A Comparison of Heat Accumulaton in the M3A2 and M3A3 Bradley Fighting Vehicles

Field data suggested that the Bradley M2M3 fighting vehicle A3 upgrade subjected the crew to greater heat stress than the previous System did. A study was conducted to determine if the Bradley A3 crew stations were hotter than those of the A2 and if so, what the operational implications were for crew performance. A Bradley A2 and A3 were place side by side in an environmental chamber and exposed to 30 deg, 40 deg, 80 deg, 100 deg, and 125 deg F with the hull fans off to 80 deg and 100 deg F with the hull fans on and to 80 deg F with one hull fan on. In addition, the vehicles were exposed to a 10-hour segment of the standard basic hot environmental scenario, with hull fans on and off Finally, the vehicles were run through a series of brief excursions to evaluate engine temperatures. During all testing, temperature data were collected at the drivers station, turret, and squad area at head, hand, and foot heights. Additional sensors recorded relative humidity, pressure, and additional temperatures in the vehicle. Smoke candles were used to evaluate air movement through the vehicles during a side test. Results showed that temperatures were consistently higher between 10 deg and 35 deg F in the A3 drivers compartment than in the A2 when the vehicles hull fans were off. Based on the smoke test, this appears to be caused by the turret fan creating an under-pressure that draws air into the drivers area from the engine. With the hull fans on, the A3 drivers compartment is between 2 deg F warmer and 4 deg F cooler than the A2. The A3 turret is still 5 deg to 8 deg warmer. This difference was not operationally significant. At 80 deg F, both the A2 and A3 were within acceptable limits. At 100 deg F, both vehicles exceeded recommended heat limits 85 deg F wet bulb globe temperatures WBGT. In the A2, the worst limiting locations were driver head and driver hand, with a maximum exposure of 1 hour.