Protection from Heat and Flame
While it is possible to have intense heat without fire and vice versa, generally the two go hand-in-hand. Fabrics which offer suitable protection exclusively for one often do not offer protection for the other.
Heat Barrier Rating
Protection from heat relates to two factors; the type of fabric used to provide the protection and the weight and thickness of the fabric. It is generally conceded that a fabric that is light in weight will not be able to provide adequate insulation against heat; however the amount of protection given can vary quite considerably within the same weight range, depending on the composition of the fabric.
Thermal Protective Performance (TPP)
The Thermal Protective Performance (TPP) test is used for determining the thermal properties of the fabric being tested. The TPP is recognised in the NFPA 1971 and the ASTM F1060-08 as an acceptable measure of a fabric's protection when considering the amount of radiant heat a fabric can withstand. The TPP test is performed by having a convective/radiant heat source, or a combination of the two, with a heat flux of 2 cal/cm2 (calories per centimetre squared) impinged on the outer surface of a 4" by 4" area of the fabric. The heat is applied for a specific amount of time in order to reach the equivalent of a second-degree burn at the calorimeter on the other side of the fabric. The time (in seconds), which is multiplied by the heat flux of the exposure, gives the Thermal Protective Performance rating of the system. This constitutes the fabric's TPP.
Flame Barrier Rating
A fabric flame barrier must demonstrate that it will not support or promote flame when exposed to an ignition source. It is also essential that the fabric does not melt, drip or break-open when exposed to flame, rendering itself ineffectual as a barrier, thereby causing damage to underlying skin.
Flammability tests on fabrics may differ slightly, but commonly they involve the fabric being exposed to an open flame for a pre-determined period. At the end of the exposure time the damage to the fabric is assessed and a flame barrier rating allocated to it.
Molten Metal Splash Rating
The splash risk from molten metal is a major factor in the performance of protective fabrics.
Fabrics are rated on:
-
The speed with which they can shed molten metal, thus reducing the exposure risk to the heat of the metal.
-
The ability to provide burn protection to the underlying skin as the molten metal is being shed.
-
Their resistance to ignition through exposure to the heat generated by the molten metal.
Shedding of Molten Metal
Molten metals require careful evaluation to ensure the correct option is taken regarding protection. Different metals have different characteristics and will adhere to many fabrics.
Molten metal splash shedding tests utilise the relevant metal for the industry the fabric is intended for use in. The fabric being tested is laid over a layer of simulated skin and these are then set at an angle to allow shedding to occur. The results of the test pours are reported as the Molten Metal Splash Index (MMSI), calculated as the mean of the lowest mass poured to cause damage and the highest mass poured (of the 4 tests required) not causing damage.