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Early surgical masks were made of multiple layers of gauze. In the early 20th century, surgical staff wore such gloves for the first time to prevent contamination of open surgical wounds. Over time, their design, functions, and uses have expanded. Today, surgical masks are widely used in various medical settings to protect patients from the breathing gas emissions of the wearer. A surgical mask is a disposable device that prevents users from releasing potential contaminants into the surrounding environment. In the United States, the US Food and Drug Administration (FDA) approved medical masks for sale. They may be labeled as surgical, laser, isolation, dental or medical procedure masks. They can wear masks or not. Since OSHA published the standard for bloodborne pathogens (29 CFR 1910.1030) in 1991, surgical masks have been recommended as part of general precautions to protect the wearer from direct splashes and splashes of infectious blood or body fluids. (The FDA provides more information about surgical masks.)
The first modern respirator was also developed in the early 20th century. The motivation for their development came from protecting miners from harmful dust and gas, soldiers from chemical warfare agents, and firefighters from smoke and carbon monoxide. In 1919, the U.S. Bureau of Mines issued the first performance standard for gas masks, which applies to self-contained breathing apparatus used in mines and gas masks used by soldiers to combat chemical warfare agents. Today, respirators can be found in many workplaces. Their use in medical institutions can be traced back to the 1990s, when people worried that employees would contract drug-resistant tuberculosis. Medical staff's illness and death during the severe acute respiratory syndrome (SARS) outbreak in the early 2000s have renewed attention to the use of respirators to treat certain infectious respiratory diseases. More recently, planning work for pandemic influenza in 2006-07 has led to a lot of discussions about the role of small particle inhalation in the spread of disease and the use of respirator to protect medical staff from airborne influenza particles. A list of all disposable masks or filter masks approved by niosh can be provided. NIOSH also maintains a database of all NIOSH approved respirators, regardless of the type of respirator-the list of certified equipment.
Whether the goal is to prevent the aerosol generated by the user from escaping outward, or to prevent harmful air particles from being transported inward, performance has two important aspects. First, the filter must be able to capture harmful particles, usually in a large range of sizes (<1> 100µm) in a series of airflows (approximately 10 to 100 L / min). Second, leakage must be prevented at the boundary between the mask and the face. However, without first ensuring that the filter functions well, it is impossible to ensure good sealing performance at the rear end.
Filtration performance
The filters used in modern surgical masks and respirators are considered natural "fibers"-flat nonwoven mats composed of fine fibers. Fiber diameter, porosity (the ratio of voids to fibers) and filter thickness all have an effect on the filter's ability to collect particles. In all fiber filters, there are three "mechanical" collection mechanisms to capture particles: inertial collision, interception and diffusion. The inertial collision and interception mechanism is responsible for collecting larger particles, while the diffusion mechanism is responsible for collecting smaller particles. In some fiber filters composed of charged fibers, the additional mechanism of electrostatic attraction also works. This mechanism helps to collect larger and smaller particle sizes. The latter mechanism is very important for filtering masks that meet strict NIOSH filtration efficiency and respiratory resistance requirements because it enhances particle collection without increasing respiratory resistance.
How does the filter collect particles?
These capture or filtering mechanisms are described as follows:
The diagram illustrates the inertial impact, interception, diffusion, and electrostatic attraction of the filtering mechanism. In each case, the fibers showed filtering particles.
Figure 1: Filtering mechanism
Inertial impact: Under this mechanism, particles with large inertia due to size or mass cannot follow the air flow, because the air flow will be redirected by the filter fiber. This mechanism is responsible for collecting larger particles.
Retention: When particles approach the filter fiber, they may be retained by the fiber. Again, this mechanism is responsible for collecting larger particles.
Diffusion: Small particles are constantly bombarded by air molecules, causing them to deviate from the airflow and come into contact with filter fibers. This mechanism is responsible for collecting smaller particles.
Electrostatic attraction: The opposite charged particles are attracted by the charged fiber. This collection mechanism does not support a specific granularity.
In all cases, once the particles come into contact with the filter fibers, it will be removed from the airflow and be strongly affected by the gravity of the molecules. Once these particles are collected, they are difficult to remove. As shown in Figure 2, none of the "mechanical" collection mechanisms (interception, impact, or diffusion) are particularly effective in particle size. This "most penetrating particle size" (MPPS) marks the best point for measuring filter performance. If the filter exhibits a high level of performance in MPPS, then particles regardless of size will be collected for higher performance.
This is probably the most misunderstood aspect of filter performance and is worth repeating. The filter does not act as a sieve. One of the best tests for filter performance is particle collection, which measures its most penetrating particle size, which ensures better performance of larger and smaller particles. In addition, the collection efficiency of filters is a function of particle size, regardless of whether they are bioaerosols or inert particles.
The graph shows the efficiency of the filter on the y-axis and the particle diameter (in microns) on the x-axis. Efficiency belongs to the 'proliferation and interception system'. https://www.  .html Quick
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