Volume 2, Issue 5 (May 2005)
Evaluating Thermal Protective Performance Testing
Even as better materials are developed for protective clothing, NFPA data indicate the number of burn related fire fighter deaths and severe injuries is increasing. These injuries are unexpected for the most part. As a result, questions arise about Thermal Protective Performance (TPP) ratings and whether performance changes are due to use or the effects of aging. As part of a NIST-sponsored Small Business Innovative Research project, current TPP test techniques were evaluated. Some changes and extensions are suggested.
In TPP tests, dry fabric samples or ensembles are exposed to heat flux of 83 kW/m2 with nominally 50% radiative and 50% convective heat transfer. Heat transmission through the test sample is measured with a copper calorimeter. The TPP Rating is the time in seconds required for a 2nd degree burn.
Current problems include:
1) Current test methods overestimate time to 2nd degree burn.
2) No information is provided on maximum potential burn damage.
3) No information is provided on heat transfer or fabric properties.
4) No information is provided on how performance changes with use.
Suggested changes and extensions include:
1) Change the heat source — use a modified radiant protective performance technique.
2) Replace the copper calorimeter with a thermal skin simulant sensor.
3) Estimate burn damage using a two step analysis method.
4) Obtain both dry and damp thermal properties for modeling clothing performance.