The effects of protective clothing on metabolic rate

There are many industrial sectors where workers are required to wear personal protective clothing and equipment (PPC/PPE). Although this PPC may provide protection from the primary hazard, for example heat or chemicals, it can also create ergonomic problems. The growing concern regarding health and safety of workers has generated regulations and standards, as well as research and development in the area of PPC/PPE (1). Although these have helped to improve the quality of the PPC and increase the safety of the workers, information on the effect of the clothing on the wearer and the interactions between PPC, wearer and environment are limited. Most PPC is designed for optimal protection against the hazard present, however the protection in itself can be a hazard. There are important side effects to protective clothing and typically with increasing protection requirements, the ergonomic problems increase. The problems of protective clothing can be split into thermal and metabolic issues. By creating a barrier between the wearer and the environment, clothing interferes with the process of thermoregulation, particularly reducing dry heat loss and sweat evaporation. Protective clothing also increases the metabolic cost of performing a task by adding weight and by otherwise restricting movement. The binding or hobbling effect of bulky, stiff or multilayered clothing adds measurably to work (2) . Current heat and cold stress standards consider the balance of heat production and loss but focus on environmental conditions, clothing insulation and work rate metabolism. They also assume workers are wearing light, vapour permeable clothing. By failing to consider the metabolic effects of actual protective clothing, the standards can underestimate heat stress or overestimate cold stress; therefore current standards cannot be accurately applied to workers wearing PPC. The effects of protective clothing on workers has been studied across a number of industries but studies have emphasized the thermal effects of clothing, such as heart rate, core temperature responses to different garments and performance decrements in the heat. Very few studies have considered the metabolic effects. Multilayered clothing ensembles have been reported to increase oxygen uptake by an amount significantly in excess of that which can be accounted for by the increases in the clothed weight of the subjects. Teitlebaum and Goldman (1972) walked subjects on a treadmill either wearing an additional 5 layers of arctic clothing over their standard fatigues or carrying the 11.19kg weight of the five layers as a lead-filled belt. In conclusion, the authors suggest the significant increase on average of approximately 16% in the metabolic cost of working in the clothing compared to the belt can most probably be attributed to ‘friction drag’ between the layers and/or a ‘hobbling effect’ of the clothing (3). Duggan (1988) investigated the effect using a bench stepping task in military chemical protective clothing, with long underwear and quilted thermal jackets/trousers as extra layers. When corrected for clothing weight, VO2 was greater by an average of 9% (4). In order to obtain data on a wider range of PPC and further investigate this possible ‘hobbling effect’ an experiment was performed on an extensive set of protective clothing ensembles with a focus on the metabolic effects.