Personal protective equipment against infectious respiratory diseases

Abstract

The effectiveness of the personal protective equipment (PPE) is critical to prevent infection arising from severe acute respiratory syndrome, avian influenza A (H5N1) and other communicable respiratory infections. The objective of this research is to establish a sound scientific understanding of the protective performances and psycho-physiological roles of different types of respirators/masks or PPE ensembles in use, and identify how the design and fabric characteristics of the tested respirators/masks or PPE ensembles contribute to the protective efficiency and psycho-physiological well being. To reveal the knowledge gaps and ensure the originality of this study, a critical search of literature is reviewed in relevant areas, including respiratory infectious diseases, respirators/masks, protective clothing and PPE, protective efficiencies, physiological stresses, subjective evaluations of respirators/masks and protective clothing, and physical properties of fabric used for respirators/masks and protective clothing. To achieve the objective of this research, a systematic study has been carried out to investigate the performance of two critical PPE items: masks and personal protective clothing (PPC). The study of masks was carried out to investigate the in-vivo performances of N95 and surgical masks commonly available with or without nano-functional treatments, as well as two types of new masks with exhaust valves and holes (Masks A and B). Additionally, we verified how the virus-laden respiratory droplets transmit through masks. Five healthy male and five healthy female participants performed intermittent exercise on a treadmill while wearing the protective masks in a climate chamber controlled at an air temperature of 25°C and a relative humidity of 70%. During this period, the a KCl-Fluorescein solution as a surrogate for a viral solution was sprayed onto the masks twice at a distance of 100 cm every 10 minutes for 14 times in total. The results showed that N95 respirators had significantly lower air permeability and water vapor permeability, but higher filtration efficiency (97%) comparing with surgical masks (95%). Nano-masks show stronger water repellency and antibacterial activities, but no difference in usability, compared with normal N95 and surgical masks. By changing the design of mask, both masks A and B had near or over 99% protective efficiency achieved simply by locating the breathing pathways (exhaust valves and holes) to the back of mask. Furthermore, the findings of the mask physiological experiment and subjective ratings indicated that the subjects had significantly lower average heart rates, the microclimate and skin temperatures and absolute humidity inside the mask, and lower ratings for perception of humidity, heat, breath resistance, overall discomfort and other sensations when wearing nano-treated and untreated surgical masks than when wearing nano-treated and untreated N95 masks. Subjective preference for the nano-treated surgical masks was the highest. Subjects had lower maximum heart rate, temperatures and absolute humidities (surface of the mask, microclimate inside the mask, the chest wall skin and microclimate), the ear canal temperature (Tear), subjective ratings and mist over the glasses with mask A than with mask B. Preference was for mask A. The ear canal temperature showed significant augmentation along with increased temperature and humidity inside the mask microclimate. The mask microclimate temperature also affected significantly the chest microclimate temperatures. Perceived wetness and fatigue had significant effects on perceived overall discomfort. The results obtained suggest the tested masks can induce significantly different temperatures and humidity in the microclimates of masks, which have profound influences on heart rate, thermal stress and subjective perception of discomfort. By conducting a simulating experiment to wear four types of PPE on a plastic mannequin, it was found that protective performance of PPE suggest that fabric construction, water repellency, resistance to liquid water penetration, thickness, density and pore size, in combination with the structural design of PPE ensemble, contribute to protective clothing performance as we found when. Wear trials were performed to examine the effects of wearing five types of PPE on the physiological stresses and the subjective sensations in a simulated environment closely replicating health care workers. Ten healthy subjects carried out the simulation including exercising on a treadmill, working on a computer, and moving a mannequin wearing five types of PPE (PPE1 to PPE5). The results showed that, when ensembles similar to PPE1 are used in warm environments, the result could be higher physiological stress state to the wearer, including the increases in ear canal temperature, skin temperatures, clothing microclimates, heart rate and adrenaline secretion. Results of the subjective sensations show that when ensembles similar to PPE 1 and PPE 2 with face shield and hood are used in warm environments, the subjects express less favorable subjective responses in terms of the sensations of discomfort, usability, overall satisfaction level and preference. The discomfort related sensations could be mostly explained by the air-tightness of PPE. The weight and construction may be responsible for the usability differences between the PPEs. The fitness of the mask is an important factor affecting the overall discomfort under the mask and overall satisfaction level for PPE ensemble. Moreover, there were significantly different cumulative one-way transport capacity, liquid moisture management capacity and water vapour permeability between PPE1 and 2. The physical mechanisms involved were investigated by conducting computer simulations using thermal software of computer aided design (CAD). When we measured blood flow volume of skin, sweating rate and regulative heat loss by sweating, heat loss by vaporized water diffusion and evaporative heat loss after both exercises, we found significant differences between PPE1 and 2. The results illustrate that liquid sweat transferred from next to the skin surface to the opposite surface quickly due to the fabric moisture transport properties (MTP), thus speeding up the processes of evaporation and heat dissipation. It was concluded that the fabric's MTP, when incorporated into protective clothing, may well be the main physiological mechanism for reducing heat stress when PPE structures are similar. Through this systematic study, an evaluation system of mask and PPE performance has been developed for assessing their overall performances scientifically, including protection, physiological stresses, subjective comfort and environmental impact and cost.