Wikipedia

Respirator

An N95 filtering facepiece respirator. This kind of respirator is intended to be discarded after being used.
A half-face elastomeric air-purifying respirator. This kind of respirator is reusable, with the filters being replaced periodically.

A respirator is a device designed to protect the wearer from inhaling hazardous atmospheres, including particulate matter such as dusts and airborne microorganisms, as well as hazardous fumes, vapours and gases. 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-purifying respirators range from relatively inexpensive single-use, disposable face masks sometimes referred to as a dust mask to more robust reusable models with replaceable cartridges often called a gas mask.

Physical form [ edit ]

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.

All respirators have some type of facepiece held to the wearer's head with straps, a cloth harness, or some other method. Facepieces come in many different styles and sizes, to accommodate all types of face shapes. The differences in respirator design impact the respirator assigned protection factors, i.e. the resulting degree of protection which kind of hazard.[citation needed]

There are three categories of particulate respirators: particulate filtering facepiece respirators are discarded when they become unsuitable for further use due to considerations of hygiene, excessive resistance, or physical damage; Elastomeric respirators are reusable because the facepiece is cleaned and reused, but the filter cartridges are discarded and replaced when they become unsuitable for further use; and powered air-purifying respirators have a battery-powered blower that moves the airflow through the filters.[1]

Respirators can also have half-face forms that covers the bottom half of the face including the nose and mouth, and full-face forms that cover the entire face. Half-face respirators can only be worn in environments where the contaminants are not toxic to the eyes or facial area. For example, someone who is painting an object with spray paint could wear a half-face respirator, but someone who works with chlorine gas would have to wear a full-face respirator.

Types of filtration [ edit ]

Air-purifying [ edit ]

Protective P100 filter mask worn by NYPD officer

Air-purifying respirators are used against particulates, gases, and vapors that are at atmospheric concentrations less than immediately dangerous to life and health. This includes:

Full hood, half- or full-facepiece designs are marketed in many varieties depending on the hazard of concern using an air filter which acts passively on air inhaled by the wearer. Two common examples of this type of respirator are single-use escape hoods and filter masks. The latter are typically simple, light, single-piece, half-face masks and employ the first three mechanical filter mechanisms in the list below to remove particulates from the air stream. The most common of these is the disposable white N95 variety. It is discarded after single use or some extended period depending on the contaminant. Filter masks also come in replaceable-cartridge, multiple-use models. Typically one or two cartridges attach securely to a mask which has built into it a corresponding number of valves for inhalation and one for exhalation.[citation needed]

The American National Standards Institute (ANSI) and the International Safety Equipment Association (ISEA) established the American National Standard for Air-Purifying Respiratory Protective Smoke Escape Devices to define both test criteria and approval methods for fire/smoke escape hoods. ANSI/ISEA Standard 110 provides design guidance to manufacturers of Respiratory Protective Smoke Escape Devices (RPED) in the form of performance requirements and testing procedures. The standard covers certification, ISO registration for the manufacturer, associated test methods, labeling, conditioning requirements, independent process and quality control audits, and follow-up inspection programs.[2] ANSI/ISEA 110 was prepared by members of the ISEA RPED group, in consultation with testing laboratories and was reviewed by a consensus panel representing users, health and safety professionals and government representatives.[citation needed] The U.S. Consumer Product Safety Commission uses ANSI/ISEA 110 as the benchmark in their testing of fire escape masks.[citation needed]

Mechanical filter [ edit ]

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.[citation needed]

Filtering half mask with exhalation valve (class: FFP3)

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. 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
  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
  4. by using certain resins, waxes, and plastics as coatings on the filter material to attract particles with an electrostatic charge that holds them on the filter surface;
  5. by using gravity and allowing particles to settle into the filter material (this effect is typically negligible); and
  6. by using the particles themselves, after the filter has been used, to act as a filter medium for other particles.

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.[citation needed]

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]

A substantial advance in mechanical filter technology was[when?] the HEPA filter. A HEPA filter can remove as much as 99.97% of all airborne particulates with aerodynamic diameter of 0.3 μm, particles both smaller and larger are removed with an efficiency >99.97%.[3]

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:[4]

A video describing N95 certification testing
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

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::[citation needed]

Class Filter penetration limit (at 95 L/min air flow) Inward leakage
P1 Filters at least 80% of airborne particles N/A
P2 Filters at least 94% of airborne particles N/A
P3 Filters at least 99.95% of airborne particles N/A
FFP1 Filters at least 80% of airborne particles <22%
FFP2 Filters at least 94% of airborne particles <8%
FFP3 Filters at least 99% of airborne particles <2%

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 ten human subjects perform 5 exercises each and for 8 individuals the average measured inward leakage must not exceed 22%, 8% and 2% respectively, as listed above.[citation needed]

Chemical cartridge [ edit ]

Combined gas and particulate respirator filter for protection against acid gases, the type of BKF (БКФ). It has transparent body and special sorbent that changes color after the saturation. This color change may be used for timely replacement of respirators' filters (like End of Service Life Indicator ESLI).

Chemical cartridge respirators use a cartridge to remove gases, volatile organic compounds (VOCs), and other vapors from breathing air by adsorption, absorption, or chemisorption. A typical organic vapor respirator cartridge is a metal or plastic case containing from 25 to 40 grams of sorption media such as activated charcoal or certain resins. The service life of the cartridge varies based, among other variables, on the carbon weight and molecular weight of the vapor and the cartridge media, the concentration of vapor in the atmosphere, the relative humidity of the atmosphere, and the breathing rate of the respirator wearer. When filter cartridges become saturated[disambiguation needed] or particulate accumulation within them begins to restrict air flow, they must be changed.[5]

If the concentration of harmful gases is immediately dangerous to life or health, in workplaces covered by the Occupational Safety and Health Act the US Occupational Safety and Health Administration specifies the use of air-supplied respirators except when intended solely for escape during emergencies.[6] NIOSH also discourages their use under such conditions.[7]

Powered air-purifying respirators [ edit ]

Powered air-purifying respirator (PAPRs) take contaminated air, remove a certain quantity of pollutants and return the air to the user. There are different units for different environments. The units consist of a powered fan which forces incoming air through one or more filters to the user for breathing. The fan and filters may be carried by the user or they may be remotely mounted and the user breathes the air through tubing.[citation needed]

The filter type must be matched to the contaminants that need to be removed. Some PAPR's are designed to remove fine particulate matter, while others are suitable for working with volatile organic compounds as those in spray paints. These must have their filter elements replaced more often than a particulate filter.[citation needed]

Self-contained breathing apparatus (SCBA) [ edit ]

A self contained breathing apparatus (SCBA) typically has three main components: a high-pressure air cylinder (e.g., 2200 psi to 4500 psi), a pressure gauge and regulator, and an inhalation connection (mouthpiece, mouth mask or full face mask), connected together and mounted to a carrying frame or a harness with adjustable shoulder straps and belt so it can be worn on the back. There are two kinds of SCBA: open circuit and closed circuit. Most modern SCBAs are open-circuit.[citation needed]

Open-circuit industrial breathing sets are filled with filtered, compressed air. The compressed air passes through a regulator, is inhaled and exhaled out of the circuit, quickly depleting the supply of air. Air cylinders are made of aluminum, steel, or of a composite construction like fiberglass-wrapped aluminum. The "positive pressure" type is common, which supplies a steady stream of air to stop fumes or smoke from leaking into the mask. Other SCBA's are of the "demand" type, which only supply air when the regulator senses the user inhaling. All fire departments and those working in toxic environments use the positive pressure SCBA for safety reasons.[citation needed]

The closed-circuit type SCBA filters, supplements, and recirculates exhaled gas like a rebreather. It is used when a longer-duration supply of breathing gas is needed, such as in mine rescue and in long tunnels, and going through passages too narrow for a large open-circuit air cylinder.[citation needed]

Industries using respirators [ edit ]

A wide range of industries use respirators including healthcare & pharmaceuticals, defense & public safety services (defense, firefighting & law enforcement), oil and gas industries, manufacturing (automotive, chemical, metal fabrication, food and beverage, wood working, paper and pulp), mining, construction, agriculture and forestry, cement production, power generation, shipbuilding and the textile industry.[8]

Correct usage [ edit ]

Workplace protection factor (PF) of filtering facepiece, measured in real time with two optical dust meters. In-facepiece dust concentration is changed dozens of times in a matter of minutes due to changes of the size of the gaps between the mask and face. Source[9]

A U.S. Department of Labor study[10] showed that in almost 40 thousand American enterprises, the requirements for the correct use of respirators are not always met.

Experts note that in practice it is difficult to achieve elimination of occupational morbidity with the help of respirators:

It is well known how ineffective ... trying to compensate the harmful workplace conditions with ... the use of respirators by employees.[11]

Unfortunately, the only certain way of reducing the exceedance fraction to zero is to ensure that Co (note: Co - concentration of pollutants in the breathing zone) never exceeds the PEL value.[12]

The very limited field tests of air-purifying respirator performance in the workplace show that respirators may perform far less well under actual use conditions than is indicated by laboratory fit factors. We are not yet able to predict the level of protection accurately; it will vary from person to person, and it may also vary from one use to the next for the same individual. In contrast, we can predict the effectiveness of engineering controls, and we can monitor their performance with commercially available state-of-the-art devices.[13]

Fit testing [ edit ]

Most types of respirators depend upon forming a good seal between the respirator body and the face of the wearer. Fit testing procedures have been developed to ensure that the respirator is appropriate for the wearer and the wearer's donning technique is capable of creating an adequate seal.[14] Poor fit can have a negative impact on the respirator's overall filtering effectiveness by as much as 65%.[15] A study on respirator effectiveness conducted in Beijing found that facial fit was the primary contributor to total inward leakage (TIL), based on a test of nine different models.[16] A high-quality respirator should see TIL of only around 5%.[17] Facial hair such as a beard can interfere with proper fit.[18]

Qualitative fit testing typically subjects the wearer to an atmosphere containing an aerosol that can be detected by the wearer, such as saccharin or isoamyl acetate, with the wearer reporting whether detectable levels of the aerosol has penetrated into the breathing area. Quantitative fit testing typically uses a specially prepared respirator with an inserted probe. The respirator is donned, and aerosol concentrations inside and outside of the mask are compared and used to determine a numerical fit factor. Typical room atmosphere contains sufficient particulates to perform the test, but aerosol generators can be used to improve the test accuracy

Contrast with surgical mask [ edit ]

A table listing the attributes of surgical masks and N95 respirators in eight categories
An infographic on the difference between surgical masks and N95 respirators

A surgical mask is a loose-fitting, disposable device that creates a physical barrier between the mouth and nose of the wearer and potential contaminants in the immediate environment. If worn properly, a surgical mask is meant to help block large-particle droplets, splashes, sprays, or splatter that may contain viruses and bacteria. Surgical masks may also help reduce exposure of the wearer's saliva and respiratory secretions to others.[19]

A surgical mask, by design, does not filter or block very small particles in the air that may be transmitted by coughs, sneezes, or certain medical procedures. Surgical masks also do not provide complete protection from germs and other contaminants because of the loose fit between the surface of the face mask and the face.[19] Collection efficiency of surgical mask filters can range from less than 10% to nearly 90% for different manufacturers’ masks when measured using the test parameters for NIOSH certification. However, a study found that even for surgical masks with "good" filters, 80–100% of subjects failed an OSHA-accepted qualitative fit test, and a quantitative test showed 12–25% leakage.[20]

The U.S. Centers for Disease Control and Prevention (CDC) recommends surgical masks in procedures where there can be an aerosol generation from the wearer, if small aerosols can produce a disease to the patient.[21] The CDC recommends the use of respirators with at least N95 certification to protect the wearer from inhalation of infectious particles including Mycobacterium tuberculosis, avian influenza, severe acute respiratory syndrome (SARS), pandemic influenza, and Ebola.[22] Some N95 respirators have been also cleared by the U.S. Food and Drug Administration as surgical are labeled "Surgical N95", and provide respiratory protection to the wearer as well.[23]

Regulation [ edit ]

The choice and use of respirators in developed countries is regulated by national legislation. To ensure that employers choose respirators correctly, and perform high-quality respiratory protection programs, various guides and textbooks have been developed:

History [ edit ]

Earliest records to 19th century [ edit ]

The history of protective respiratory equipment can be traced back as far as the first century, when Pliny the Elder (circa A.D. 23-79) described using animal bladder skins to protect workers in Roman mines from red lead oxide dust.[50] In the 16th century, Leonardo da Vinci suggested that a finely woven cloth dipped in water could protect sailors from a toxic weapon made of powder that he had designed.[51]

In 1785, Jean-François Pilâtre de Rozier invented a respirator.

Alexander von Humboldt introduced a primitive respirator in 1799 when he worked as a mining engineer in Prussia.[52] Practically all respirators in the early 18th century consisted of a bag placed completely over the head, fastened around the throat with windows through which the wearer could see. Some were rubber, some were made of rubberized fabric, and still others of impregnated fabric, but in most cases a tank of compressed air or a reservoir of air under slight pressure was carried by the wearer to supply the necessary breathing air. In some devices certain means were provided for the adsorption of carbon dioxide in exhaled air and the rebreathing of the same air many times; in other cases valves allowed exhalation of used air.[citation needed]

Woodcut of Stenhouse's mask
"How a Man may Breath Safely in a Poisonous Atmosphere", an apparatus providing oxygen while using caustic soda to absorb carbon dioxide, 1909

In 1848, the first US patent for an air purifying respirator was granted to Lewis P. Haslett[53] for his 'Haslett's Lung Protector,' which filtered dust from the air using one-way clapper valves and a filter made of moistened wool or a similar porous substance. Following Haslett, a long string of patents were issued for air purifying devices, including patents for the use of cotton fibers as a filtering medium, for charcoal and lime absorption of poisonous vapors, and for improvements on the eyepiece and eyepiece assembly.[citation needed] Hutson Hurd patented a cup-shaped mask in 1879 which became widespread in industrial use, and Hurd's H.S. Cover Company was still in business in the 1970s.[54]

Inventors in Europe included John Stenhouse, a Scottish chemist, who investigated the power of charcoal in its various forms, to capture and hold large volumes of gas. He built one of the first respirators able to remove toxic gases from the air, paving the way for activated charcoal to become the most widely used filter for respirators.[55] British physicist John Tyndall took Stenhouse's mask, added a filter of cotton wool saturated with lime, glycerin, and charcoal, and in 1871 invented a 'fireman's respirator', a hood that filtered smoke and gas from air, which he exhibited at a meeting of the Royal Society in London in 1874.[56] Also in 1874, Samuel Barton patented a device that 'permitted respiration in places where the atmosphere is charged with noxious gases, or vapors, smoke, or other impurities.'[57] German Bernhard Loeb patented several inventions to 'purify foul or vitiated air,' and counted the Brooklyn Fire Department among his customers.[citation needed]

World War I [ edit ]

The first recorded response and defense against chemical attacks using respirators occurred during the Second Battle of Ypres on the Western Front in World War I. It was the first time Germany used chemical weapons on a large scale releasing 168 tons of chlorine gas over a four-mile (6 km) front killing around 6,000 troops within ten minutes through asphyxiation. The gas being denser than air flowed downwards forcing troops to climb out of their trenches. Reserve Canadian troops, who were away from the attack, used urine-soaked cloths as primitive respirators. A Canadian soldier realized that the ammonia in urine would react with the chlorine, neutralizing it, and that the water would dissolve the chlorine, allowing soldiers to breathe through the gas.[citation needed]

21st century [ edit ]

China normally makes 10 million masks per day, about half of the world production. During the 2019–20 coronavirus pandemic, 2,500 factories were converted to produce 116 million daily.[58]

See also [ edit ]

References [ edit ]

  1. ^ "Respirator Trusted-Source Information: What are they?". U.S. National Institute for Occupational Safety and Health. 29 January 2018. Retrieved 27 March 2020.
  2. ^ "International Safety Equipment Association". Safetyequipment.org. Retrieved 18 April 2010.
  3. ^ 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 9 February 2020.
  4. ^ 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.
  5. ^ The document describes the methods used previously and currently used to perform the timely replacement of cartridges in air purifying respirators.
  6. ^ OSHA standard 29 CFR 1910.134 "Respiratory Protection"
  7. ^ Bollinger, Nancy; et al. (2004). NIOSH Respirator Selection Logic. DHHS (NIOSH) Publication No. 2005-100. Cincinnati, Ohio: National Institute for Occupational Safety and Health. p. 32. doi:10.26616/NIOSHPUB2005100.
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  12. ^ M. Nicas & R. Spear (1992). "A Probability Model for Assessing Exposure among Respirator Wearers: Part II - Overexposure to Chronic versus Acute Toxicants". American Industrial Hygiene Association Journal. 53 (7): 419–426. doi:10.1080/15298669291359889. PMID 1496932. Retrieved 22 January 2018.
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  18. ^ "To Beard or not to Beard? That's a good Question! | | Blogs | CDC". Retrieved 27 February 2020.
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Bibliography [ edit ]

Further reading

External links [ edit ]

  • Air-Purifying Respirators (APR): cdc.gov/niosh. Respirator manufacturer approvals for NIOSH-certified air-purifying respirator with CBRN Protections (CBRN APR). This link covers APR and Air-Purifying Escape Respirators (APER) certified by the NIOSH's National Personal Protective Technology Laboratory (NPPTL), Pittsburgh, PA, to CBRN protection NIOSH standards. CBRN APR are tight-fitting, full-face respirators with approved accessories and protect the user breathing zone by relying on user negative pressure, fit testing and user seal checks to filter less than Immediately Dangerous to Life and Health (IDLH) concentrations of hazardous respiratory compounds and particulates through NIOSH CBRN Cap 1, Cap 2 or Cap 3 canisters for CBRN APR- or CBRN 15- or CBRN 30-rated APER.
  • PAPR: cdc.gov/niosh. Respirator manufacturer approvals for NIOSH-certified powered air-purifying respirator with CBRN Protections (CBRN PAPR-loose fitting or tight fitting)
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