Mechanical filters, a part of particulate respirators, 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 filters, a part of particulate respirators, 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: [4] [5]
More obscure mechanisms include:
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]
Mechanical filters can be made of a fine mesh of synthetic polymer fibers. [8] [9] The fibers are produced by melt blowing. [10] The fibers are charged as they are blown to produce an electret, [11] and then layered to form a nonwoven polypropylene fabric. [8] [9]
Filtering facepiece respirators are discarded when they become unusable due to damage, dirt, or excessive breathing resistance. [12] Filtering facepieces are typically simple, light, single-piece, half-face masks and employ the first three mechanical filter mechanisms in the list above to remove particulates from the air stream. The most common of these is the white, disposable Standard N95 variety; another type is the Surgical N95 mask. It is discarded after single use or some extended period depending on the contaminant. NIOSH recommends not reusing filtering facepieces in biosafety level 2 or 3 laboratories. [13]
Elastomeric respirators, also called reusable air-purifying respirators, [14] 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. [15]
Elastomeric respirators consist of a reusable mask that seals to the face, with exchangeable filters. [16] [17] Elastomeric respirators can be used with chemical cartridge filters that remove gases, mechanical filters that retain particulate matter, or both. [18] As particulate filters, they are comparable [16] (or, due to the quality and error-tolerance of the elastomeric seal, possibly superior [18] ) to filtering facepiece respirators such as most disposable N95 respirators and FFP masks. [16]Under the current revision of Part 84 established in 1995, NIOSH established nine classifications of approved particulate filtering respirators based on a combination of the respirator series and efficiency level. The first part of the filter's classification indicates the series using the letters N, R, or P to indicate the filter's resistance to filtration efficiency degradation when exposed to oil-based or oil-like aerosols (e.g., lubricants, cutting fluids, glycerine, etc.). [19] [20] [21] Definitions and intended use for each series is indicated below. [22]
The second value indicates the minimum efficiency level of the filter. When tested according to the protocol established by NIOSH each filter classification must demonstrate the minimum efficiency level indicated below.
| Particulate | Respirator Class | Minimum Efficiency Level | Permitted for TB |
|---|---|---|---|
| NaCl (N) or DOP (R,P) | N95, R95, P95 | 95% | Yes |
| N99, R99, P99 | 99% | ||
| N100, R100, P100, HE | 99.97% |
All respirator types are permitted for TB. [23] [24] Class-100 filters can block asbestos. [25] For N type filters, a 200 mg load of NaCl is used, with and undefined service time. For R type filters, a 200 mg of DOP is used, with a defined service time of "one work shift". For P type filters, an indefinite amount of DOP is used until filtration efficiency stabilizes. [26] P100 filters, under 42 CFR part 84, are the only filters permitted to be magenta in color. [27] HE (high-efficiency) labeled filters are only provided for powered air-purifying respirators. HE-marked filters are 99.97% efficient against 0.3 micron particles and are oil-proof. [28] [29] [30]
Since filters are tested against the by definition most penetrating particle size of 0.3 μm, an APR with a P100 classification would be at least 99.97% efficient at removing particles of this size. [21] Particles with a size both less than and greater than 0.3 μm may be filtered at an efficiency greater than 99.97%. [31] [32] However, this may not always be the case, as the most penetrating particle size for N95s was measured to be below 0.1 μm, as opposed to the predicted size of between 0.1 and 0.3 μm. [33]
The EN 149 standard defines performance requirements for three classes of particle-filtering half masks: FFP1, FFP2 and FFP3. The protection provided by an FFP2 (or FFP3) mask includes the protection provided by a mask of the lower-numbered classes.
A mask conforming to the standard must have its class written on it, along with the name of the standard and its year of publication, as well as any applicable option codes, e.g. “EN 149:2001 FFP1 NR D”. Some manufacturers use in addition the colour of the elastic band to identify the mask class, however, the EN 149 standard does not specify any such colour coding and different manufacturers have used different colour schemes.
| Class [34] | Filter penetration limit (at 95 L/min air flow) | Inward leakage | Typical elastic band |
|---|---|---|---|
| FFP1 | 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 |
European standard EN 143 defines the 'P' classes of particle filters that can be attached to a face mask. These filters are typically used on reusable respirators, like elastomeric respirators. [35]
| Standard | Class | Filter type | Filter penetration limit (at 95 L/min air flow) | Inward leakage | Typical elastic band |
|---|---|---|---|---|---|
| EN 14683 [36] | 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 | ||||
| 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 |
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)": [38]
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: [52] [53]
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. [63] 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; [63] 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. [64] Some hospitals have been stockpiling used masks as a precaution. [65] 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"). [66]
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. [63] Fit and comfort do not seem to be harmed by UVGI, moist heat incubation, and microwave-generated steam. [63]
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 [63] (made under a vacuum with radio waves [67] ). The static electrical charge on the microfibers 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. [63]
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. [63] Where enough masks are available, cycling them and reusing a mask only after letting it sit unused for five days is preferred. [64]
It has been shown that masks can also be sterilized by ionizing radiation. [68] 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. [69]
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. Gas masks only protect the user from ingesting or inhaling chemical agents, as well as preventing contact with the user's 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, chemical, 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.
HEPA filter, also known as high-efficiency particulate absorbing filter and high-efficiency particulate arrestance filter, is an efficiency standard of air filters.
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.
The term immediately dangerous to life or health (IDLH) is defined by the US National Institute for Occupational Safety and Health (NIOSH) as exposure to airborne contaminants that is "likely to cause death or immediate or delayed permanent adverse health effects or prevent escape from such an environment." Examples include smoke or other poisonous gases at sufficiently high concentrations. It is calculated using the LD50 or LC50. The Occupational Safety and Health Administration (OSHA) regulation defines the term as "an atmosphere that poses an immediate threat to life, would cause irreversible adverse health effects, or would impair an individual's ability to escape from a dangerous atmosphere."
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.
An N95 respirator is a disposable filtering facepiece respirator or reusable elastomeric filter 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 under 42 CFR Part 84, effective July 10, 1995. This standard does not require that the respirator be resistant to oil; two other standards, R95 and P95, add that requirement. The N95 type is the most common 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"), and, for most filtering facepiece respirators, a "TC" approval number of the form 84A-####, the approval number. All N95 respirators, regardless of type, 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 breathing, speaking, coughing, sneezing or singing. Multiple source control techniques can be used in hospitals, but for the general public wearing personal protective equipment during epidemics or pandemics, respirators provide the greatest source control, followed by surgical masks, with cloth face masks recommended for use by the public only when there are shortages of both respirators and surgical masks.
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.
The European respirator standards refer to the filtering half mask classification by EN 149, EN 14683, and EN 143, a European standard of testing and marking requirements for respirators. 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. They may be equipped with a backup air tank in case the air-line gets cut.
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.
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