Suspension tolerance in a full-body safety harness, and a prototype harness accessory

Workers wearing full-body safety harnesses are at risk for suspension trauma if they are not rescued in 5 to 30 min after a successfully arrested fall. Suspension trauma, which may be fatal, occurs when a person's legs are immobile in a vertical posture, leading to the pooling of blood in the legs, pelvis, and abdomen, and the reduction of return blood flow to the heart and brain. To measure suspension tolerance time, 22 men and 18 women with construction experience were suspended from the chest D-ring (CHEST) and back D-ring (BACK) of full-body, fall-arrest harnesses. Fifteen men and 13 women from the original group of subjects were then suspended using a newly developed National Institute for Occupational Safety and Health harness accessory (ACCESS), which supports the upper legs. Midthigh circumference changes were 1.4 and 1.9 cm, changes in minute ventilation were 1.2 and 1.5 L/min, changes in heart rate (HR) were 15.1 and 21.6 bpm, and changes in mean arterial pressure were 5.1 and -2.6 mmHg (p < or = 0.05) for all subjects during CHEST and BACK, respectively. Kaplan-Meier median suspension time for all subjects for the CHEST condition was 29 min (range 4-60 min) and 31 min (range 5-56 min) for the BACK condition. The 95th percentile for suspension time was 7 min for CHEST and 11 min for BACK. Cox regression revealed that body weight had a statistically significant effect on the time until experiencing a medical end point (p < or = 0.05) during the BACK condition. Mean (+/- SD) suspension time was 58 +/- 6 min (range 39-60 min) for all subjects for the ACCESS condition. There were no terminations due to medical symptoms during the ACCESS suspension, changes in physiological variables were small, and 85% of ACCESS subjects completed 60-min suspensions. These data provide information on motionless suspension tolerance time to standards-setting organizations and demonstrate the potential of a prototype harness accessory to delay or prevent suspension trauma.