Firefighters are routinely exposed to radiant heat in the course of their fireground activities. In some cases, firefighters have reported burn injuries under clothing where there is no evidence of damage to the exterior or interior layers of the firefighter protective clothing. Low levels of transmitted radiant energy alone or a combination of the transmitted radiant energy and stored energy released through compression can be sufficient to cause these types of injuries. This test method was designed to measure both the transmitted and stored energy in firefighter protective clothing material systems under a specific set of laboratory exposure conditions.

The intensity of radiant heat exposure used in this test method was chosen to be an approximate midpoint representative of ordinary fireground conditions as defined for structural firefighting (1), (2) . The specific radiant heat exposure was selected at 8.5 ± 0.5 kW/m² (0.20 ± 0.012 cal/cm²-s) since this level of radiant heat can be maintained by the test equipment and produces little or no damage to most NFPA 1971 compliant protective clothing systems.

5.2.1 Discussion-Utech defined ordinary fireground conditions as having air temperatures ranging from 60 to 300°C and having heat flux values ranging from 2.1 to 21.0 kW/m² (0.05 to 0.5 cal/cm²-s).

Protective clothing systems include the materials used in the composite structure. These include the outer shell, moisture barrier, and thermal barrier. It is possible they will also include other materials used on firefighter protective clothing such as reinforcement layers, seams, pockets, flaps, hook and loop, straps, or reflective trim.

The transmission and storage of heat energy in firefighter protective clothing is affected by several factors. These include the effects of "wear" and "use" conditions of the protective clothing system. In this test method, conditioning procedures are provided for the laundering of composite samples prior to testing, and also composite sample moisture preconditioning. The amount of moisture added during preconditioning typically falls into a worst case amount in terms of predicted heat transfer, as suggested by Barker (3).

Two different procedures for conducting the test are provided in this test method. Procedure A involves an iterative approach to determine the minimum exposure time followed by a fixed 60-second compression time required to predict a second degree burn injury. In this approach, the length of the radiant exposure is varied systematically using a series of tests to determine the length of the radiant exposure that will result in the prediction of a second degree burn injury. Procedure B involves using a fixed radiant heat exposure time to determine if a second degree burn injury will or will not be predicted. If a second degree burn injury is predicted, the time to a second degree burn injury is reported. If a second degree burn injury is not predicted, the result is indicated as "no predicted burn." Procedure B involves a fewer number of tests. This procedure includes recommended fixed radiant exposure times.