Mechanical filters are a class of filter for air-purifying respirators that mechanically stops particulates from reaching the wearer's nose and mouth. They come in multiple physical forms.
Mechanical filter respirators retain particulate matter such as dust created during woodworking or metal processing, when contaminated air is passed through the filter material. Wool is still used today as a filter, along with plastic, glass, cellulose, and combinations of two or more of these materials. Since the filters cannot be cleaned and reused and have a limited lifespan, cost and disposability are key factors. Single-use, disposable and replaceable-cartridge models exist. [3]
Mechanical filters remove contaminants from air in the following ways:
Considering only particulates carried on an air stream and a fiber mesh filter, diffusion predominates below the 0.1 μm diameter particle size. Impaction and interception predominate above 0.4 μm. In between, near the most penetrating particle size of 0.3 μm, diffusion and interception predominate. [3]
For maximum efficiency of particle removal and to decrease resistance to airflow through the filter, particulate filters are designed to keep the velocity of air flow through the filter as low as possible. This is achieved by manipulating the slope and shape of the filter to provide larger surface area.[ citation needed ]
High-efficiency particulate air (HEPA)filters are all filters meeting certain efficiency standards. A HEPA filter must remove at least 99.97% (US) or 99.95% (EU) of all airborne particulates with aerodynamic diameter of 0.3 μm. Particles both smaller and larger are easier to catch, and thus removed with a higher efficiency. [6] [7] [8] People often assume that particles smaller than 0.3 microns would be more difficult to filter efficiently; however, the physics of Brownian motion at such smaller sizes boosts filter efficiency (see figure). [2]
Mechanical filters can be made of a fine mesh of synthetic polymer fibers. [9] [10] The fibers are produced by melt blowing. [11] The fibers are charged as they are blown to produce an electret, [12] and then layered to form a nonwoven polypropylene fabric. [9] [10]
Some masks have check valves, [13] that let the exhaled air go out unfiltered. The certification grade of the mask (as N95 or FFP2) is about the mask itself and it does not warrant any safety about the air that is expelled by the wearer through the valve. A mask with valve will reduce inwards leakages, thus improving the wearer protection. [13]
Unfiltered-exhalation valves are sometimes found in both filtering facepiece [13] and elastomeric respirators; [14] PAPRs cannot by nature ever filter exhaled air. [15] As a result, these masks are believed to be incapable of source control, which is protecting others against an infection in the wearer's breath. [14] They are not generally designed for healthcare use, as of 2017 [update] . [16] Despite the aforementioned belief, a 2020 research by the NIOSH and CDC shows that an uncovered exhalation valve already provides source control on a level similar to, or even better than, surgical masks. [17]
During the COVID-19 pandemic, masks with unfiltered-exhalation valves did not meet the requirements of some mandatory mask orders. [18] [19] It is possible to seal some unfiltered exhalation valves [20] or to cover it with an additional surgical mask; this might be done where mask shortages make it necessary. [21] [22]
Filtering facepiece respirator (FFPs) are disposable face masks produced from a whole piece of filtering material. FFPs (such as N95 masks) are discarded when they become unsuitable for further use due to considerations of hygiene, excessive resistance, or physical damage. [23]
Mass production of filtering facepieces started in 1956. The air was purified with nonwoven filtering material consisting of polymeric fibers carrying a strong electrostatic charge. Respirator was used in nuclear industry, and then in other branches of economy. For ~60 years, more than 6 billion respirators were manufactured. [24] Unfortunately, the developers overestimated the efficiency (APF 200-1000 compared to the modern value of 10–20), which led to serious errors in the choice of personal protective equipment by employers.
Elastomeric respirators are reusable devices with exchangeable cartridge filters that offer comparable protection to N95 masks. [25] The filters must be replaced when soiled, contaminated, or clogged. [14]
They may have exhalation valves. Full-face versions of elastomeric respirators seal better and protect the eyes. Fitting and inspection is essential to effectiveness. [14]
PAPRs are masks with an electricity-powered blower that blows air through a filter to the wearer. Because they create positive pressure, they need not be tightly fitted. [26] PAPRs typically do not filter exhaust from the wearer. [27]
The electrostatic filters in respirators are much easier to breathe through than cloth masks, however, when respirators are worn with additional coverings, such as surgical mask material, then they can make breathing harder for the wearer. As a result, exposure to carbon dioxide may exceed its OELs [ citation needed ] (0.5% by volume for 8-hour shift; 1.4% for 15 minutes exposure [28] ), with CO2 levels inside reaching up to 2.6% for elastomeric respirators and up to 3.5 for FFRs. Mean values for several models; some models may provide a stronger exposure to carbon dioxide. These values are comparable to the CO2 levels that normally occur within the trachea, and the volume inside a respirator facepiece is a fraction of the total volume inhaled with each breath, so the total CO2 concentration for each breath is much less than the concentration within the small volume of the facepiece itself. [lower-alpha 1] [29] [30] [31] Skin irritation and acne (from humidity and skin contact) can be an annoyance. [32] The UK HSE textbook recommends limiting the use of respirators without air supply to 1 hour, [33] while OSHA recommends respirator use for up to eight hours.
Almost all filtration methods perform poorly outside when environmental airborne water levels are high, causing saturation and clogging, increasing breathing resistance, and the collection of water on the electrostatic filter fibers can reduce the efficiency of the filter. Bidirectional air flow (as used on masks without an exhalation valve) compounds this problem further. Design standards are typically used for 'indoor' settings only.[ citation needed ]
In the United States, the National Institute for Occupational Safety and Health defines the following categories of particulate filters according to their NIOSH air filtration rating. [34] (Categories highlighted in blue have not actually been applied to any products.)
Oil resistance | Rating | Description |
---|---|---|
Not oil resistant | N95 | Filters at least 95% of airborne particles |
N99 | Filters at least 99% of airborne particles | |
N100 | Filters at least 99.97% of airborne particles | |
Oil resistant | R95 | Filters at least 95% of airborne particles |
R99 | Filters at least 99% of airborne particles | |
R100 | Filters at least 99.97% of airborne particles | |
Oil proof | P95 | Filters at least 95% of airborne particles |
P99 | Filters at least 99% of airborne particles | |
P100 | Filters at least 99.97% of airborne particles |
Additionally, HE (high-efficiency) filters are the class of particulate filter used with powered air-purifying respirators. These are 99.97% efficient against 0.3 micron particles, the same as a P100 filter. [35] [36] [37]
During the COVID-19 pandemic, the US Occupational Safety and Health Administration issued an equivalency table, giving similar foreign standards for each US standard. [38]
In the United States, N95 respirators are designed and/or made by companies such as 3M, Honeywell, Cardinal Health, Moldex, [39] Kimberly-Clark, Alpha Pro Tech, [40] Gerson, [41] Prestige Ameritech and Halyard Health. In Canada, N95s are made by AMD Medicom, [42] Vitacore, [43] Advanced Material Supply, [44] Eternity [45] and Mansfield Medical. [46] The Taiwanese company Makrite makes N95s as well as similar respirators for a number of other countries. [47] Degil is a label for some of Makrite's respirators.
European standard EN 143 defines the 'P' classes of particle filters that can be attached to a face mask, and European standard EN 149 defines the following classes of "filtering half masks" or "filtering facepieces" (FFP), that is respirators that are entirely or substantially constructed of filtering material: [48]
Standard | Class | Filter type | Filter penetration limit (at 95 L/min air flow) | Inward leakage | Typical elastic band |
---|---|---|---|---|---|
EN 149 | FFP1 | Mask | Filters at least 80% of airborne particles | <22% | yellow |
FFP2 | Filters at least 94% of airborne particles | <8% | blue or white | ||
FFP3 | Filters at least 99% of airborne particles | <2% | red | ||
EN 143 | P1 | Attachment | Filters at least 80% of airborne particles | N/A | N/A |
P2 | Filters at least 94% of airborne particles | ||||
P3 | Filters at least 99.95% of airborne particles | ||||
EN 14683 [49] | Type I | Mask | Less than 98% droplet filtration, intended for use by patients | N/A | N/A |
Type II | Not fluid-resistant, 98% droplet filtration, intended for use by healthcare workers in droplet-free environments | ||||
Type IIR | Fluid-resistant, 98% droplet filtration, surgical |
Both European standard EN 143 and EN 149 test filter penetration with dry sodium chloride and paraffin oil aerosols after storing the filters at 70 °C (158 °F) and −30 °C (−22 °F) for 24 h each. The standards include testing mechanical strength, breathing resistance and clogging. EN 149 tests the inward leakage between the mask and face, where 10 human subjects perform 5 exercises each. The truncated mean of average leakage from 8 individuals must not exceed the aforementioned values. [50] : § 8.5
In Germany, FFP2 respirators are made by companies such as Dräger, Uvex [51] and Core Medical. [52] In Belgium, Ansell [53] makes FFP2 masks. In France, the company Valmy [54] makes them. In the United Kingdom, the company Hardshell [55] has recently begun making FFP2 masks.
Respirator standards around the world loosely fall into the two camps of US- and EU-like grades. According to 3M, respirators made according to the following standards are equivalent to US N95 or European FFP2 respirators "for filtering non-oil-based particles such as those resulting from wildfires, PM 2.5 air pollution, volcanic eruptions, or bioaerosols (e.g. viruses)": [56]
The NPPTL has also published a guideline for using non-NIOSH masks instead of the N95 in the COVID-19 response. The OSHA has a similar document. The following respirator standards are considered similar to N95 in the US: [72] [73]
This section is missing information about filter life requirement (performance after prescribed amount of dust-loading) — currently describes strap failure only.(December 2021) |
Hard filtering facepiece respirator masks are generally designed to be disposable, for 8 hours of continuous or intermittent use. One laboratory found that there was a decrease in fit quality after five consecutive donnings. [13] Once they are physically too clogged to breathe through, they must be replaced.
Hard filtering facepiece respirator masks are sometimes reused, especially during pandemics, when there are shortages. Infectious particles could survive on the masks for up to 24 hours after the end of use, according to studies using models of SARS-CoV-2; [13] In the COVID-19 pandemic, the US CDC recommended that if masks run short, each health care worker should be issued with five masks, one to be used per day, such that each mask spends at least five days stored in a paper bag between each use. If there are not enough masks to do this, they recommend sterilizing the masks between uses. [81] Some hospitals have been stockpiling used masks as a precaution. [82] The US CDC issued guidelines on stretching N95 supplies, recommending extended use over re-use. They highlighted the risk of infection from touching the contaminated outer surface of the mask, which even professionals frequently unintentionally do, and recommended washing hands every time before touching the mask. To reduce mask surface contamination, they recommended face shields, and asking patients to wear masks too ("source masking"). [83]
Apart from time, other methods of disinfection have been tested. Physical damage to the masks has been observed when microwaving them, microwaving them in a steam bag, letting them sit in moist heat, and hitting them with excessively high doses of ultraviolet germicidal irradiation (UVGI). Chlorine-based methods, such as chlorine bleach, may cause residual smell, offgassing of chlorine when the mask becomes moist, and in one study, physical breakdown of the nosepads, causing increased leakage. [13] Fit and comfort do not seem to be harmed by UVGI, moist heat incubation, and microwave-generated steam. [13]
Some methods may not visibly damage the mask, but they ruin the mask's ability to filter. This has been seen in attempts to sterilize by soaking in soap and water, heating dry to 160 °C (320 °F), and treating with 70% isopropyl alcohol, and hydrogen peroxide gas plasma [13] (made under a vacuum with radio waves [84] ). The static electrical charge on the microfibers (which attracts or repels particles passing through the mask, making them more likely to move sideways and hit and stick to a fiber[ citation needed ]; see electret) is destroyed by some cleaning methods. UVGI (ultraviolet light), boiling water vapour, and dry oven heating do not seem to reduce the filter efficiency, and these methods successfully decontaminate masks. [13]
UVGI (an ultraviolet method), ethylene oxide, dry oven heating and vaporized hydrogen peroxide are currently the most-favoured methods in use in hospitals, but none have been properly tested. [13] Where enough masks are available, cycling them and reusing a mask only after letting it sit unused for five days is preferred. [81]
It has been shown [85] that masks can also be sterilized by ionizing radiation. Gamma radiation and high energy electrons penetrate deeply into the material and can be used to sterilize large batches of masks within a short time period. The masks can be sterilized up to two times but have to be recharged after every sterilization as the surface charge is lost upon radiation.
A recent development is a composite fabric that can deactivate both biological and chemical threats [86]
A gas mask is an item of personal protective equipment used to protect the wearer from inhaling airborne pollutants and toxic gases. The mask forms a sealed cover over the nose and mouth, but may also cover the eyes and other vulnerable soft tissues of the face. Most gas masks are also respirators, though the word gas mask is often used to refer to military equipment, the scope used in this article. The gas mask only protects the user from digesting, inhaling, and contact through the eyes. Most combined gas mask filters will last around 8 hours in a biological or chemical situation. Filters against specific chemical agents can last up to 20 hours.
Personal protective equipment (PPE) is protective clothing, helmets, goggles, or other garments or equipment designed to protect the wearer's body from injury or infection. The hazards addressed by protective equipment include physical, electrical, heat, chemicals, biohazards, and airborne particulate matter. Protective equipment may be worn for job-related occupational safety and health purposes, as well as for sports and other recreational activities. Protective clothing is applied to traditional categories of clothing, and protective gear applies to items such as pads, guards, shields, or masks, and others. PPE suits can be similar in appearance to a cleanroom suit.
A surgical mask, also known by other names such as a medical face mask or procedure mask, is a personal protective equipment used by healthcare professionals that serves as a mechanical barrier that interferes with direct airflow in and out of respiratory orifices. This helps reduce airborne transmission of pathogens and other aerosolized contaminants between the wearer and nearby people via respiratory droplets ejected when sneezing, coughing, forceful expiration or unintentionally spitting when talking, etc. Surgical masks may be labeled as surgical, isolation, dental or medical procedure masks.
A respirator is a device designed to protect the wearer from inhaling hazardous atmospheres including fumes, vapours, gases and particulate matter such as dusts and airborne pathogens such as viruses. There are two main categories of respirators: the air-purifying respirator, in which respirable air is obtained by filtering a contaminated atmosphere, and the air-supplied respirator, in which an alternate supply of breathable air is delivered. Within each category, different techniques are employed to reduce or eliminate noxious airborne contaminants.
A dust mask is a flexible paper pad held over the nose and mouth by elastic or rubber straps for personal comfort against non-toxic nuisance dusts. They are not intended to provide protection from toxic airborne hazards. The European FFP1 mask, the lowest-grade mechanical filter respirator available in the jurisdiction, is also used as a dust mask.
A respirator fit test checks whether a respirator properly fits the face of someone who wears it. The fitting characteristic of a respirator is the ability of the mask to separate a worker's respiratory system from ambient air.
A respirator cartridge or canister is a type of filter that removes gases, volatile organic compounds (VOCs), and other vapors from air through adsorption, absorption, or chemisorption. It is one of two basic types of filters used by air-purifying respirators. The other is a mechanical filter, which removes only particulates. Hybrid filters combine the two.
The National Personal Protective Technology Laboratory (NPPTL) is a research center within the National Institute for Occupational Safety and Health located in Pittsburgh, Pennsylvania, devoted to research on personal protective equipment (PPE). The NPPTL was created in 2001 at the request of the U.S. Congress, in response to a recognized need for improved research in PPE and technologies. It focuses on experimentation and recommendations for respirator masks, by ensuring a level of standard filter efficiency, and develops criteria for testing and developing PPE.
The NIOSH air filtration rating is the U.S. National Institute for Occupational Safety and Health (NIOSH)'s classification of filtering respirators. The ratings describe the ability of the device to protect the wearer from solid and liquid particulates in the air. The certification and approval process for respiratory protective devices is governed by Part 84 of Title 42 of the Code of Federal Regulations. Respiratory protective devices so classified include air-purifying respirators (APR) such as filtering facepiece respirators and chemical protective cartridges that have incorporated particulate filter elements.
A powered air-purifying respirator (PAPR) is a type of respirator used to safeguard workers against contaminated air. PAPRs consist of a headgear-and-fan assembly that takes ambient air contaminated with one or more type of pollutant or pathogen, actively removes (filters) a sufficient proportion of these hazards, and then delivers the clean air to the user's face or mouth and nose. They have a higher assigned protection factor than filtering facepiece respirators such as N95 masks. PAPRs are sometimes called positive-pressure masks, blower units, or just blowers.
The respiratory protective devices (RPD) can protect workers only if their protective properties are adequate to the conditions in the workplace. Therefore, specialists have developed criteria for the selection of proper, adequate respirators, including the Assigned Protection Factors (APF) - the decrease of the concentration of harmful substances in the inhaled air, which to be provided with timely and proper use of a certified respirator of certain types (design) by taught and trained workers, when the employer performs an effective respiratory protective device programme.
Respirators, also known as respiratory protective equipment (RPE) or respiratory protective devices (RPD), are used in some workplaces to protect workers from air contaminants. Initially, respirator effectiveness was tested in laboratories, but in the late 1960s it was found that these tests gave misleading results regarding the level of protection provided. In the 1970s, workplace-based respirator testing became routine in industrialized countries, leading to a dramatic reduction in the claimed efficacy of many respirator types and new guidelines on how to select the appropriate respirator for a given environment.
The health and safety hazards of nanomaterials include the potential toxicity of various types of nanomaterials, as well as fire and dust explosion hazards. Because nanotechnology is a recent development, the health and safety effects of exposures to nanomaterials, and what levels of exposure may be acceptable, are subjects of ongoing research. Of the possible hazards, inhalation exposure appears to present the most concern, with animal studies showing pulmonary effects such as inflammation, fibrosis, and carcinogenicity for some nanomaterials. Skin contact and ingestion exposure, and dust explosion hazards, are also a concern.
An N95 filtering facepiece respirator, commonly abbreviated N95 respirator, is a particulate-filtering facepiece respirator that meets the U.S. National Institute for Occupational Safety and Health (NIOSH) N95 classification of air filtration, meaning that it filters at least 95% of airborne particles that have a mass median aerodynamic diameter of 0.3 micrometers. This standard does not require that the respirator be resistant to oil; another standard, P95, adds that requirement. The N95 type is the most common particulate-filtering facepiece respirator. It is an example of a mechanical filter respirator, which provides protection against particulates but not against gases or vapors. An authentic N95 respirator is marked with the text "NIOSH" or the NIOSH logo, the filter class ("N95"), a "TC" approval number of the form XXX-XXXX, the approval number must be listed on the NIOSH Certified Equipment List (CEL) or the NIOSH Trusted-Source page, and it must have headbands instead of ear loops.
During the COVID-19 pandemic, face masks or coverings, including N95, FFP2, surgical, and cloth masks, have been employed as public and personal health control measures against the spread of SARS-CoV-2, the virus that causes COVID-19.
Source control is a strategy for reducing disease transmission by blocking respiratory secretions produced through speaking, coughing, sneezing or singing. Surgical masks are commonly used for this purpose, with cloth face masks recommended for use by the public only in epidemic situations when there are shortages of surgical masks. In addition, respiratory etiquette such as covering the mouth and nose with a tissue when coughing can be considered source control. In diseases transmitted by droplets or aerosols, understanding air flow, particle and aerosol transport may lead to rational infrastructural source control measures that minimize exposure of susceptible persons.
Elastomeric respirators, also called reusable air-purifying respirators, seal to the face with elastomeric material, which may be a natural or synthetic rubber. They are generally reusable. Full-face versions of elastomeric respirators seal better and protect the eyes.
FFP standards refer to the filtering half mask classification by EN 149, a European standard of testing and marking requirements for filtering half masks. FFP standard masks cover the nose, mouth and chin and may have inhalation and/or exhalation valves.
A supplied-air respirator (SAR) or air-line respirator is a breathing apparatus used in places where the ambient air may not be safe to breathe. It uses an air hose to supply air from outside the danger zone. It is similar to a self-contained breathing apparatus (SCBA), except that SCBA users carry their air with them in high pressure cylinders, while SAR users get it from a remote stationary air supply connected to them by a hose.
A breathing apparatus or breathing set is equipment which allows a person to breathe in a hostile environment where breathing would otherwise be impossible, difficult, harmful, or hazardous, or assists a person to breathe. A respirator, medical ventilator, or resuscitator may also be considered to be breathing apparatus. Equipment that supplies or recycles breathing gas other than ambient air in a space used by several people is usually referred to as being part of a life-support system, and a life-support system for one person may include breathing apparatus, when the breathing gas is specifically supplied to the user rather than to the enclosure in which the user is the occupant.
But she added you can easily cover the mask with a surgical mask or shield.
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