Face Mask

Respirators come in a wide range of types and sizes used by the military, private industry, and the public. Respirators range from cheaper, single-use, disposable masks to reusable models with replaceable cartridges.
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.

Alexander von Humboldt introduced a primitive respirator in 1799 when he was working in Prussia as a mining engineer.
Practically all the early respirators 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 were provided for exhalation of used air.


Woodcut of Stenhouse's mask

The first US patent for an air purifying respirator was granted to Lewis P. 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.Hutson Hurd patented a cup-shaped mask in 1879 that became widespread in industrial use, and Hurd's H.S. John Stenhouse, a Scottish chemist, was investigating the power of charcoal, in its various forms, to capture and hold large volumes of gas.

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; Tyndall exhibited this respirator at a meeting of the Royal Society in London in 1874.

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.
Chemical warfare
The Second Battle of Ypres was the first time Germany used chemical weapons on a large scale on the Western Front in World War I and the first time a colonial force (Canadians) pushed back a major European power (Germans) on European soil, which occurred in the battle of St. The gas affects the lungs and the eyes causing respiration problems and blindness.Being denser than air it flowed downwards forcing the troops to climb out of trenches.
Eventually reserve Canadian troops held the front, being away from the attack, using urine-soaked cloths as primitive respirators. A Canadian soldier had discovered that the ammonia in urine would react with the chlorine, neutralizing it, and that the water would dissolve the chlorine, allowing the soldiers to breathe through the gas.

This is the first recorded response and defense against chemical attacks using respirators.
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. Facepieces come in many different styles and sizes, to accommodate all types of face shapes, and there are many books and references available for determining which kind of hazard requires what type of respirator.
Air-purifying respirators


Protective filter mask worn by NYPD officer

Air-purifying respirators are used against particulates (such as smoke or fumes), gases, and vapors that are at atmospheric concentrations less than immediately dangerous to life and health.

They use a filter which acts passively on air inhaled by the wearer. Some 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 mechanisms in the list below to remove particulates from the air stream. The entire unit is discarded after some extended period or a single use, depending on the contaminant.

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.
Mechanical filter respirators
Mechanical filter respirators retain particulate matter when contaminated air is passed through the filter material. Single-use, disposable as well as replaceable cartridge models are common.


Filtering half mask with exhalation valve (class: FFP3)

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;
by larger particles unable to follow the curving contours of the airstream being forced to embed in one of the fibers directly, called impaction; 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; this effect is similar to Brownian motion and raises the probability that particles will be stopped by either of the two mechanisms above; 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;
by using gravity and allowing particles to settle into the filter material (this effect is typically negligible); 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.

In between, near the 0.3 μm most penetrating particle size (MPPS), diffusion and interception predominate.
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. A HEPA filter can remove as much as 99.97% of all airborne particulates with aerodynamic diameter of 0.3 micrometres or greater.
United States NIOSH standards define the following categories of particulate filters:
European standard EN 143 defines the following classes of particle filters that can be attached to a face mask:
European standard EN 149 defines the following classes of “filtering half masks” (also called “filtering face pieces”), that is respirators that are entirely or substantially constructed of filtering material:
Both European standards test filter penetration with both dry sodium chloride and paraffin oil aerosols, after storing the filters at 70 °C and −30 °C for 24 h each.The standards also include tests on mechanical strength, breathing resistance and clogging. 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. The units consist of a powered fan which forces incoming air through one or more filters for delivery to the user for breathing.

They are not suitable when working with volatile organic compounds such as those used in many spray paints. An open-circuit SCBA has a full-face mask, regulator, air cylinder, cylinder pressure gauge, and a harness with adjustable shoulder straps and belt which lets it be worn on the back.