Pulmonary Protection

Respirators are devices that fit on the face or head to provide protection against hazards from dusts, mists, fumes, and vapors. Respirators are designed for specific hazards. Testing any respirator to obtain a good fit of the mask to the individual user's face (fit testing) is important. The vendor or respirator manufacturer can provide instructions on how this should be done. Many companies have a trained individual to do fit testing using special equipment or procedures, but for many agricultural operations it is up to each worker to follow the instructions and ensure the mask fits properly. Beards interfere with sealing and are generally not compatible with respirators.

Particulate Respirators

To prevent respiratory exposure to dusts, mists, and vapors, respirators are available in a variety of models. Particulate respirators, also known as dust and mist respirators, are intended for dusts from hay, silage, molds, soil particles, and the environment inside livestock buildings, which can consist of manure particles, feed particles, and animal dander. Mists are composed of relatively large suspended liquid particles and thus can be filtered by particu-late respirators, as opposed to vapors that must be filtered by other means. Particulate respirators should never be used when hazardous vapors will be present.

A particulate respirator is not the same as the simple dust mask often found at hardware or discount stores. An approved particulate respirator has been tested and approved by the National Institute for Occupational Safety and Health (NIOSH) or the Mine Safety and Health Administration (MSHA) and has an approval number, starting with the letters "TC." It can filter out small toxic particles like mold spores and is very useful in agricultural applications. It typically has two straps appearing relatively thick compared to those on a dust mask and covering the nose, mouth, and chin (3).

Dust masks are for nuisance dusts like sawdust or pollen, are relatively thin, and typically have one strap. They have not been tested and do not carry a TC approval number. Dust masks costs much less than true particulate respirators, perhaps one tenth as much, but they are not recommended. An unapproved dust mask should never be called a "respirator."

Particulate respirators are rated for protection against oil-based chemicals and overall filtering efficiency. To follow these ratings, manufacturers' recommendations should always be followed regarding proper duration and conditions of use (Table 6.2).

Particulate respirators may have special features. Some have exhaust valves that make breathing easier and also enable a better seal to be maintained with the face. Without an exhaust valve, exhalation tends to push the respirator away from the face. Some contain a layer of activated carbon to

Table 6.2. Rating system for particulate respirators.

Overall efficiency

at filtering particles

Rating letter

Rated as

95%

N

Not resistant to oils

99%

R

Resistant to oils (<8 hours)

100%

P

Oil proof

remove nuisance odors, not to be mistaken for true chemical respirators. Still others are designed specifically to protect against welding fumes (a fume is an aerosol of small particles from condensation of molten metals, such as from welding).

Some chemical respirators can be fitted with particulate filters, either for particulates alone or in series with a vapor cartridge as a pre-filter ahead of the particulate cartridge. These particulate filters are approved respirators and as such carry NIOSH approval numbers.

Chemical Respirators

Chemical respirators filter out vapors that are the gaseous form of a liquid or solid, such as gasoline. They also carry TC approval numbers. These respirators typically have cartridges of activated carbon and are color-coded for easy identification. Standard cartridges are black for organic vapors (pesticides and paints), green (ammonia), yellow (acid gases), and white (chlorine). Although color coding of cartridges is standardized, the shape and fit of cartridges among different manufacturers are not requiring use of cartridges specific to a given brand of respirator (1).

The cartridge instructions, along with chemical labels or MSDS for specific chemicals, should always be consulted to determine the correct cartridge. As mentioned earlier, particulate pre-filters can be used ahead of the chemical cartridge to prevent particulates from clogging the cartridges.

Cartridges are used on several types of chemical respirators. These include the half-mask with a replaceable cartridge, the disposable half-mask with fixed cartridges, and the full-face respirator. The half-mask respirator covers the nose, mouth, and chin, and seals against the top of the nose, cheeks, and chin. It is held in place by a pair of straps. Most have replaceable cartridges, allowing replacement when a cartridge's filtering ability is depleted and also allowing use of different cartridges in different applications. Some have fixed cartridges and must be discarded when the filtering ability is depleted.

The full-face respirator has a large clear face shield and seals around the entire face, so it protects the eyes as well as the respiratory system. Beneath the face shield is an inner seal that seals around the nose, cheeks, and chin like a half-mask respirator. Full-face respirators have replaceable canisters. A full-face respirator with a very large canister for increased duration of protection is sometimes referred to as a "gas mask."

Some tractor cabs are specifically constructed to provide respiratory protection against chemicals during pesticide spraying. Operators in these cabs may not be required to wear respiratory PPE. Replacement filters are available for some "ordinary" tractor cabs. These filters contain activated charcoal to filter vapors, but they are not approved as replacements for PPE and do not offer the protection of cabs designed and constructed for that purpose (1).

Powered Air-Purifying and Supplied-Air Respirators

Powered air-purifying respirators (PAPRs) are a helmet or hood with a fan that pumps filtered air into it. The filter generally consists of one or two cartridges for protection against chemicals and/or particulates, typically connected to the helmet by a flexible hose. Approved particulate filters for PAPR units carry a high-efficiency particulate air (HEPA) rating. Because a PAPR only filters air, it must not be used where inadequate oxygen concentrations are present (1).

For protection against atmospheres that are immediately dangerous to life or health (IDLH) due to lack of oxygen or the presence of toxic chemicals that cannot be adequately filtered, a supplied-air respirator is required. These respirators provide breathing air from portable tanks carried by the wearer, or by an air hose extending to a fixed air supply. Respirators with tanks are known as self-contained breathing apparatus (SCBA) and are commonly used by firefighters. They require special training and maintenance, and should only be used by trained personnel. Underwater SCBA for divers, known as self-contained underwater breathing apparatus (SCUBA), is not the same and should not be used as a substitute.

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