Classification of metabolic and respiratory demands in fire fighting activity with extreme workloads

Abstract

Fire fighting work comprises work tasks requiring an energy yield at maximal or close to maximal levels of the individual. Due to the very nature of fire fighting more complex physiological variables are difficult to measure. We measured metabolic and respiratory responses in 15 male, professional fire fighters during simulated work tasks on a test ground. Work time was on the average 22 min with individual components of work tasks lasting 2–4 min. The mean oxygen consumption for the whole exercise (22 min) was 2.75±0.29 l/min. The most demanding work task demanded an oxygen uptake of 3.55±0.27 l/min. Corresponding values for respiratory minute volumes were 82±14 and 102±14 l/min, respectively. Heart rates averaged 168±12 for the whole test and 179±13 beats/min for the heaviest work task. Two new classes for classification of intensive and exhausting, short term physical work are proposed for inclusion in ISO8996 and values for relevant parameters are proposed.

Introduction

Fire fighting comprises hard physical work in combination with external physical stress such as heat and chemical hazards. The physical demands on fire fighters are high in terms of energetic and muscular capacity (Danielsson et al., 1998; Gledhill and Jamnik, 1992a; Kilbom, 1980; Romet and Frim, 1987). Realistic exercise tests are administered to fire fighters at regular intervals in order to maintain skills and physical fitness (Ben-Ezra and Verstraete, 1988; Gledhill and Jamnik, 1992b; O’Connell et al., 1986; Oldham et al., 2000; Schonfeld et al., 1990; Smith et al., 2001). In addition, physical training is encouraged and often allowed during work hours. Knowledge of the metabolic requirements during realistic fire fighting exercises is of great value for operational planning and for designing and selecting appropriate personal protective equipment. Fire fighting is a world-wide type of activity and there is a need for classification of the work in terms of metabolic and respiratory requirements. This kind of work is not readily covered in the classification scheme of metabolic rate provided in ISO 8996 (2004).

Owing to the nature of work and the use of personal protective equipment more complex physiological measurements are difficult or even impossible to undertake. In real fire fighting work the high heart rates may contain a considerable portion of psychological stress (Fatollahzadeh, 1997; Sothmann et al., 1992). However, a number of studies using heart-rate monitoring during simulated fire fighting exercises with limited psychological stress levels indicate that individuals easily reach near maximal and even maximal values of heart rate (Barnard and Duncan, 1975; Bennett et al., 1995; Danielsson and Leray, 2000; Louhevaara et al., 1995; Manning and Griggs, 1983; Romet and Frim, 1987; Smith et al., 2001). Estimations of the energetic requirements are based on heart rate responses (Bilzon et al., 2001; Serra et al., 1998; Sothmann et al., 1991) or ventilation (Danielsson and Leray, 2000). Recently, direct measurements of oxygen uptake and metabolic rate have been reported (Bergh and Danielsson, 1998; Danielsson et al., 1998; Holmér et al., 1997; Serra et al., 1998). Depending on type of activity they are in the range 1.5–4.3 l/min. Metabolic rate was reported at 1400 W for subjects carrying a victim upstairs (Danielsson et al., 1998).

Respiratory responses have been studied using measurement of air consumption from the compressed air apparatus. The mean value for the whole exercise period (about 20–25 min) was reported at 54 l/min (Lusa et al., 1993). A few dynamic measurements of respiratory responses have been reported and indicate minute ventilation values of more than 100 l/min during short periods of work. The average for a 20–25 min fire fighting drill was reported at 82 l/min (Holmér et al., 1997). Knowledge about required air volumes and minute ventilations are required for the establishment of requirements on respiratory protective equipment. Recent studies have indicated that peak inspiratory flow rates are 3–4 times higher than the minute volume (Berndtsson, 2004). Flow rates of 3–400 l/min through filters and breathing masks are much higher than the flow rates currently used for testing filters and masks.

This paper reports the energetic and respiratory responses of fire fighters to a simulated fire fighting exercise in a training house. Furthermore, it analyses energetic and respiratory demands associated with exhaustive fire fighting work and proposes values for classification of work.