The Balance Between TPP & THL for Firefighter Turnout Gear Performance
TenCate Protective Fabrics makes sure that firefighter safety and comfort never take a back seat.
Thermal Protective Performance (TPP) and Total Heat Loss (THL) are both important performance factors to consider when selecting your turn out gear components.
Unfortunately, TPP and THL have an inverse relationship.
Typically, there has to be a tradeoff in one to improve performance in the other. You can’t have maximum TPP and also have maximum THL.
You have to choose the balance of TPP and THL that is right for you, and select your components, especially the thermal barrier, accordingly.
TPP or Thermal Protective Performance
The TPP test measures the thermal insulation of the composite: outer shell, moisture barrier, and thermal barrier. The test, which uses a thermal exposure representative of flashover conditions, measures the amount of time it takes for enough heat to pass through the composite to cause a second degree burn.
TPP is a harsh test. It is intended to ensure that fire fighters who may be caught in such a situation have a few seconds to escape. Fire fighters are not intended to work in these conditions. Protection is measured in seconds, and conditions encountered in the field may be even more severe than the test.
Thermal Protective Performance is primarily a function of the thermal barrier, which provides the majority of the thermal insulation. In general, thicker needle punch batt thermal barriers provide higher TPP, and thinner spunlace batt thermal barriers provide lower TPP. Unfortunately, thermal barriers that provide higher TPP tend to provide lower THL. If you want to adjust your TPP, focus on the thermal barrier.
THL or Total Heat Loss
Total Heat Loss (THL) measures the ability of the composite (outer shell, moisture barrier, and thermal barrier) to allow heat and moisture vapor to escape from the wearer through the garment. This is an important factor in reducing heat stress.
THL is driven primarily by the moisture barrier, but the thermal barrier also has significant impact. Thin spunlace batt thermal barriers typically provide better THL results, while thicker thermal barriers tend to offer lower THL performance. Thermal barriers that provide higher THL usually provide lower TPP.
It is also important to note that it typically takes at least a 20 to 25 point difference in THL to be noticeable by fire fighters in the field, depending on the conditions present and the individual.
TPP and THL test results have some inherent variability. In recognition of this variability, the respective NFPA test methods require that each TPP and THL test consist of three specimens. The TPP and THL ratings are based on the average of the three specimens. In addition, 8 percent variance is allowed between the individual specimen results and the average result in TPP tests, and 10 percent variance is allowed in THL tests.
TPP and THL are important performance factors and certainly should be considered when selecting your components, but understand there is variance in test results and consider ratings in ranges.