respirator - Modern respirator technology

A mechanical method of delivering oxygen to and removing carbon dioxide from patients who are unable to breathe for themselves. It expands the lungs intermittently through a tube introduced into the trachea. Simple portable apparatus is available that can be operated by hand when short-term ventilation is required. For more prolonged use, a number of automated machines are available. The original respirator was referred to as an ‘iron lung’; this was a large box enclosing the patient's body, excluding the head and neck. Entry of air into the lungs was achieved by intermittently lowering the air pressure within the chamber, thus expanding the patient's lungs and chest. This type of respirator was classically used with patients suffering from respiratory paralysis due to poliomyelitis, but it is no longer used.

For the mechanical device used to assist breathing, see ventilator.

A respirator is a device designed to protect the wearer from inhaling harmful dusts, fumes, vapors, and/or gases.

There are two main categories: the air-purifying respirator, which forces contaminated air through a filtering element, and the air-supplied respirator, in which an alternate supply of fresh air is delivered. 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 were provided for exhalation of used air.

The first US patent for an air purifying respirator was granted to Lewis P. Haslett in 1848 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.

Inventors were also developing air purifying devices across the Atlantic. He put his science to work in building 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. British physicist John Tyndall took Stenhouse's mask, added a filter of cotton wool saturated with lime, glycerin, and charcoal, and invented a 'fireman's respirator,' a hood that filtered smoke and gas from air, in 1871; 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.' German Bernhard Loeb patented several inventions to 'purify foul or vitiated air,' and counted among his customers the Brooklyn Fire Department. When the Canadians spotted the retreating Algerians, with their ashen purple faces, gasps for air, and an overbearing stench of chlorine, they knew something extraordinary and horrifying had occurred. when dry they did nothing to stop or filter chlorine, and when wet nothing could pass through them, not even air, making it impossible to use.

Modern respirator technology

All respirators have some type of facepiece held to the wearer's head with straps, a cloth harness, or some other method.

Air-purifying respirators

Air-purifying respirators are used against particulates (such as smoke or fumes), gases, and vapors. This class includes:

negative-pressure respirators, using mechanical filters and chemical media positive-pressure units such as powered air-purifying respirators (PAPRs)

Half- or full-facepiece designs of this type are marketed in many varieties depending on the hazard of concern. They use a filter which acts passively on air inhaled by the wearer. The latter are typically simple, light, single-piece, half-face masks and employ the first three mechanical mechanisms in the list below to remove particulates from the air stream.

Mechanical filter respirators

Mechanical filter respirators retain particulate matter when contaminated air is passed through the filter material.

Mechanical filters remove contaminants from air in the following ways:

by particles which are following a line of flow in the airstream coming within one radius of a fiber and adhering to it, called interception; this increases with diminishing fiber separation and higher air flow velocity by an enhancing mechanism called diffusion, which is a result of the collision with gas molecules by the smallest particles, especially those below 100 nm in diameter, which are thereby impeded and delayed in their path through the filter; it becomes dominant at lower air flow velocities 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 surface of the filter material; and 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.

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 passing through the filter medium as low as possible.

The greatest advance in mechanical filter technology has been the HEPA filter, invented during the Manhattan Project and now available to everyone. Most are NIOSH-approved:

Oil resistance	Rating	Description
Not 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
Somewhat 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
Strongly Resistant	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
*No NIOSH approvals are held by this type of disposable particulate respirator.

Chemical cartridge respirators

Chemical cartridge respirators use a cartridge to remove gases and vapors from breathing air by adsorption, absorption, or chemisorption.

Powered air-purifying respirators

Air-supplied respirators

Air-supplied units rely on a primary air source to deliver a consistent flow of breathable air – not oxygen, but regular air – to the user's facepiece.

Air line respirators

Self-contained breathing apparatus