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Positive Pressure Protective Gown

Sep. 08, 2020

The new crown virus is positioned as a virus with a biosafety level of level 3, and the lethality rate and other parameters are lower than that of a level 4 virus. Viruses classified as level 4 in biosafety, such as Ebola, have a fatality rate of 73% that ravages Africa. Facing the offensive of the virus, what should humanity do? At present, the most advanced positive pressure protective gown, coupled with a mask made of a polyurethane composite fabric that is only 0.3 mm thick, which is called black technology, can subdue the fourth-level virus.


In the new crown epidemic, the material we are most short of is not masks, but protective clothing. The production of masks is relatively simple, and the speed of mass production has increased rapidly, but the protective clothing is different. There are different protection standards for different infectious diseases, resulting in different protective capabilities of the protective gown.


The earliest record of using protective gown can be traced back to the 1880s, when a German doctor performed an operation wearing protective gown. Of course, the main reason he wears protective gown is to avoid staining his clothes, and the protective gown is just ordinary cotton fabric. By the time of World War II, the U.S. military developed a dense fabric with a higher density, which was woven with mercerized yarns of American long-staple cotton with an interval of less than 5 microns between each yarn, and pyridine quaternary amine was used at the same time. Salt or melamine hydrophobe is water repellent. In this way, this fabric has the ability to impede water and becomes a field (surgical) isolation protective suit for the US military. This process is the manufacturing technology of primary protective gown. It is based on high-density fabric and coated with a water-repellent coating on the surface to form a primary protective system. However, this kind of protective clothing has poor protection ability, low penetration resistance and water pressure resistance, and poor air permeability.


These defects led to the second technological innovation of protective gown. In 1976, a US company developed spunbond nonwovens and meltblown nonwovens to merge, and successfully developed spunbond materials for the surface layer and spunbond core material. -Meltblown-spunbond three-layer composite protective gown fabric. The fabric absorbs the characteristics of good filtering effect of meltblown nonwoven fabric and high strength of spunbonded nonwoven fabric. The manufactured protective clothing has high strength, good air permeability, and can filter pathogenic bacteria to a certain extent. The emergence of spunbond-meltblown-spunbond composite fabrics also has a shortcoming, that is, it cannot meet the epidemic prevention needs of high-infectious diseases. The US Gore company uses PTFE microporous film as raw material to develop a PTFE film, covering the outer layer of protective gown, and the microporous process can be controlled within a range of less than 0.3 microns. This is because the 0.3-micron pore size can radiate moisture from the body, but it can isolate the blood sprayed by the patient.


With the development of polymer materials and technological improvement, polyethylene microporous film has become the current mainstream protective clothing manufacturing material. By adding calcium carbonate particles to polyethylene, the protective clothing manufactured through this process can also isolate harmful substances such as droplets, aerosols, and so on. Therefore, it can be used for SARS virus epidemic prevention needs. At this point, humans finally have a biosafety level that can resist Protective clothing for level 3 viruses. But this is not enough. In February 2014, West Africa broke out the most serious Ebola virus epidemic, which caused more than 5,000 deaths and 13,000 infections in just a few months. The highest mortality rate reached 73%. One of the most fatal infectious diseases discovered so far.


The countries where the Ebola virus broke out in 2014 were impoverished areas such as Guinea, Liberia, and Sierra Leone. The total GDP of these three countries was only 17 billion U.S. dollars, with a total population of 25 million, making them one of the least developed countries in the world. If it is absolutely impossible to control Ebola virus by relying solely on West African technology and medical power, and to control Ebola virus, in addition to treatment, the first hurdle is to have a more advanced positive pressure protective suit.


Ebola virus is one of the most dangerous viruses facing human beings, and it is at the highest level of biosafety: level 4. Although HIV has a high fatality rate, its transmission routes are restricted and there is no danger of Ebola. Biosafety level 4 viruses have the ability to spread through the air, and there are no effective vaccines and treatments. Medical staff need to undergo extremely strict training and operations before they can engage in such anti-virus related work.


The Ebola virus was first discovered in 1976, and it continues to erupt to this day. The most critical reason is that isolation and protection measures are not in place. The virus has an incubation period of up to 21 days, but it generally dies within 14 days of infection and has a short course. , Rapid outbreak and other characteristics, once an outbreak can destroy the local national economy and public health system. West African countries are in the poorest areas in the world. The United Nations and the International Red Cross have established rapid diagnosis and on-site isolation systems in West Africa to effectively curb the spread of Ebola. Among them, the most important link in the on-site isolation system is that when medical staff come into contact with virus carriers, they need to wear the most advanced positive pressure protective gown.


This kind of protective gown  is also generally used for biochemical operations, and belongs to the multi-layered one-piece biological protective clothing. As mentioned earlier, protective gown made of polyethylene microporous film also needs to undergo a process to prevent phage penetration. In the United States NFPA 1999-2018 standard and the European Union EN 14126-2003 standard, both require biological permeability, but they can only prevent phage penetration breakthroughs within a certain period of time, and cannot be used to prevent Ebola virus. It can be seen from this that positive pressure protective gown is different from traditional protective gown in process requirements.


Positive pressure protective gown is a biological safety level four, full-body protective clothing. The head, torso and limbs are all wrapped in the protective clothing, and air is supplied into the protective suit in the form of electric air supply. The surface material is a multi-purpose laminated film material developed in Switzerland, with a thickness of 100 microns and a mass of 100 to 150 grams per square meter. The transparent hood is covered with a transparent polyurethane film material with a thickness of 0.3 mm.


The mask is the most likely part of the protective gown to contact the patient, so its manufacturing process is more complicated. It is necessary to prepare the polyurethane mother liquor into 0.1 mm and 0.2 mm films, respectively, and make them under 35MPa pressure. The polyurethane and the mask are combined to form a polyurethane composite fabric. The thickness does not exceed 0.3 mm, and the mass per square meter is 180 grams. The medical staff does not feel too heavy when wearing the head.


The composite fabric also needs to have the ability to resist tearing, because resistance and struggle may occur in the process of controlling the patient. Once the mask is broken, the medical staff is likely to be infected. In terms of protective performance, the transparent hood can isolate bacteriophages, poliovirus, blood, etc., and microorganisms cannot penetrate the mask under a hydrostatic pressure of 20kPa.


The emergence of positive pressure protective clothing technology has allowed the Ebola virus to be effectively controlled, greatly reducing the probability of infection of medical staff, and has contributed to the control of the Ebola virus epidemic in West Africa. Because Ebola virus can exist in any part of the patient, including blood, body fluids, skin, excrement, and vomit. Any object used by the patient may be a potential source of infection. If there is no positive pressure protective clothing, then The Ebola virus is likely to be raging around the world.


Positive pressure protective gown should be said to be the most advanced technology and innovation in the field of protective gown. It abandons the traditional protection strategy and uses the electric air supply system on the back to send air into the protective gown to achieve positive pressure inside the protective clothing. On the one hand, it can be tested whether the protective clothing is completely isolated from the outside world. If there are gaps or the protective gown is damaged, it will not be able to achieve complete isolation; on the other hand, it is also convenient for spraying and washing.



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