respirator A respirator is a device designed to protect the wearer from inhaling hazardous atmospheres including lead, lead fumes, vapors, gases and particulate matter such as dusts and airborne pathogens such as viruses. There are two main categories o ...

cartridge or

gas mask A gas mask is a piece 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 ...

canister is a type of filter that removes gases,

volatile organic compound Volatile organic compounds (VOCs) are organic compounds that have a high vapor pressure at room temperature. They are common and exist in a variety of settings and products, not limited to Indoor mold, house mold, Upholstery, upholstered furnitur ...

s (VOCs), and other vapors from the air through

adsorption Adsorption is the adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface. This process creates a film of the ''adsorbate'' on the surface of the ''adsorbent''. This process differs from absorption, in which a ...

absorption Absorption may refer to: Chemistry and biology *Absorption (biology), digestion **Absorption (small intestine) *Absorption (chemistry), diffusion of particles of gas or liquid into liquid or solid materials *Absorption (skin), a route by which su ...

, or

chemisorption Chemisorption is a kind of adsorption which involves a chemical reaction between the surface and the adsorbate. New chemical bonds are generated at the adsorbent surface. Examples include macroscopic phenomena that can be very obvious, like co ...

. It is one of two basic types of filters used by air-purifying respirators. The other is a

mechanical filter A mechanical filter is a signal processing filter usually used in place of an electronic filter at radio frequencies. Its purpose is the same as that of a normal electronic filter: to pass a range of signal frequencies, but to block others. ...

, which removes only

particulates Particulate matter (PM) or particulates are microscopic particles of solid or liquid matter suspension (chemistry), suspended in the atmosphere of Earth, air. An ''aerosol'' is a mixture of particulates and air, as opposed to the particulate ...

. Hybrid filters combine the two.

Workplace A workplace is a location where someone works, for their employer or themselves, a place of employment. Such a place can range from a home office to a large office building or factory. For industrialized societies, the workplace is one of the ...

air that is polluted with fine

particulate matter Particulate matter (PM) or particulates are microscopic particles of solid or liquid matter suspended in the air. An ''aerosol'' is a mixture of particulates and air, as opposed to the particulate matter alone, though it is sometimes defin ...

or noxious gases but that contains enough oxygen (in the US, this is ruled to be a concentration above 19.5%; in the Russian Federation, above 18%), can be rendered safe via air-purifying respirators. Cartridges are of different types, and must be chosen correctly and replaced on an appropriate schedule.

Purification methods

Absorption

Capturing noxious gases may be accomplished by

sorbent A sorbent is an insoluble material that either absorbs or adsorbs liquids or gases. They are frequently used to remove pollutants and in the cleanup of chemical accidents and oil spills. Besides their uses in industry, sorbents are used in comm ...

s. These materials (

activated carbon Activated carbon, also called activated charcoal, is a form of carbon commonly used to filter contaminants from water and air, among many other uses. It is processed (activated) to have small, low-volume pores that greatly increase the surface ar ...

, ,

zeolite Zeolites are a group of several microporous, crystalline aluminosilicate minerals commonly used as commercial adsorbents and catalysts. They mainly consist of silicon, aluminium, oxygen, and have the general formula ･y where is either a meta ...

, etc.) have a large

specific surface area Specific surface area (SSA) is a property of solids defined as the total surface area (SA) of a material per unit mass, (with units of m2/kg or m2/g). Alternatively, it may be defined as SA per solid or bulk volume (units of m2/m3 or m−1). I ...

and can absorb many gases. Typically, such sorbents are in the form of granules and fill the cartridge. Contaminated air travels through the cartridge's bed of sorbent granules. Movable harmful gas

molecule A molecule is a group of two or more atoms that are held together by Force, attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemi ...

s collide with the surface of the sorbent and remain therein. The sorbent gradually saturates and loses its ability to capture pollutants. The bond strength between captured molecules and the sorbent is small, and molecules can separate from the sorbent and return to the air. The sorbent's ability to capture gases depends on the properties of the gases and their concentrations, including air

temperature Temperature is a physical quantity that quantitatively expresses the attribute of hotness or coldness. Temperature is measurement, measured with a thermometer. It reflects the average kinetic energy of the vibrating and colliding atoms making ...

and

relative humidity Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation (meteorology), precipitation, dew, or fog t ...

.Conference listing
/ref>

Chemisorption

Chemisorption Chemisorption is a kind of adsorption which involves a chemical reaction between the surface and the adsorbate. New chemical bonds are generated at the adsorbent surface. Examples include macroscopic phenomena that can be very obvious, like co ...

utilizes a chemical reaction between the gas and the absorber. The ability of some harmful gases to react chemically with other substances can be used to capture them. Creating strong links between gas molecules and a sorbent may allow repeated use of a canister if it has enough unsaturated sorbent.

Copper Copper is a chemical element; it has symbol Cu (from Latin ) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orang ...

salts, for example, can form complex compounds with ammonia. A mixture of copper ions (+2),

zinc carbonate Zinc carbonate is the inorganic compound with the formula ZnCO3. It is a white solid that is insoluble in water. It exists in nature as the mineral smithsonite. It is prepared by treating cold solutions of zinc sulfate with potassium bicarbonat ...

, and TEDA can detoxify

hydrogen cyanide Hydrogen cyanide (formerly known as prussic acid) is a chemical compound with the chemical formula, formula HCN and structural formula . It is a highly toxic and flammable liquid that boiling, boils slightly above room temperature, at . HCN is ...

. By saturating

with chemicals, chemisorption can be used to help the material make stronger ties with molecules of trapped gases and improve the capture of harmful gases. Saturation of

iodine Iodine is a chemical element; it has symbol I and atomic number 53. The heaviest of the stable halogens, it exists at standard conditions as a semi-lustrous, non-metallic solid that melts to form a deep violet liquid at , and boils to a vi ...

improves mercury capture, saturation of metal

salts In chemistry, a salt or ionic compound is a chemical compound consisting of an assembly of positively charged ions ( cations) and negatively charged ions (anions), which results in a compound with no net electric charge (electrically neutral). ...

improves

ammonia Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...

capture, and saturation of metal

oxide An oxide () is a chemical compound containing at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion (anion bearing a net charge of −2) of oxygen, an O2− ion with oxygen in the oxidation st ...

s improves

acid gas Acid gas is a particular typology of natural gas or any other gas mixture containing significant quantities of hydrogen sulfide (H2S), carbon dioxide (CO2), or similar acidic gases. A gas is determined to be acidic or not after it is mixed with wat ...

capture.

Catalytic decomposition

Some harmful gases can be neutralized through

catalytic oxidation Catalytic oxidation are processes that rely on catalysts to introduce oxygen into organic and inorganic compounds. Many applications, including the focus of this article, involve oxidation by oxygen. Such processes are conducted on a large scale ...

. A

hopcalite Hopcalite is the trade name for a number of mixtures that mainly consist of oxides of copper and manganese, which are used as catalysts for the conversion of carbon monoxide to carbon dioxide when exposed to the oxygen in the air at room temperatu ...

can oxidize toxic

carbon monoxide Carbon monoxide (chemical formula CO) is a poisonous, flammable gas that is colorless, odorless, tasteless, and slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the si ...

(CO) into harmless

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

(CO₂). The effectiveness of this

catalyst Catalysis () is the increase in rate of a chemical reaction due to an added substance known as a catalyst (). Catalysts are not consumed by the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recycles quick ...

strongly decreases as

increases. Therefore,

desiccant A desiccant is a hygroscopic substance that is used to induce or sustain a state of dryness (desiccation) in its vicinity; it is the opposite of a humectant. Commonly encountered pre-packaged desiccants are solids that absorb water. Desiccant ...

s are often added. Air always contains

water vapor Water vapor, water vapour, or aqueous vapor is the gaseous phase of Properties of water, water. It is one Phase (matter), state of water within the hydrosphere. Water vapor can be produced from the evaporation or boiling of liquid water or from th ...

, and after saturation of the desiccant, the catalyst ceases to function.

Combined cartridges and canisters

Combined, or multi-gas canisters and cartridges, protect from harmful gases by using multiple sorbents or catalysts. An example is ''ASZM-TEDA Carbon'' canister used in

CBRN Chemical, biological, radiological, and nuclear defense (CBRN defense) or Nuclear, biological, and chemical protection (NBC protection) is a class of protective measures taken in situations where chemical, biological, radiological, or nucl ...

masks by the

US Army The United States Army (USA) is the primary land service branch of the United States Department of Defense. It is designated as the Army of the United States in the United States Constitution.Article II, section 2, clause 1 of the United Stat ...

. This is a form of activated carbon saturated with copper, zinc, silver, and molybdenum compounds, as well as with triethylenediamine (TEDA).

Classification and marking

Cartridge selection comes after assessing the atmosphere.

NIOSH The National Institute for Occupational Safety and Health (NIOSH, ) is the United States federal agency responsible for conducting research and making recommendations for the prevention of work-related injury, illness, disability, and death. It ...

guides cartridge (and canister) choice in the US along with manufacturer recommendations.

United States

European Union and Russia

In the

European Union The European Union (EU) is a supranational union, supranational political union, political and economic union of Member state of the European Union, member states that are Geography of the European Union, located primarily in Europe. The u ...

(EU) and the

Russian Federation Russia, or the Russian Federation, is a country spanning Eastern Europe and North Asia. It is the list of countries and dependencies by area, largest country in the world, and extends across Time in Russia, eleven time zones, sharing Borders ...

(RF), manufacturers can certify cartridges intended for cleaning the air of various gaseous contaminants. The codes are covered by EN 14387, additionally, particulate codes P1, P2, and P3 are used. For example, A1P2 is the code for commonly used filters in industry and agriculture that provide protection against A-type gases, commonly occurring particulates, and other organic particulates.

Cartridges AX, SX, and NO do not distinguish on the sorption capacity (as in the US) when they are classified and certified. If the cartridge is designed to protect from several different types of harmful gases, the label will list all designations in order. For example: A2B1, color - brown and grey. Other jurisdictions that use this style of classification include Australia/New Zealand (AS/NZS 1716:2012) and China (GB 2890:2009).

Detection of end of service life

Service lives of all types of cartridges are limited, therefore, the employer is obliged to replace them in a timely manner.

Old methods

Subjective reactions of users' sensory systems

The use of cartridges in the contaminated atmosphere leads to saturation of the sorbent (or the dryer — when using catalysts). The concentration of harmful gases in the purified air gradually increases. The ingress of harmful gases in the inhaled air can lead to a reaction in a user's

sensory system The sensory nervous system is a part of the nervous system responsible for processing sensory information. A sensory system consists of sensory neurons (including the sensory receptor cells), neural pathways, and parts of the brain involved ...

odor An odor (American English) or odour ( Commonwealth English; see spelling differences) is a smell or a scent caused by one or more volatilized chemical compounds generally found in low concentrations that humans and many animals can perceive ...

taste The gustatory system or sense of taste is the sensory system that is partially responsible for the perception of taste. Taste is the perception stimulated when a substance in the mouth biochemistry, reacts chemically with taste receptor cells l ...

irritation Irritation, in biology and physiology, is a state of inflammation or painful reaction to allergy or cell-lining damage. A stimulus or agent which induces the state of irritation is an irritant. Irritants are typically thought of as chemical age ...

of the

respiratory system The respiratory system (also respiratory apparatus, ventilatory system) is a biological system consisting of specific organs and structures used for gas exchange in animals and plants. The anatomy and physiology that make this happen varies grea ...

dizziness Dizziness is an imprecise term that can refer to a sense of disorientation in space, vertigo, or lightheadedness. It can also refer to Balance disorder, disequilibrium or a non-specific feeling, such as giddiness or foolishness. Dizziness is a ...

headaches A headache, also known as cephalalgia, is the symptom of pain in the face, head, or neck. It can occur as a migraine, tension-type headache, or cluster headache. There is an increased risk of depression in those with severe headaches. Head ...

, and other health impairments up to the loss of

consciousness Consciousness, at its simplest, is awareness of a state or object, either internal to oneself or in one's external environment. However, its nature has led to millennia of analyses, explanations, and debate among philosophers, scientists, an ...

. These signs (known in the US as "warning properties" - p. 28) indicate that one must leave the polluted workplace area, and replace the cartridge with a new one. This can also be a symptom of a loose fit the mask to one's

face The face is the front of the head that features the eyes, nose and mouth, and through which animals express many of their emotions. The face is crucial for human identity, and damage such as scarring or developmental deformities may affect th ...

and the leakage of unfiltered air through the gaps between the mask and the face. Historically, this method is the oldest. ESLI-after-Hg-exposure

The advantages of this method – if harmful gases have warning properties at concentrations less than 1 PEL, the replacement will be produced on time (''in most cases, at least''); the application of this method does not require the use of special cartridges (more expensive) and accessories; replacement happens when one needs to do it – after the sorbent saturation, and without any calculations; the sorption capacity of the cartridges is fully expired (which reduces costs for respiratory protection). The disadvantage of this method is that some harmful gases have no warning properties. For example, there is a list of over 500 harmful gases in the Respirator Selection Guide and over 60 of them have no warning properties, and there is no such information for over 100 of them. So, if one uses warning properties to replace cartridges, this may lead to breathing air with an excess harmful gas concentration in some cases. According to the ICHS, all listed substances in the table cannot be reliably detected by smell at dangerous concentrations. On the other hand, all publications with information only about average odor perception thresholds can partly misinform the reader, since they create the impression that the thresholds are stable and constant. If the threshold odor of

Benzene Benzene is an Organic compound, organic chemical compound with the Chemical formula#Molecular formula, molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar hexagonal Ring (chemistry), ring with one hyd ...

is 20 PEL; and if its concentration is only 10 PEL, one cannot timely change cartridges by using smell - they could be "used" forever'', but they cannot protect forever.'' The practice has shown that the presence of warning properties does not always lead to timely cartridge replacement. A study showed that on average 95% of a group of people have an individual threshold of olfactory sensitivity in the range of from 1/16 to 16 from the mean. This means that 2.5% of people will not be able to smell harmful gases at a concentration 16 times greater than the average threshold of perception of a smell. The threshold of sensitivity of different people can vary by two orders of magnitude. That is, 15% of people do not smell at concentrations four times higher than the sensitivity threshold. The value of threshold smell greatly depends on how much

attention Attention or focus, is the concentration of awareness on some phenomenon to the exclusion of other stimuli. It is the selective concentration on discrete information, either subjectively or objectively. William James (1890) wrote that "Atte ...

people pay to it, and on their health status. The sensitivity may be reduced, for example, due to

colds The common cold, or the cold, is a virus, viral infectious disease of the upper respiratory tract that primarily affects the Respiratory epithelium, respiratory mucosa of the human nose, nose, throat, Paranasal sinuses, sinuses, and larynx. ...

and other ailments. It turns out that a worker's ability to detect smell also depends on the nature of the work to be performed — if it requires concentration, a user may not react to the smell. Prolonged exposure to harmful gases (for example,

hydrogen sulfide Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is toxic, corrosive, and flammable. Trace amounts in ambient atmosphere have a characteristic foul odor of rotten eggs. Swedish chemist ...

) at low concentrations can create

olfactory fatigue Olfactory fatigue, also known as odor fatigue, odor habituation, olfactory adaptation, or noseblindness, is the temporary, normal inability to distinguish a particular odor after a prolonged exposure to that airborne compound. For example, when en ...

which reduces sensitivity. In a group of workers, the average styrene odor threshold increased by an order of magnitude due to adaptation. However, the perception of odors of other substances did not change. And the workers could mistakenly believe that their olfactory organ remained sensitive to styrene too. This was the reason for the ban to use this method of cartridge replacement in the US since 1996 (the

Occupational Safety and Health Administration The Occupational Safety and Health Administration (OSHA; ) is a regulatory agency of the United States Department of Labor that originally had federal visitorial powers to inspect and examine workplaces. The United States Congress established ...

OSHA standard).

Mass increase

To protect workers from carbon monoxide cartridges often use the catalyst

. This catalyst does not change its properties over time of use, but when it moistens, the degree of protection may be significantly reduced. Because water vapor is always present in the air, the polluted air is dehumidified in the cartridge (for use of the catalyst). Since the mass of water vapor in the polluted air is greater than the mass of harmful gases, trapping moisture from the air leads to a significantly higher increase in the mass of cartridges than the trapping gases. This is a substantial difference, and it can be used to determine whether to continue to use gas cartridges further without replacement. The cartridge is weighed, and a decision can be made based on the magnitude of increase of its mass. For example, the book describes gas cartridges (model "СО"), which were replaced after a weight gain (relative to initial) of 50 grams.

Other methods

The documents described Soviet cartridges (model "Г"), designed to protect from mercury. Their service life was limited to 100 hours of use (cartridges without particle filter), or 60 hours of use (cartridges with particle filter), after which it was necessary to replace the cartridge with a new one. The documents describe a non-destructive way to determine the remaining service life of new and used gas cartridges. Polluted air was pumped through the cartridge. The degree of purification of air depends on how much-unsaturated sorbent is in the cartridge, therefore, accurate measurement of gas concentration in the cleaned air allows one to estimate the amount of the unsaturated sorbent. Polluted air ( 1-bromobutane) was pumped for a very short time, and therefore, such tests do not reduce the service life considerably. The sorption capacity decreased due to absorption of this gas by about 0.5% of the sorption capacity of a new cartridge. The method was also used for 100%

quality control Quality control (QC) is a process by which entities review the quality of all factors involved in production. ISO 9000 defines quality control as "a part of quality management focused on fulfilling quality requirements". This approach plac ...

of the cartridges manufactured by the English firm Martindale Protection Co. (10 microliters 1-bromobutane injected into the air stream), and to check the cartridges issued to workers in firms Waring, Ltd. and Rentokil, Ltd. This method was used in the Chemical Defence Establishment in the early 1970s. The experts who developed this method received a

patent A patent is a type of intellectual property that gives its owner the legal right to exclude others from making, using, or selling an invention for a limited period of time in exchange for publishing an sufficiency of disclosure, enabling discl ...

. The document briefly describes two methods to objectively evaluate the degree of saturation of the sorbent in the cartridges. It recommends using spectral and microchemical methods. The spectral method is based on determining the presence of harmful substances in the cartridge by sampling, with subsequent analysis on a special device (стилоскоп - ''on Russian''). A microchemical method is based on a layer-by-layer determination of the presence of harmful substances in the sorbent by sampling with subsequent analysis by chemical method. If the air is contaminated with the most toxic substances, the book recommends to limit the further duration of cartridge use, and it recommended to apply the spectral method (

arsine Arsine (IUPAC name: arsane) is an inorganic compound with the formula As H3. This flammable, pyrophoric, and highly toxic pnictogen hydride gas is one of the simplest compounds of arsenic. Despite its lethality, it finds some applications in th ...

and

phosphine Phosphine (IUPAC name: phosphane) is a colorless, flammable, highly toxic compound with the chemical formula , classed as a pnictogen hydride. Pure phosphine is odorless, but technical grade samples have a highly unpleasant odor like rotting ...

phosgene Phosgene is an organic chemical compound with the formula . It is a toxic, colorless gas; in low concentrations, its musty odor resembles that of freshly cut hay or grass. It can be thought of chemically as the double acyl chloride analog of ...

fluorine Fluorine is a chemical element; it has Chemical symbol, symbol F and atomic number 9. It is the lightest halogen and exists at Standard temperature and pressure, standard conditions as pale yellow Diatomic molecule, diatomic gas. Fluorine is extre ...

organochloride Organochlorine chemistry is concerned with the properties of organochlorine compounds, or organochlorides, organic compounds that contain one or more carbon–chlorine bonds. The chloroalkane class (alkanes with one or more hydrogens substituted ...

organometallic compounds Organometallic chemistry is the study of organometallic compounds, chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, including alkali, alkaline earth, and transition metals, an ...

), and microchemical methods (

cyanogen Cyanogen is the chemical compound with the chemical formula, formula . Its structure is . The simplest stable carbon nitride, it is a Transparency and translucency, colorless and highly toxic gas with a pungency, pungent odor. The molecule is a ...

s). Unfortunately, in both cases, there is no description of how to extract a sample of the sorbent from the cartridge housing (the housing is usually not detachable), and use the cartridge after this test, if the test shows that it does not have a lot of saturated sorbents.

Modern methods

Cartridge certification provides a minimum value of their sorption capacity. US

OSHA The Occupational Safety and Health Administration (OSHA; ) is a regulatory agency of the United States Department of Labor that originally had federal visitorial powers to inspect and examine workplaces. The United States Congress established ...

standard for

1,3-Butadiene 1,3-Butadiene () is the organic compound with the formula CH2=CH-CH=CH2. It is a colorless gas that is easily condensed to a liquid. It is important industrially as a precursor to synthetic rubber. The molecule can be viewed as the union of two ...

indicates the specific service life of the cartridges.

Laboratory testing

If the company has a

laboratory A laboratory (; ; colloquially lab) is a facility that provides controlled conditions in which scientific or technological research, experiments, and measurement may be performed. Laboratories are found in a variety of settings such as schools ...

with the right equipment, specialists can skip the contaminated air through the cartridge and determine the degree of cleaning needed. This method enables one to determine the service life in an environment where the air is contaminated with a mixture of different substances that affect their capture with a sorbent (one affecting another capture). Service life calculation methods for such conditions have been developed relatively recently. However, this requires accurate information on concentrations of noxious substances, and they often are not permanent. Tests in laboratories can identify the balance of service life of cartridges after their use. If the remainder is large, similar cartridges in such circumstances can be used over a longer period of time. In some cases, a large balance allows the use of cartridges repeatedly. This method does not require accurate information on the concentrations of harmful substances. The cartridge replacement

schedule A schedule (, ) or a timetable, as a basic time-management tool, consists of a list of times at which possible tasks, events, or actions are intended to take place, or of a sequence of events in the chronological order in which such thing ...

is drawn upon the basis of the results of their testing in the laboratory. This method has a serious drawback. The company must have complex and expensive equipment and trained professionals to use it, which is not always possible. According to a poll, cartridges replacement in the US was carried out on the basis of laboratory tests in approximately 5% of all organizations. Research to determine whether it is possible to calculate the service life of respirator cartridges (if one know the conditions of their use) have been conducted in developed countries since the 1970s. This allows one to replace cartridges in a timely fashion without the use of sophisticated and expensive equipment.

Computer programs

The world's leading respirator manufacturers offered customers

computer program A computer program is a sequence or set of instructions in a programming language for a computer to Execution (computing), execute. It is one component of software, which also includes software documentation, documentation and other intangibl ...

s for calculating the service life already in the year 2000.

3M program allowed to calculate the service life of the cartridges exposed with more than 900 harmful gases and their combinations in 2013. The MSA program enables taking into account hundreds of gases and their combinations. The same program was developed by Scott and Dragerwerk. J. Wood developed a mathematical model and software that now allows one to calculate the service life of any cartridges with known properties. Now OSHA uses it in its Advisor Genius program. The merit of this way of replacing the cartridges is that it allows an employer to use normal, "common" cartridges, and if they have the exact data, they may replace them in time. The downside is that because of air contamination is often not constant, and the nature of the work to be performed is not always stable (that is, the flow of air through the cartridges is not permanent), it is recommended to use working conditions for calculations, equal to the worst case, for reliable protection. However, in all other cases, cartridges will be replaced with a partially used sorbent. This increases the costs of respiratory protection due to more frequent cartridge replacements. In addition, calculation accuracy is reduced under very high

, because the mathematical model does not take into account some of the physical effects in such cases.

End-of-service-life indicators

If a cartridge has a device to warn the user of the approaching expiration of the service life (end-of-service-life indicator, ESLI), the indication can be used for timely replacement of cartridges. ESLI can be active or passive. A passive indicator often uses a sensor that changes color. This element is installed in the cartridge at some distance from the filtered air outlet so that the color change occurs before harmful gases begin to pass through the cartridge. An active indicator may use a light or an audible alarm to signal that a cartridge needs to be replaced. Passive end-of-service-life indicators ESLI-1925.jpg , Yablick 1925 Индикатор для определения срока службы фильтра End of Service Life Indicator ESLI 05.jpg , ChemMotif 2000 Индикатор для определения срока службы фильтра End of Service Life Indicator ESLI 12.jpg , THO 1998 & Linders Индикатор для определения срока службы фильтра End of Service Life Indicator ESLI 14.jpg , ТНО 2004 Индикатор для определения срока службы фильтра End of Service Life Indicator ESLI 06.jpg , Dragerwerk 1986 Индикатор для определения срока службы фильтра End of Service Life Indicator ESLI 15.jpg , Wallace 1975 Индикатор для определения срока службы фильтра End of Service Life Indicator ESLI 16.jpg , Wallace 1975 Индикатор для определения срока службы фильтра End of Service Life Indicator ESLI 17.jpg , Roberts 1976 Индикатор для определения срока службы фильтра End of Service Life Indicator ESLI 18.jpg , China 2001 Индикатор для определения срока службы фильтра End of Service Life Indicator ESLI 19.jpg , Dragerwerk 1957 Active indicators use light or an audible alarm for user notification that is triggered by a sensor that is usually installed in the cartridge. Such indicators allow one to replace the cartridges on time in any light and do not require the worker to pay attention to the color of the indicator. They can also be used by workers who badly distinguish different colors. Active-ESLI

Despite the presence of solutions for technical problems, and the availability of established certification requirements to the ESLI, during the period from 1984 (first certification standard with requirements for active ESLI) until 2013 not one cartridge with active ESLI was approved in the US. It turned out that the requirements for the cartridges are not quite exact, and employers are under no requirement to use these indicators specifically. Therefore, respirator manufacturers fear

commercial failure Failure is the social concept of not meeting a desirable or intended objective, and is usually viewed as the opposite of success. The criteria for failure depends on context, and may be relative to a particular observer or belief system. One ...

when selling new unusual products, although they continue to carry out research and development work in this area. Active end-of-service-life indicators: Индикатор для определения срока службы фильтра End of Service Life Indicator ESLI.jpg , American Optical Индикатор для определения срока службы фильтра End of Service Life Indicator ESLI 02.jpg , Auergesellschaft 1989 Индикатор для определения срока службы фильтра End of Service Life Indicator ESLI 03.jpg , Auergesellschaft 1989 Индикатор для определения срока службы фильтра End of Service Life Indicator ESLI 04.jpg , Bernard 1998 Индикатор для определения срока службы фильтра End of Service Life Indicator ESLI 07.jpg , Dragerwerk 1994 Индикатор для определения срока службы фильтра End of Service Life Indicator ESLI 08.jpg , FOGS 1998 Индикатор для определения срока службы фильтра End of Service Life Indicator ESLI 09.jpg , Geraetebau 1991 Индикатор для определения срока службы фильтра End of Service Life Indicator ESLI 10.jpg , Shigematsu 2002 Индикатор для определения срока службы фильтра End of Service Life Indicator ESLI 11.jpg , Stetter 1991 ESLI 6051i 1-4

Examination of respirator use in the US showed that over 200,000 workers may be exposed to excessive harmful gases due to late replacement of cartridges. So, the Laboratory of PPE ( NPPTL) at the

began to develop an active ESLI. After the completion of the work, its results will help establish clear legal requirements for employers to follow and resulting technology will be transferred to industry to use in new improved RPD.

Legal requirements

Since it is not always possible to replace cartridges in a timely manner through the use of their odor ets,

has banned the use of this method. The employer is obliged to use only two ways to replace cartridges: on schedule, and by using ESLI (because only these methods provide reliable preservation of workers' health). OSHA instructions to inspectors provides specific guidance on inspection of implementation of such requirements. On the other hand, the state requires manufacturers to provide the consumer with all necessary information about cartridges to allow one to make a schedule for their timely replacement. Similar requirements exist in the standard on occupational safety, governing selection and application of RPD in EU. In England a tutorial on the selection and use of respirators recommends obtaining information from the manufacturer, and replacing the cartridges on a schedule or use ESLI, and prohibits reusing cartridges after exposure of volatile substances that can migrate. * The US law required the employer to use exceptionally supplied air RPD (SAR) for protection against harmful gases that have no warning properties. The use of supplied air respirators may be the only way to reliably protect workers in circumstances when there is no ESLI, and it is impossible to calculate their service life. * Legislation in the EU allows an employer to use only supplied air respirators when employees work in conditions where air pollution is

IDLH 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 adver ...

, because of the risk of untimely cartridge replacement. Respirator canister with ESLI for asid gases -9

Reuse

If the cartridge contains a lot of the sorbent and if the concentration of contaminants is low; or if the cartridge was used for a short duration of time, after completion of its use, it still has a lot of unsaturated sorbent (which can capture gases). This may allow using such cartridges again. The molecules of an entrapped gases may de-absorb during storage of the cartridge. Due to the difference of concentrations inside the body of the cartridge (at the inlet concentration is greater; at the outlet for purified air concentration is lesser), these de-absorbed molecules migrate inside the cartridge to the outlet. The study of cartridges exposed to

methyl bromide Bromomethane, commonly known as methyl bromide, is an organobromine compound with chemical formula, formula Carbon, CHydrogen, H3Bromine, Br. This colorless, odorless, nonflammable gas is Bromine cycle, produced both industrially and biologically ...

showed that this migration can impede the re-use of storage. Concentration of harmful substances in the purified air may exceed the PEL (even if clean air is pumped through the cartridge). To protect worker health, US law prohibits cartridge reuse when exposed to harmful substances that can migrate, even if the cartridge has much non-saturated sorbent after the first use. According to the standards, "volatile" substances (those able to migrate) are considered substances with a

boiling point The boiling point of a substance is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapor. The boiling point of a liquid varies depending upon the surrounding envi ...

below 65 °C. But studies have shown that at the boiling point above 65 °C reuse of the cartridge may be unsafe. Therefore, the manufacturer must provide the buyer with all information required for safe cartridge use. So, if the period of continuous service life of the cartridge (calculated by the program - see above) exceeds eight hours (see tables 4 and 5), the legislation may limit their use to one shift. The paper provides a procedure for calculating the concentration of harmful substances in purified air at the start of cartridge reuse which allows one to determine exactly where they may be safely reused. But these scientific results are not yet reflected in any standards or guidelines on respirator use. The author of the article, working in the US, did not even try to consider the use of gas cartridges more than twice. On the author's website, one can download a free computer program that allows one to calculate concentration of harmful substances immediately after the start of re-use of the cartridge (which allows one to determine if it is safe).

Regenerating gas cartridges

Activated carbon does not bond with harmful gases strongly, so they can be released later. Other sorbents undergo chemical reactions with the hazard and form strong bonds. Special technologies have been developed for recovery of used cartridges. They created conditions that have stimulated desorption caught earlier harmful substances. This used

steam Steam is water vapor, often mixed with air or an aerosol of liquid water droplets. This may occur due to evaporation or due to boiling, where heat is applied until water reaches the enthalpy of vaporization. Saturated or superheated steam is inv ...

or heated air in the 1930s or other methods. Processing of the sorbent was carried out after its removal from the body of the cartridge, or without removing. Specialists tried to use

ion-exchange resin An ion-exchange resin or ion-exchange polymer is a resin or polymer that acts as a medium for ion exchange, that is also known as an ionex. It is an insoluble matrix (or support structure) normally in the form of small (0.25–1.43 mm radiu ...

as the absorber in 1967. The authors proposed to regenerate the sorbent by washing it in a solution of

alkali In chemistry, an alkali (; from the Arabic word , ) is a basic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a soluble base has a pH greater than 7.0. The a ...

or soda. The study also showed that cartridges can be effectively regenerated after exposure to methyl bromide (when they are blown with hot air 100 to 110 °C, flow rate 20 L/min, duration about 60 minutes). Regeneration of sorbents is used consistently and systematically in the

chemical industry The chemical industry comprises the companies and other organizations that develop and produce industrial, specialty and other chemicals. Central to the modern world economy, the chemical industry converts raw materials ( oil, natural gas, air, ...

, as it allows cost savings on the replacement of sorbent and regeneration of industrial gas cleaning devices to be carried out thoroughly and in an organized manner. However, in the mass use of gas masks under different conditions it is impossible to control the accuracy and correctness such regeneration of respirators' cartridges. Therefore, despite the technical feasibility and commercial benefits, regeneration of respirator cartridges in such cases is not carried out.

References

External links

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OSHA math model tool for replacement of chemical cartridges
{{Breathing apparatus, industrial, state=expanded Safety equipment Respirators