Mechanical filter respirator

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Filtering half mask with exhalation valve (class: FFP3) Atemluftfilter Einwegmaske.jpg
Filtering half mask with exhalation valve (class: FFP3)

Mechanical filter respirators are a class of respirator that removes particulates from the air using a filter that mechanically stops them from reaching the wearer's nose and mouth.

Contents

Mechanism of operation

Small particles zigzag due to Brownian motion, and are easily captured (diffusion). Large particles get strained out (interception), or have too much inertia to turn, and hit a fiber (impaction). Mid-size particles follow flowlines and are more likely to get through the filter; the hardest size to filter is 0.3 microns diameter. Filteration Collection Mechanisms.png
Small particles zigzag due to Brownian motion, and are easily captured (diffusion). Large particles get strained out (interception), or have too much inertia to turn, and hit a fiber (impaction). Mid-size particles follow flowlines and are more likely to get through the filter; the hardest size to filter is 0.3 microns diameter.
Filter mechanisms Filter collection mechanisms.svg
Filter mechanisms

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. [2]

Mechanical filters remove contaminants from air in the following ways:

  1. by interception when particles following a line of flow in the airstream come within one radius of a fiber and adhere to it; [2]
  2. by impaction, when larger particles unable to follow the curving contours of the airstream are forced to embed in one of the fibers directly; this increases with diminishing fiber separation and higher air flow velocity [2]
  3. by an enhancing mechanism called diffusion, where gas molecules collide with the smallest particles, especially those below 100 nm in diameter, which are thereby impeded and delayed in their path through the filter; this effect is similar to Brownian motion and increases the probability that particles will be stopped by either of the two mechanisms above; it becomes dominant at lower air flow velocities [2]
  4. by using electret filter material (usually, electrospun plastic fibers) to attract or repel particles with an electrostatic charge, so that they are more likely to collide with the filter surface
  5. by using certain coatings on the fibers that kill or deactivate infectious particles colliding with them (such as salt) [3]
  6. by using gravity and allowing particles to settle into the filter material (this effect is typically negligible); and [4]
  7. by using the particles themselves, after the filter has been used, to act as a filter medium for other particles.[ citation needed ]

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 0.3 μm most penetrating particle size, diffusion and interception predominate. [2]

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 ]

HEPA filter 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. [5] [ verification needed ][ relevant? – discuss ]

Cross-section of NIOSH-approved P95 filters used in metalworking operations. Even "clean" industrial processes often generate large amounts of harmful particulate matter and require breathing protection. NIOSH P95 cross section.jpg
Cross-section of NIOSH-approved P95 filters used in metalworking operations. Even "clean" industrial processes often generate large amounts of harmful particulate matter and require breathing protection.

Physical form

Filtering facepiece respirators

A half-face elastomeric air-purifying respirator. This kind of respirator is reusable, with the filters being replaced periodically. Air-Purifying Respirator.jpg
A half-face elastomeric air-purifying respirator. This kind of respirator is reusable, with the filters being replaced periodically.

Disposable filtering facepiece respirators (such as N95 masks) are discarded when they become unsuitable for further use due to considerations of hygiene, excessive resistance, or physical damage. [6]

Elastomeric respirators

Elastomeric respirators are reusable devices with exchangeable cartridge filters that offer comparable protection to N95 masks. [7] The filters must be replaced when soiled, contaminated, or clogged. [8]

They may have exhalation valves. Full-face versions of elastomeric respirators seal better and protect the eyes. Fitting and inspection is essential to effectiveness. [8]

Powered air-purifying respirators (PAPRs)

PAPRs are masks with a electricity-powered blower that blows air through a filter to the wearer. Because they create positive pressure, they need not be tightly-fitted. [9] PAPRs typically do not filter exhaust from the wearer. [10]

Exhalation valves

Filtering facepiece half mask with exhalation valve (class: FFP3) Atemluftfilter Einwegmaske.jpg
Filtering facepiece half mask with exhalation valve (class: FFP3)

Some masks have valves, [11] which let exhaled air out unfiltered. This makes them useless for source protection (protecting others against infection by the wearer's breath). [8] It may, however, reduce inwards leakage and thus improve wearer protection. [11]

Unfiltered-exhalation valves are sometimes found in both filtering facepiece [11] and elastomeric respirators; [8] PAPRs cannot by nature ever filter exhaled air, [10] and can never be used for source control.[ citation needed ] They are not generally designed for healthcare use, as of 2017. [12] During the COVID-19 pandemic, masks with unfiltered-exhalation valves did not meet the requirements of some mandatory mask orders. [13] [14]

Filtration standards

U.S. standards (N95 and others)

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 as of 2011: [15]

A video describing N95 certification testing
Oil resistanceRatingDescription
Not oil resistantN95Filters at least 95% of airborne particles
N99Filters at least 99% of airborne particles
N100Filters at least 99.97% of airborne particles
Oil resistantR95Filters at least 95% of airborne particles
R99Filters at least 99% of airborne particles
R100Filters at least 99.97% of airborne particles
Oil proofP95Filters at least 95% of airborne particles
P99Filters at least 99% of airborne particles
P100Filters at least 99.97% of airborne particles

European standards (FFP2 and others)

FFP2 masks 2009Julija-210.jpg
FFP2 masks

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 face pieces" (FFP), that is respirators that are entirely or substantially constructed of filtering material: [16]

ClassFilter TypeFilter penetration limit (at 95 L/min air flow)Inward leakageTypical Elastic Band
FFP1MaskFilters at least 80% of airborne particles<22%Yellow
FFP2Filters at least 94% of airborne particles<8%Blue or White
FFP3Filters at least 99% of airborne particles<2%Red
P1AttachmentFilters at least 80% of airborne particlesN/AN/A
P2Filters at least 94% of airborne particles
P3Filters at least 99.95% of airborne particles

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 and −30 °C 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. [17] (§ 8.5)

Other standards (KN95 and others)

Chinese standard for respirators GB2626-2006.pdf
Chinese standard for respirators

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)": [18]

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: [22] [23]

Disinfection and reuse

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. [11] 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; [11] In the COVID-19 epidemic, 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. [24] Some hospitals have been stockpiling used masks as a precaution. [25] 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"). [26]

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. [11] Fit and comfort do not seem to be harmed by UVGI, moist heat incubation, and microwave-generated steam. [11]

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, and treating with 70% isopropyl alcohol, and hydrogen peroxide gas plasma [11] (made under a vacuum with radio waves [27] ). 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. [11]

UVGI (an ultraviolet method), ethylene oxide, dry oven heating and (highly toxic[ citation needed ]) vaporized hydrogen peroxide are currently the most-favoured methods in use in hospitals, but none have been properly tested. [11] Where enough masks are available, cycling them and reusing a mask only after letting it sit unused for 5 days is preferred. [24]

Related Research Articles

Personal protective equipment Equipment designed to help protect an individual from hazards

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.

Surgical mask Mouth and nose cover against bacterial aerosols

A surgical mask, also known as a face mask, is intended to be worn by health professionals during healthcare procedures. It is designed to prevent infections in patients and treating personnel by catching bacteria shed in liquid droplets and aerosols from the wearer's mouth and nose. They are not designed to protect the wearer from breathing in airborne bacteria or viruses whose particles are smaller. With respect to some infections like influenza they appear as effective as respirators, such as N95 or FFP masks; though the latter provide better protection in laboratory experiments due to their material, shape and tight seal.

Respirator Device worn to protect the user from inhaling contaminants

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 microorganisms. There are two main categories: 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.

Air purifier device to remove contaminants from the air

An air purifier or air cleaner is a device which removes contaminants from the air in a room to improve indoor air quality. These devices are commonly marketed as being beneficial to allergy sufferers and asthmatics, and at reducing or eliminating second-hand tobacco smoke. The commercially graded air purifiers are manufactured as either small stand-alone units or larger units that can be affixed to an air handler unit (AHU) or to an HVAC unit found in the medical, industrial, and commercial industries. Air purifiers may also be used in industry to remove impurities from air before processing. Pressure swing adsorbers or other adsorption techniques are typically used for this.

Immediately dangerous to life or health exposure to dangerous levels of 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."

Dust mask A pad held over the nose and mouth to protect against dust

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.

Respirator fit test

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.

Respirator cartridge container that cleans pollution from air inhaled through it

A respirator cartridge or canister is a container that cleans pollution from air. If the air in the workplace is polluted with fine particulate matter or noxious gases, but contains sufficient oxygen, people working in the polluted air often use air-purifying respirators (APR) to partly protect them. These elastomeric respirators provide users breathable air by removing pollution from ambient air using canisters or cartridges. There are cartridges of different types, and they must be chosen correctly and replaced in a timely manner.

The National Personal Protective Technology Laboratory (NPPTL) is a research center within the National Institute for Occupational Safety and Health located in Pittsburgh, Pennsylvania, specifically devoted towards the research of 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.

NIOSH air filtration rating U.S. rating of respirators such as face masks

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 dust and liquid droplets 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.

Powered air-purifying respirator full-face respirator that provides filtered air to the wearer using an electric fan

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.

Respirator assigned protection factors factors

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.

Workplace respirator testing Testing of respirators in real life conditions

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.

N95 mask Particulate mask that meets the N95 standard of the United States National Institute for Occupational Safety and Health (NIOSH)

An N95 mask or 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. 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.

Workplace hazard controls for COVID-19 Prevention measures for COVID-19

Hazard controls for COVID-19 in US workplaces are the application of occupational safety and health methodologies for hazard controls to the prevention of coronavirus disease 2019 (COVID-19). The proper hazard controls in the workplace depend on the worksite and job task, based on an occupational risk assessment of sources of exposure, disease severity in the community, and risk factors of individual workers who may be vulnerable to contracting COVID-19.

Cloth face mask mask made of common textiles worn over the mouth and nose

A cloth face mask is a mask made of common textiles, usually cotton, worn over the mouth and nose. When more effective masks are not available, and when physical distancing is impossible, cloth face masks are recommended by public health agencies for disease "source control" in epidemic situations to protect others from virus laden droplets in infected mask wearers' breath, coughs, and sneezes. Because they are less effective than N95 masks, surgical masks, or physical distancing in protecting the wearer against viruses, they are not considered to be personal protective equipment by public health agencies. They are used by the general public in household and community settings as perceived protection against both infectious diseases and particulate air pollution.

An FFP mask is a type of protective mask certified by the European Union that serves to protect against particulates such as dust particles. The EN 149 standard defines three classes of filter efficiency for these masks, namely FFP1, FFP2 and FFP3. It is an example of a mechanical filter respirator.

Face masks during the COVID-19 pandemic Use of face coverings during the COVID-19 pandemic

During the COVID-19 pandemic, face masks have been employed as a public and personal health control measure against the spread of SARS-CoV-2. Their use is intended as personal protection to prevent infection and as source control to limit transmission of the virus in a community or healthcare setting. The use of masks has received varying recommendations from different public health agencies and governments. The World Health Organization and other public health organisations agree that masks can limit the spread of respiratory viral diseases such as COVID-19. However, the topic has been a subject of debate, with some public health agencies and governments initially disagreeing on a protocol for wearing face masks.

Source control (respiratory disease) A strategy for reducing disease transmission

Source control is a strategy for reducing disease transmission by blocking respiratory secretions produced through speaking, coughing, or sneezing. 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.

Elastomeric respirator

Elastomeric respirators are a type of air-purifying respirator, consisting of a reusable mask that seals to the face, with exchangeable filters. Elastomeric respirators can be used with chemical cartridge filters that remove gases, mechanical filters that retain particulate matter, or both. As particulate filters, they are comparable or possibly superior to filtering facepiece respirators.

References

  1. ↑ Wei, Neo Kang (6 May 2019). "What is PM0.3 and Why Is It Important?". Smart Air Filters.
  2. 1 2 3 4 5 TSI Incorporated. "Mechanisms of Filtration for High Efficiency Fibrous Filters - Application Note ITI-041" (PDF). Retrieved 29 April 2020.
  3. ↑ Quan, Fu-Shi; Rubino, Ilaria; Lee, Su-Hwa; Koch, Brendan; Choi, Hyo-Jick (2017-01-04). "Universal and reusable virus deactivation system for respiratory protection". Scientific Reports. 7 (1): 1–10. doi:10.1038/srep39956. ISSN   2045-2322.
  4. 1 2 "Standard for Dust Mask". JICOSH Home.
  5. ↑ Guidance for Filtration and Air-Cleaning Systems to Protect Building Environments from Airborne Chemical, Biological, or Radiological Attacks (PDF). Cincinnati, OH: National Institute for Occupational Safety and Health. April 2003. pp. 8–12. doi:10.26616/NIOSHPUB2003136 . Retrieved February 9, 2020.
  6. ↑ "Respirator Trusted-Source Information: What are they?". U.S. National Institute for Occupational Safety and Health. 2018-01-29. Retrieved 2020-03-27.
  7. ↑ Bach, Michael. "Understanding respiratory protection options in Healthcare: The Overlooked Elastomeric". NIOSH Science Blog. CDC.
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  9. ↑ Boškoski, Ivo; Gallo, Camilla; Wallace, Michael B.; Costamagna, Guido (27 April 2020). "COVID-19 pandemic and personal protective equipment shortage: protective efficacy comparing masks and scientific methods for respirator reuse". Gastrointestinal Endoscopy. doi:10.1016/j.gie.2020.04.048. ISSN   0016-5107. PMC   7184993 .
  10. 1 2 The Use and Effectiveness of Powered Air Purifying Respirators in Health Care: Workshop Summary. 2. Defining PAPRs and Current Standards. NCBI. National Academies Press (US). 7 May 2015.
  11. 1 2 3 4 5 6 7 8 9 10 Godoy, Laura R. Garcia; Jones, Amy E.; Anderson, Taylor N.; Fisher, Cameron L.; Seeley, Kylie M. L.; Beeson, Erynn A.; Zane, Hannah K.; Peterson, Jaime W.; Sullivan, Peter D. (1 May 2020). "Facial protection for healthcare workers during pandemics: a scoping review". BMJ Global Health. 5 (5): e002553. doi:10.1136/bmjgh-2020-002553. ISSN   2059-7908. PMC   7228486 . PMID   32371574 . Retrieved 8 May 2020.
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  13. ↑ Wilson, Mark (4/28/2020). "What is a mask valve, and why are cities banning them?". www.msn.com.Check date values in: |date= (help)
  14. ↑ Webeck, Evan (22 April 2020). "Coronavirus: Bay Area mask order takes effect Wednesday. Here's what you need to know". The Mercury News.
  15. ↑ Metzler, R; Szalajda, J (2011). "NIOSH Fact Sheet: NIOSH Approval Labels - Key Information to Protect Yourself" (PDF). DHHS (NIOSH) Publication No. 2011-179. ISSN   0343-6993.
  16. ↑ "Fiche pratique de sécurité ED 105. Appareils de protection respiratoire et métiers de la santé" (pdf). inrs.fr. INRS . Retrieved 7 April 2020.
  17. ↑ "NF EN 149+A1". www.boutique.afnor.org. September 2009. alternative source
  18. ↑ "Technical Bulletin: Comparison of FFP2, KN95, and N95 and Other Filtering Facepiece Respirator Classes" (PDF). 3M Personal Safety Division. January 2020.
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