Nina L. Turner

Effect of Boot Weight and Sole Flexibility on Gait and Physiological Responses of Firefighters in Stepping Over Obstacles

Objective: The authors investigated the effect of boot weight and sole flexibility on spatiotemporal gait characteristics and physiological responses of firefighters in negotiating obstacles. Background: Falls and overexertion are the leading causes of fire ground injuries and fatalities among firefighters. There have been few in-depth studies conducted to evaluate the risk factors of falls and overexertion associated with firefighter boots. Method: For the study, 13 female and 14 male firefighters, while wearing full turnout clothing and randomly assigned boots, walked for 5 min while stepping over obstacles. The independent variables included boot weight, sole flexibility, gender, and task duration. Spatiotemporal measures of foot trajectories and toe clearance were determined. Minute ventilation, oxygen consumption, carbon dioxide production, and heart rate were measured. Results: Increased boot weight was found to significantly reduce trailing toe clearance when crossing the 30-cm obstacle. Significant increases in lateral displacement of the foot were found near the end of the 5-min walk compared with the beginning of the task. Increased boot weight significantly increased oxygen consumption. There were significant decreases in oxygen consumption for more flexible soles. Conclusion: Firefighters were more likely to trip over obstacles when wearing heavier boots and after walking for a period of time. Boot weight affected metabolic variables (5% to 11% increases per 1-kg increase in boot weight), which were mitigated by sole flexibility (5% to 7% decrease for more flexible soles). Application: This study provides useful information for firefighters and boot manufacturers in boot selection and design for reducing falls and overexertion.

Physiological Effects of Boot Weight and Design on Men and Women Firefighters

The purpose of this study was to determine the effects of two leather (L1, L2) and two rubber (R1, R2) boots on firefighters’ metabolic and respiratory variables during simulated firefighting tasks. Twenty-five men and 25 women, while wearing full turnout clothing, a 10.5-kg backpack, gloves, helmet, and one of four randomly assigned pairs of firefighter boots, walked for 6 min at 3 mph (4.8 km/hr) on a level treadmill while carrying a 9.5-kg hose and climbed a stair ergometer for 6 min at 45 steps per min without the hose. Minute ventilation ( E), absolute and relative oxygen consumption ( and ml.kg.min-1, respectively), CO2 production (), heart rate (HR), and peak inspiratory (PIF) and expiratory (PEF) flow rates were measured, and an average of the breath-by-breath data from minute 6 was used for analysis. During treadmill exercise, a 1-kg increase in boot weight caused significant (p < 0.05) increases in E (9%), (5 – 6%), (8%), and HR (6%) for men, whereas a 1-kg increase caused significant increases in (3 – 4.5%) and (4%) for women. During stair ergometry, a 1-kg increase in boot weight caused significant increases in E(~3%), relative (~2%), (3%), and PIF (~4%) in men and women (p < 0.05) and a significant increase in absolute (~3.5%) in men only. Mean increases in metabolic and respiratory variables per 1-kg increase in boot weight were in the 5 to 12% range observed previously for men during treadmill walking but were considerably smaller for women. Mean increases in oxygen consumption during stair ergometry were statistically significant but were smaller in the current study than previously observed and may not be practically significant. There was no significant effect of boot design in addition to boot weight for either mode of exercise.

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 persons 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 ≤ 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 ≤ 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.

Impact of Harness Fit on Suspension Tolerance

Objective: This study investigated the effect of body size and shape and harness fit on suspension tolerance time. Background: Fall victims may develop suspension trauma, a potentially fatal reduction of return blood flow from legs to the heart and brain, after a successfully arrested fall if they are not rescued quickly or the harness does not fit them well. Method: For this study, 20 men and 17 women with construction experience were suspended from the dorsal D-ring of a full-body fall-arrest harness. Their suspension tolerance time, physical characteristics, and harness fit levels were assessed. Results: Body characteristics (i.e., weight, stature, upper- and lower-torso depths) were associated with decreased suspension tolerance time (r = –.36 ~ –.45, p ≤ .03). In addition, harness fit affected suspension tolerance time; workers with a torso angle of suspension greater than 35°, a thigh strap angle greater than 50°, or a poorly fitting harness size had shorter suspension tolerance time (mean differences = 14, 11, and 9.8 min, respectively, p ≤ .05). Conclusion: Body size and harness fit were predictors of suspension tolerance time. Selecting well-fit harnesses and establishing a 9-min rescue plan are suggested to ensure that no more than 5% of workers would experience suspension trauma. Applications: The study provides a basis for harness designers, standards writers, and manufacturers to improve harness configurations and testing requirements for better worker protection against suspension trauma.

The effect of dry and humid hot air inhalation on expired relative humidity during exercise

It has been previously demonstrated that under certain environmental conditions, expired air is not fully water saturated because of the low relative humidity of the first part of the expirate. This finding is of interest to those involved in respirator research, particularly those who design and test robotic metabolic simulators. These simulators must accurately mimic the physiological responses of human airways to breathing air of various temperatures and relative humidities (RHs). Because these responses are not fully quantified, this study examined the mean relative humidity of expired air during four inspired air conditions: cool dry (26 degrees C, 60% RH), cool humid (26 degrees C, 95% RH), hot dry (45 degrees C, 11% RH), and hot humid (45 degrees C, 95% RH). These conditions were administered during three exercise intensities: rest, low (35% VO2max), and moderate (70% VO2max). As compared to the cool dry (CD) condition, frequency of breathing (f) was 9.3% lower and tidal volume (VT) was 9.4% greater across all exercise intensities for the hot humid (HH) condition (p less than 0.05). Mean expired relative humidity (ERH) was substantially lower for the hot dry (HD) condition as compared to the other three conditions during each sampling period. These findings support the conclusion that the mean ERH of expired air depends upon several respiratory and environmental factors in addition to inspired air temperature.

Physiological Evaluation of Air-Fed Ensembles

The goal of this study was to evaluate the respiratory and metabolic stresses of air-fed ensembles used by workers in the nuclear, chemical, and pharmaceutical industries during rest, low-, and moderate-intensity treadmill exercise. Fourteen men and six women wore two different air-fed ensembles (AFE-1 and AFE-2) and one two-piece supplied-air respirator (SA) at rest (REST) and while walking for 6min at oxygen consumption (V.O2) rates of 1.0 (LOW) and 2.0 l min(-1) (MOD). Inhaled CO2 (FICO2), inhaled O2 (FIO2), pressure, and temperature were measured continuously breath-by-breath. For both LOW and MOD, FICO2 was significantly lower (P < 0.03) and FIO2 was significantly greater (P < 0.008) for SA compared with AFE-1 and AFE-2 in women, while in men, similar trends were observed. Significantly lower FICO2 (P < 0.009) and significantly greater FIO2 (P < 0.04) were consistently observed in AFE-1 compared with AFE-2 in men during LOW and MOD. For both men and women, average FICO2 exceeded 2.0% in AFE-2 during MOD. During LOW and MOD, average FIO2 in AFE-1 and AFE-2 dropped <19.5% in men and women. For men and women, average inhalation pressures (PIave) were significantly greater in both air-fed ensembles than SA (P < 0.001) during REST, LOW, and MOD. Inhaled gas temperature was significantly lower in SA than in either air-fed ensemble (P < 0.001). When the air supply was shut off during walking, the time taken for minimum FICO2 to reach 2.0% was <38 s for all three ensembles in both men and women, an observation that has implications for the design of emergency escape protocols for air-fed ensemble wearers. Results show that inhaled gas concentrations may reach physiologically stressful levels in air-fed ensembles during moderate-intensity treadmill walking.

Investigation of a heat stress-related death of a fire fighter

The National Institute for Occupational Safety and Health (NIOSH) Division of Surveillance, Hazard Evaluations and Field Studies (DSHEFS) conducts investigations of health hazards in the workplace under the NIOSH Health Hazard Evaluation (HHE) program. In September 1990, the International Association of Fire Fighters (IAFF) requested that NIOSH assess the health and safety practices used by fire personnel during a brush fire on September 6, 1990, in Sedgwick County, Kansas. A 25-year-old fire fighter died of heat stroke at the scene.The NIOSH site visit to Sedgwick County, Kansas included a tour of the fire scene, personal interviews with 25 fire fighters and support personnel, and a review of incident reports, incident command procedures and other documents. NIOSH investigators concluded that a preventable series of events preceded the fire fighters death. Recommendations were made for incident command and safety procedures, as well as medical monitoring, rehabilitation of fire fighters at fire scenes, and rehydration schedules.