What is the ASTM F2700 Heat Transfer Performance (HTP) Test for FRC?
When the 2012 edition of the NFPA 2112 standard was published, a number of changes were made to clarify certain areas, add information in areas not previously covered, and keep some terminology to be consistent with NFPA 2113. NFPA 2112 essentially evaluates protective performance of FR garments in flash fires, while its sister standard NFPA 2113 outlines specification, care and use of garments.
With the update of NFPA 2112 from the 2007 version to the 2012 version, one of the most important updates was that the testing method was changed from the ASTM D4108-87 Thermal Protective Performance (TPP) test method to the ASTM F2700 Heat Transfer Performance (HTP) test method. (1)
What did TPP specify?
ASTM D4108-87 Thermal Protective Performance (TPP) test measured the amount of thermal protection a fabric would give a wearer in the event of a flash fire. The TPP is defined as the energy required to cause the onset of second-degree burn when a person is wearing the fabric. The higher the TPP, the more protective the fabric. The passing criteria for NFPA 2112 – 2007 Edition was a minimum TPP of six calories in a spaced configuration, and a minimum TPP of three calories in the contact configuration. (2)
TPP was first utilized in the 1980s as a method to evaluate the effectiveness of fire fighter turnout gear. When the ASTM F23 Committee on Protective Apparel reviewed this test method in the mid-2000’s, the Committee determined that TPP did a poor job of measuring the heat a fabric would block to prevent a burn – the protective part of TPP. As such, the Committee created HTP (Heat Transfer Performance) where part of the transition from Thermal Protective Performance (TPP) was to remove all references to protection.
What is HTP?
ASTM F2700 is the Standard Test Method for Unsteady-State Heat Transfer Evaluation of Flame Resistant Materials for Clothing with Continuous Heating. This test method is intended for the determination of the heat transfer performance (HTP) value of a material, a combination of materials, or a comparison of different materials used in flame resistant clothing for workers exposed to combined convective and radiant thermal hazards.
This test method evaluates a material’s unsteady-state heat transfer properties when exposed to a continuous and constant heat source. In the test method, a swatch of fabric is positioned horizontally and exposed to a two cal/second flame. A sensor measures the amount of energy that passes through the fabric during the exposure. Once sufficient heat has passed through the fabric to cause 2nd degree burn, the flame exposure is terminated. The difference between the amount of energy the fabric is exposed to, and the amount of energy that passes through the fabric during the exposure, is essentially that fabric’s HTP. (3)
This video by Waxman Fibres shows the ASTM F2700 HTP Test on Protal 5 fabric:
It’s important to note that this test method does not predict skin burn injury from the heat exposure, as it does not account for the thermal energy contained in the fabric specimen after the test. Because fabric can store heat that can transfer onto a worker’s body after the exposure to flame ceases, it is quite possible that a worker could be burned when exposed to hazard equal to his/her FRC’s HTP; this issue is addressed by ASTM F2703.
ASTM F2703 is the Standard Test Method for Unsteady-State Heat Transfer Evaluation of Flame Resistant Materials for Clothing with Burn Injury Prediction. This test is extremely similar to ASTM F2700 except it uses an iterative approach to predict the onset of burn, including any impact from heat stored in the fabric after the exposure to flame has ceased.
Mirroring the test in ASTM F2700, ASTM F2703 exposes the fabric until burn is predicted. In ASTM F2703, the sensor continues to record for at least another 30 seconds capturing the impact of heat that is stored in the fabric. Then a second test is performed with a shorter exposure to determine if burn would occur within approximately 30 seconds after the end of the flame exposure. If burn occurs, another test is performed and the exposure is further shortened. If no burn occurs, then another test is run at a time halfway between the exposure of the first and second tests. This continues until the exposure is within 0.5 cal of predicted burn, which is the fabric’s Thermal Performance Estimate (TPE). (4)
Higher values of Thermal Performance Estimate ratings determined in this test associate to higher values of thermal (convective and radiative) energy protection against a predicted skin burn injury. The HTP method is considered a more uniform and consistent method to measure the impact on the wearer than was TPP. (1)
ASTM F2700 or ASTM F1930?
Contrary to ASTM F1930, which is extremely complex and requires a high degree of technical expertise in both the test set-up and operation, the ASTM F2700 HTP test is smaller in scale and less expensive to conduct. HTP can be conducted on fabric to assure it doesn’t change but this test does not account for the impact of thermal garment shrinkage on predicted injury.
It’s important to note that the ASTM F2700 test standard is used to measure and describe the response of materials, products, or assemblies to heat under controlled conditions, but does not by itself incorporate all factors required for fire hazard or fire risk assessment of materials, products or assemblies under actual fire conditions.
This is why NFPA 2112-2012 specifies both ASTM F2700 and ASTM F1930.
References for this post were accessed February 2014: