Document 71rgn08XpYOq79BODqd3KwJD8

PERSONAL PROTECTIVE EQUIPMENT Fig. 36-20. Single-cartridge chemical res pirator Twin-cartridge units are also available and give longer life and less breathing resistance gency situations, that is, for atmospheres which are harmful only after prolonged or repeated exposures At the present time. Bureau of Mines' approval has been given only for type B (organic vapor) and type BE (dusts, fumes, and mists in combination with organic va pors) These types are approved for con centrations not m excess of 1,000 parts of organic vapor per one million parts of air Mechanical filter respirators A mechanical filter respirator can be de signed to give satisfactory protection against any land of particle (Fig 38-21) The major items to he considered are the resistance to breathing offered by the fil tering element, the adaptation of the facepiece to faces of various sizes and shapes, and the fineness of the particles to be fil tered out The types of mechanical filter (disper sed) respirators approved by the Bureau o! Mines are as follows. Pnewnocontosis-producmg and nuisance dust respirators, which provide respiratory protection against pneumoconiosis-pro ducing dusts, such as aluminum, cel lulose, cement, charcoal, coal, coke, flour, gypsum, iron ore, limestone, and wood Tone dust respirators, which provide re spiratory protection against toxic dusts that are not significantly more tome than lead, such as arsenic, cadmium, chromium, lead, manganese, selenium, vanadium, and their compounds Mist respirators, which provide respiratory protection against pneumoconiosis-pro ducing, chromic acid, and nuisance mists Fume respirators, which provide respira tory protection against fumes (solid dispersoids or particulate matter formed by the condensation of vapors such as those horn heated metals and other sub stances) Dispersoid respirators have been ap proved that will give respiratory protection against two or more of the above types of contaminants. The Bureau of Mines requires that the complete respirator show a resistance to in halation not in excess of 50 mm (2 in ) of water pressure at an inhalation rate of 85 liters (3 cu ft) of air per minute Manv respirators approved by the Bureau of Mines have considerably lower resistance Low breathing resistance requires a fair ly large area of filtering medium Fineness of the filter is fixed by the permissible leak age for various dusts It is important that breathing resistance be low even after the respirator has had considerable use under dusty conditions Excessive breathing re sistance wastes energy and may be the source of lung injury if long continued Filters of high porosity may give low breathing resistance with small filter area, but they will not stop fine dust All such filters do is to improve comfort by catch ing the larger particles, which are usually caught m the nose and throat anyhow Breathing out against resistance does not engender the psychological effect that re sistance to inhalation does However, it can be detrimental m that it is physically tiring. Combination respirators Combination chemical and mechanical fil ter respirators utilize dust, mist, or fume filters with a chemical cartridge for dual or 9S-34