How To Make A Gas Mask Filter

Gas Mask

Background

A gas mask is a device designed to protect the wearer from noxious vapors, grit, and other pollutants. Masks may be designed to bear their own internal supply of fresh air, or they may be outfitted with a filter to screen out harmful contaminants. The latter type, known equally an Air Purifying Respirator (APR), consists of a tight-fitting face piece that contains one or more filter cartridges, an exhalation valve, and transparent middle pieces. The first Apr was patented in 1914 by Garret Morgan of Cleveland, Ohio, an African American inventor likewise credited with major improvements in the traffic signal. When the Cleveland Waterworks exploded in 1916, Morgan showed the value of his invention by entering the gas-filled tunnel under Lake Erie to rescue workers. Morgan'southward device afterwards evolved into the gas mask, used in Earth State of war I to protect soldiers confronting chemicals used in warfare.

Since that early time, there take been significant advances in gas mask engineering science, particularly in the area of new filtration aids. In addition, masks take been made more than comfortable and tighter fitting with modern plastics and silicone rubber compounds. Today APRs are used to filter many undesirable airborne substances, including toxic industrial fumes, vaporized paint, particulate pollution, and some gases used in chemical warfare. These masks are produced in several styles, some that encompass only the oral cavity and nose and others that cover the entire face, including the eyes. They may be designed for military machine equally well as industrial utilise only, even though the two types are similar in blueprint, the military masks must meet different standards than those used in industry. This article will focus on manufacture of the full face up type of mask used for industrial applications.

Raw Materials

A full-face up gas mask consists of a filter cartridge, flexible face covering piece, transparent eye lenses, and a series of straps and bands to hold the device snugly in place. The filter cartridge is a plastic canister 3-4 inches (eight-10 cm) beyond and 1 inch (two.5 cm) deep, which contains a filtration aid. Carbon based filtrants are normally used because they tin adsorb large quantities of organic gases, especially high molecular weight vapors like those used in chemical warfare. However, inorganic vapors are not usually strongly adsorbed on carbon. The adsorptive backdrop of carbon tin can exist enhanced by impregnating the particles with specific reactants or decomposition catalysts. Such chemically treated carbon is known as "activated carbon." The type of activated carbon employed in a given filter cartridge depends on the specific type of industrial contaminant to exist screened. For example, carbon treated with a combination of chromium and copper, known as "Whetlerite carbon," has been used since the 1940s to screen out hydrogen cyanide, cyanogen chloride, and formaldehyde. Today, due to concerns about chromium toxicity, a combination of molybdenum and triethylenediamine is used instead. Other types of activated carbon employ silverish or oxides of iron and zinc to trap contaminants. Sodium-, potassium- and alkali-treated carbon are used to absorb sewage vapors (hydrogen sulfide), chlorine, and other harmful gases.

Gas Mask

The "skirt," or face-covering piece, of the mask is used to agree the other components in identify and to provide a secure seal effectually the face area. Depending upon mask design, an exhalation valve may be inserted in the face up slice. This ane-fashion valve allows exhaust gases to exist expelled without assuasive outside air into the mask.

The eyepieces used in gas masks are chemically resistant, clear plastic lenses. Their primary function is to ensure the wearer's vision is not compromised. Depending on the industrial surroundings in which the mask is to be used, the eyepieces may take to be specially treated to be shatterproof, fog resistant, or to screen out sure types of calorie-free. Virtually gas mask manufacturers do not make their ain eyepieces; instead they are molded from polycarbonate plastic by an outside supplier and shipped to the manufacturers for associates.

The elastic straps that hold the mask on the face are typically fabricated of silicone rubber. Supplementary straps may be added to let the mask to be comfortably hung effectually the cervix during breaks in piece of work.

Design

The pattern of the mask itself varies by the industrial awarding. Some masks are designed with speech diaphragms, some are congenital to take extra filters, and others are made to be connected to an extenal air supply. Although the cardinal design does not vary for a given type of mask, the kind of filtrant used will vary depending on the product'south intended use. Manufacturers stock a variety of mask styles and cartridge filtrants. When they receive orders for a specific type of mask, they can custom design a mask that has the appropriate features.

The Manufacturing
Process

The canister is fabricated from styrene plastic, which is resistant to h2o and other

chemicals, has good dimensional stability, and is specially designed for injection molding. Injection molding is a process by which molten plastic is injected into a mold nether high pressure. The mold used for gas mask canisters consists of two disk-shaped pieces of metal that are clamped together. The plastic resin is liquefied by heating and and then injected into the mold via an injection plunger. The mold is then subjected to loftier pressure. Most injection machines compress the mold with a pressure ranging from 50-2,500 tons (51-2,540 metric tons). After the molten plastic has been compressed, cooling water is forced through channels in the mold to cool and harden the plastic. The pressure is released, the 2 halves of the mold are separated, and the finished canister is ejected.
Styrene is a thermoplastic resin, which means it can exist repeatedly remelted, then the scrap pieces can be reworked to make boosted canisters. Therefore, in that location is very little wasted plastic in this procedure. A like molding process is conducted to create small circular screens that fit inside the canister. The screens are designed to hold the activated carbon in place within the cartridge. Equally the canisters travel down the associates line, one screen is inserted, the canister is filled with the advisable filtrant, then the second screen is put into place.
The face slice is injection molded from silicone safe. Silicone rubber has outstanding stability, is resistant to loftier temperatures, and can conform to curves in the face and head. Information technology is also thermoplastic and tin remolded as necessary. The molding process is very similar to the one described to a higher place. Later on molding the skirt must be removed from the mold, and whatever rough edges must exist cleaned off by manus before the other components tin can be attached.
The pieces are assembled on a partially automated assembly line with two to four line workers supervising the process. The completed filter canister is attached to the confront slice and the eyepieces are inserted and held in place with adhesive. Finally the straps and bands are attached to the face piece with metallic rivets. When assembly is complete, the mask is given a last quality check. When the masks pass inspection, they are identified with the advisable markings in accord with the American National Standard for Identification of Air Purifying Respirator Cartridges and Canisters. The finished masks are packaged for shipping. The containers used to package the masks must also designate the identity of the mask. Furthermore, they must be designed for easy access if the masks might be used in the consequence of an emergency.

Byproducts/Waste product

Depending on the blazon of chemical handling the activated carbon has been exposed to, information technology may be classified equally chemic waste. This is the case with some filtrants, such equally chromium-treated carbon. The injection molding process used for the canisters and the face pieces generates little waste since any lost resin tin be remelted and used again. The lenses are manufactured by an outside vendor, so gas mask manufacturers exercise not take to address the issue of waste polycarbonate.

Quality Control

Gas masks, and air purifying respirators in full general, are regulated past the Code of Federal Regulations (CFR). These regulations specify the type of masks to use for a specific application. Examples of the different mask types recognized by the CFR include cocky-contained animate apparatus, not-powered air purifying particulate respirators, chemical cartridge respirators, and grit masks. The regulations stipulate the exact kind of testing that must exist done to ensure the quality of the finished product. The blazon of testing depends on the masks' final awarding, that is, what kind of contaminants it will be expected to filter. The CFR specifies the types of contaminants that the gas must be tested with, and it also stipulates the conditions nether which the testing must exist conducted. For case, some masks must be exposed to the contaminant for long periods of time. Others must be tested nether specific temperature and humidity atmospheric condition. This is washed by drawing an air stream contaminated with a known corporeality of poison through the mask. The amount of time required for the contaminant to saturate the filter and begin to laissez passer through is then measured.

Testing is washed at several points in the manufacturing procedure. There is an initial inspection of incoming goods to ensure they meet minimum quality specifications. This includes the filtrants, the resins used for molding, and the finished eyepieces as they are received. The canister must be tested after assembly to ensure it has proper seal and that the carbon filter works. The mask is tested once over again after all componentry has been assembled. The final mask may be placed on a mannequin head to ensure that the seal is tight and that the mask maintains its seal in movement.

The Future

Over the terminal 80 years, the basic technology of gas masks has been tested repeatedly, and and so is not likely to change in the future. The challenge for the APR industry volition be to develop products for special purposes, such as infant respirators or masks for persons with head wounds and other disabling injuries. The futurity of these products as well relies on advances in the material sciences, which allows production of smaller, more lightweight products. In fact, current enquiry efforts in carbon chemistry are predictable to effect in the development of a filter canister that is only half the size of the current standard and is more constructive. These and other improvements in materials volition result in new generations of respirator devices for industrial use, besides every bit for medical and military applications.

— Randy Schueller