Ebola: Improving the Design of Protective Clothing for Emergency Workers Allows Them to Better Cope with Heat Stress and Help to Contain the Epidemic

Abstract

It is a complex task to find optimal protective clothing to prevent the spread of Ebola virus disease (Martin-Moreno et al., 2014; Ryschon, 2014). The fear of getting infected is an obstacle for recruiting healthcare workers. In addition, the current design of protective clothing might curtail their working capacity severely in the hot and humid climate of West Africa and, in addition, paradoxically increase the risk of infection. Emergency work in full protective clothing including respiratory mask may lead to extreme heat stress in the hot climates resulting in shortened work time, dehydration, reduced professional judgement, and exhaustion. This increases risk of infection of health stuff (WHO, 2014). In Monrovia, Liberia, daytime maximum temperatures in the end of the year often reach 30–31°C, and the temperatures will be higher January to May, the hot season (Kjellstrom et al., 2014; http://climatechip.org/). In order to manage this heat stress, the workers need breaks (Kjellstrom et al., 2009). This leads to a frequent need to remove the protective gear, which involves an increased risk of infection. The multiple steps to remove the suit can take up to 30min (Kitamura, 2014). The modified Predicted Heat Strain (ISO 7933, 2004) model was used to indicate the expected work times (Fig. 1). The estimation was made based on the following assumptions. Standard man was chosen for the model calculations. Medium heavy activity (300W) was taken as the average work rate. The core temperature limit to cease such emergency work was set to 38.5°C. Three clothing types with different moisture permeability (im) were selected for comparison: an impermeable outer layer (im = 0.00), a semipermeable outer layer (im = 0.07), and a relatively tight but still permeable outer layer (im = 0.20). The basic clothing insulation in all cases was theoretically taken as 1 clo (0.155 m2K W−1) for comparative purposes. In all air temperature conditions, the other environmental factors were kept constant. Ambient water vapour pressure was set to 3.0 kPa, air velocity/body motion was 1 m s−1, and there was assumed no radiation effect present (work indoors or in shade). Continuous work times for a work rate of 300W at different air temperatures before reaching a core temperature limit at 38.5°C in clothing with different moisture permeability (im). The chosen work load in impermeable and semipermeable clothing allows 40min or shorter exposure during the hottest periods (Fig. 1) until the core temperature exceeds the suggested safe limit for occupational exposure. Higher core temperature is associated with decreased mental performance and increased misjudgement and mistakes (O’Neal and Bishop, 2010). Maximizing the moisture permeability and minimizing the clothing layers worn beneath the protective gear, provided that it should be resistant to penetration by body fluids, is a simple way of preventing heat stress and increasing the time spent inside the gear. However, dehydration and water intake must also be considered during extended exposures. A heat stress management program including rehydration should be an essential part of the overall health and safety program in any case. A desirable addition would be personal cooling used inside the protective clothing, such as cooling vests with ice or phase change materials (PCMs; Gao, 2014) or filtered ventilated coveralls (Kuklane et al., 2012). This may prolong working time to about 2h and reduce the number of gear changes per day. With 2-h work time in protective gear, the number of required personnel could be halved with possible decrease in contaminated waste. The final choice of the cooling method depends on specific air temperature and humidity. Increasing air temperature and, especially, humidity do reduce the effectiveness of air cooling and increase the benefits of PCM products. The use of PCMs requires freezers or cool areas for solidification after use. Cooling vests with ice are the cheapest and electricity for freezers is required. Power is one of the basic resources to provide healthcare and to cope with epidemics. Otherwise, the other types of PCM, e.g. Glauber’s salt or organic hydrocarbons/wax, with melting/solidifying temperature at about 28°C are available. For workers’ recovery after heat exposure, a room with air temperature below 27°C is recommended. The room or connected facilities could be used for PCM solidification storage. If still unavailable, then the melted PCM can be solidified in a relatively cooler water bath (using underground/well water, etc.), in an underground cave or in a cooler area during night. The higher the melting temperatures are, the less effective cooling is. However, if the temperature gradient is about 6°C or greater, the PCM can still provide a cooling effect. Considering cooling effect in ventilated garments, the provided air flow should be above 100 l min−1. There are filtered fan systems available on the market that manage the flows up to