific time (normally 3 or 4 seconds). The video below shows a thermal mannequin test on Lakeland’s Arc-X Arc Flash Rainwear garment [LINK].
The thermal mannequin test produces a prediction of likely body burn and can indicate areas of pain, 1st, 2nd and 3rd degree burn, represented visually by a map of the body, indicating where a burn is predicted, and using different colours for different depth of burn.
An example is shown here.
Each area represents one heat sensor on the mannequin. Orange areas represent 2nd degree burns, and red areas 3rd.
The shows a total body burn percentage of 53%.
Do these tests indicate a level of protection?
Yes. Of all the tests in the FR clothing standards, thermal mannequin testing is the only one that: –
- Tests whole garments
- Simulates a real-world flash fire scenario
- Tests garments in the way they are used in the real world
Most importantly, the flash fire test provides a unique method to compare performance of different garments and it is lamentable that it is only optional in EN 11612; many cheaper garments are not subjected to it. It is also the only effective method for assessing layered FR systems – such as wearing chemical protective clothing over primary FR workwear. In fact, this test is the only way to confirm the real consequences of wearing any garment over your thermal protective clothing.
A New Secondary FR Workwear Standard
In the USA the American National Standards Institute published ANSI 203 , a standard specifically for secondary FR workwear, in 2018. It requires comparative flash fire testing of primary FR workwear with and without overgarments to prove that the result is not a substantial increase in body burn. Given the uncertainty around wearing clothing over primary FR garments, even if users worldwide do not require certification to this new American standard, it would be an important step forward for global safety if its principle was applied and thermal mannequin testing of layered systems became the norm.
Conclusion: FR Standards tests are useful – but only one test is helpful in assessing layered Primary and Secondary FR Clothing Systems.
- Whilst the heat shrinkage resistance and vertical flammability tests provide important information about FR properties, they do not tell you if a garment will protect
- The heat energy resistance tests do provide important information on the fabric ability to resist heat energy transfer, but they test only fabrics and are challenging to apply to the real world
- Only the thermal mannequin tests assess whole garments in a simulated real-world, flash fire scenario and are suitable for indicating how effectively primary FR workwear alone will protect, and the effect of wearing a secondary layer over it.
Our free downloadable whitepaper includes a detailed summary and comparison of FR garment standards NFPA 2112 and EN 11612, including test descriptions, along with an outline of the new standard ANSI 203 – the first standard specifically developed for assessment of Secondary FR workwear.
What Secondary FR Clothing options are available and how do they perform in Flash Fire Testing?
In the previous article we saw the proof that wearing standard disposable coveralls over primary FR clothing is a hazard. In testing, predicted body burn increased from 37% to 53%, as well as adding more critical 3rd degree burns.
There are, however, several options that might be classed as “secondary FR clothing” – that is suitable for wearing over your primary FR clothing. Flash Fire testing provides the perfect method for clearly establishing how each performs.