Study On Safety And Thermal Comfort Of Active Purification Air - Conditioned Bio - Protective Clothing Under High - Risk Biological Pollution

As one of the safest personal bio-protective equipment, powered air-purifying suit is mainly applied for the personal protection of research staff working in a biological safety laboratory or rescue workers dealing with the sudden epidemic which is of great contribution to the promotion of epidemic experimental research and emergency rescue force. However, due to a late start in China, theoretical study about protection factor and comfort of personal bio-protective equipment is underdeveloped. So far there is no technical standard and test method applied to the powered air-purifying suit, which seriously hampered its development. Therefore, this paper aims to build a scientific testing platform for the powered air-purifying suit and study its protection performance and thermal comfort, laying a theoretical foundation for the development.In this study a full-size motion simulation manikin was built according to the common operation action during use of the powered air-purifying suit. The manikin wearing a powered air-purifying suit could act like a real person under the bio-aerosol environment, and the first dynamic testing platform of powered air-purifying suit in China was built along with the use of an environment controlled airtight chamber. Based on this testing platform, a concentration attenuation model of Staphylococcus aureus aerosol, which was chosen as the testing media, was obtained by studying the sedimentation, the decline and the filtration of biological particles. Then an effective concentration supplement strategy was made according to the concentration attenuation model to stabilize the internal concentration within the given range making the dynamic detection of the protection factor of powered air-purifying suit under bio-hazard environment possible. Based on the testing platform and reasonable testing method, the protection factor of powered air-purifying suit was tested. The results showed that the the protection factor of the powered air-purifying suit is beyond 5×105, which meets its safety requirements.The stable positive pressure inside the powered air-purifying suit is the key of reliable protection performance. However, body movements would impose disturbance on the internl pressure during use. A high frequency differential pressure transmitter was used here to sample the pressure inside the suit. And the pressure fluctuation caused by breath and body movements was studied using a breath simulator and the manikin. The results show that the pressure fluctuation inside the powered air-purifying suit was mainly caused by the deformation of the suit, which was affected by the movement form, movement range and movement speed. During movement, the inner pressure would raise due to the squeezing of suit and descend due to the pull back of limbs and reshaping of the suit. Local damage on the powered air-purifying suit would cause irreversible pressure loss. This paper studied the pressure change of the powered air-purifying suit after local damaged regarding the damage size, damage form and damage location. The results showed that the pressure loss caused by local damage depends on the leakage area, which was mainly decided by the damage size and form and affected by the damage location while moving. Through the study of dynamic pressure fluctuation under different damages, the formation and function mechanism of instantaneous negative pressure inside the powered air-purifying suit were well understood.When the pressure loss caused by the local damage had a synergy effect with the pressure fluctuation caused by the movement, the instantaneous pressure inside the suit may be lower than 0pa, which may leading to safety risks. Bio-aerosol exposure experiments were carried out to test the protection factor of the damaged suit. The results showed that instantaneous negative pressure is necessary but not sufficient for leakage. Because the instantaneous negative pressure is necessary for the leakage, the pressure and leakage have indirect association. To realize the real-time risk assessment through pressure data, by defining the multiplication of negative pressure and sampling length as risk factor, the relationship between the pressure and leakage could be built. And compared the calculated leakage with the pathogenic concentration of common high-risk infectious disease, the quantitative safety risks could be assessed. According to the local damage which caused negative pressure, coping strategies such as raising the air supply and movement modification were proposed to reduce the possibility of instantaneous negative pressure and avoid the safety risks.Thermal comfort is another major index of powered air-purifying suit. Herein, PRO/Engineer was used to build the 3-D model of the powered air-purifying suit. Based on the model, flow vector distribution and temperature distribution were simulated using the Fluent. At the same time thermal comfort experiments were carried out by personnel wearing powered air-purifying suit and compared with the simulation results. The results indicate that flow distribution inside the suit was not uniform, and the air convection near arms and feet were insufficient, making the local temperature much higher. Wearing under high temperature environment would impose thermal stress on people. Regarding the thermal comfort problem of the powered air-purifying suit, modifying the flow distribution is a feasible solution to improve the local hot zone. Herein, increasing exhaust valves and modifying the air supply were suggested to improve the thermal comfort of powered air-purifying suit.The fabric of the powered air-purifying suit is another major factor concerning the thermal comfort. To guarantee the strict air tightness, antimicrobial polyurethane layers were coated on both sides of the fabric. However, the moisture could not exhaust out of the suit from the fabric either, which deteriorated the wearing comfort. Herein, a dual-spinneret electrospinning method was used to prepare hybrid nanofibers of waterborne polyurethane(WPU) and poly(vinyl alcohol)(PVA) with silver nanoparticles(Ag NPs) to replace the polyurethane layer of the inner fabric. Because the nanofiber mats have bigger specific surface area than polyurethane layers, which increased the contact area of antimicrobial agents and the adsorption area of moisture, the hybrid nanofiber mats showed better antimicrobial property and hygroscopicity than the layers in the inhibition ring test and oven test. At the same time, both waterborne polyurethane and poly(vinyl alcohol) are water soluble material, no volatile organic solvents were used in the electrospinning, which was cost-effective and eco-friendly. These properties make the hybrid nanofiber mats potential to optimize the fabric of the powered air-purifying suit.