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Physiology of Respirator Use
Know the Human Response and Effect on Endurance

Wearing any respirator, alone or in conjunction with other types of protective equipment, will impose some physiological stress on the wearer. Weight of the equipment, for example, increases the energy requirement for a given task.

Selection of respiratory protective devices, according to the National Institute for Occupational Safety and Health should be based on breathing resistance, weight of the respirator, the type and amount of protection needed, as well as the individual’s tolerance of the given device.

Use of respirators in conjunction with protective clothing can greatly affect the human response and endurance, especially in hot environments. Normally, in hot environments or during heavy work, the body relies a great deal on heat loss through the evaporation of sweat. With impermeable clothing, the heat loss by water evaporation is not possible.

Additionally, the weight of the respirator (up to 35 pounds for a self-contained breathing apparatus) adds to the metabolic rate of workers, increasing the amount of heat the body produces. The net effect is one of heat stress.

NIOSH studies of workers wearing chemical protective clothing (CPC) and firefighters’ ensembles have indicated that heat stress is a serious consideration. Significant physiological stress was observed, even at low work intensities (30 percent of maximum work capacity – level walking at 3.4 miles per hour) in a neutral environment (23º C and 55 percent RH).

With the CPC ensemble, worker tolerance time was reduced by 56 percent as compared to light work clothing only. Elevated temperatures were observed in 33 percent of subjects.

With the heavier firefighters’ ensemble, tolerance time was reduced by 84 percent as compared to light work clothing only, and heart rates averaged 25-50 beats per minute higher than with lightweight work clothing. At higher work intensities (60 percent of maximum), tolerance time was decreased by as much as 96 percent.

Based upon this limited research, NIOSH has made the following recommendations:

1. Select the lightest weight protective ensembles and respiratory protective devices that adequately protect the worker. This will minimize the physiological demands placed on the worker by carrying the weight of this equipment.

2. If available, select protective clothing made of material that will allow evaporation of water vapor, while providing skin protection from the contaminant.

3. Reduce work rate by:

a. Adjusting the work/rest schedules;

b. Using automated procedures and/or mechanical assistance where possible, and;

c. Minimizing the work intensity.

4. Educate workers on the symptoms and prevention of heat illness and schedule periodic fluid replacement breaks.

5. Reduce heat stress by scheduling work at night or early morning or by providing external cooling, where possible (either through cooling garments and/or by providing cool respirable breathing air through pressure-demand air supplied respirators); and

6. When conducting pipe/boiler lagging removal, ensure that steam lines are cool to minimize heat exposure from these sources.

Low and High Temperatures

Low temperatures may fog respirator lenses. Coating the inner surface of the lens with the anti-fogging compound normally available from the respirator manufacturer should prevent fogging down to 32º F, but severe fogging may occur below 0º F. Full face pieces with nose cups that direct the warm, moist exhaled air through the exhalation valve without its touching the lens, are available.

They should provide satisfactory vision at as low as –30º F. At very low temperatures, exhalation valves may freeze due to moisture. Dry respirable air should be used with airline respirators and with the type of SCBA that has an air cylinder when they are used in low temperatures.

NIOSH performs cold temperature testing on SCBA, and the minimum temperature that the SCBA has been tested to and approved for should be listed on the approval label.

A person working in high temperature air is under stress. Wearing a respirator causes additional stress, which should be minimized by using a light-weight respirator with low breathing resistance. In atmospheres that are not immediately dangerous to life or health the airline type supplied-air respirator is recommended. Such a respirator used in low or high temperature atmospheres may be equipped with a vortex tube to either warm or cool the air supplied.

Dangerous Atmospheres

Written procedures should be prepared for safe respirator use in immediately dangerous to life or health (IDLH) atmospheres that may occur in normal operations or emergencies. Personnel should be familiar with these procedures and respirators.

At least one standby person, equipped with proper rescue equipment including an SCBA should be present in the nearest safe area for emergency rescue of those wearing respirators in an IDLH atmosphere.

Communications (visual, voice, signal line, telephone, radio, or other suitable type) should be maintained among all persons present (those in the IDLH atmosphere and the standby person or persons). The respirator wearers should be equipped with safety harnesses and safety lines to permit their removal from the IDLH atmosphere if they are overcome.

Confined spaces are enclosure that are difficult to get out of, such as storage tanks, tank cars, boilers, sewers, tunnels, pipelines, pits and tubs. The atmospheres in a confined space may be immediately dangerous to life or health because of toxic air contaminants or lack of oxygen. Before anyone enters a confined space, tests should be made to determine the presence and concentration of any flammable vapor or gas, or any toxic airborne particulate, vapor, or gas, and to determine the oxygen concentration.

The confined space should be force-ventilate to keep the concentration of a flammable substance at a safe level. No one should enter if a flammable substance exceeds the lower explosive limit. No one should enter without wearing the proper type of respirator if any air contaminant exceeds the established permissible exposure limit or if there is an oxygen deficiency.

Even if the contaminant concentration is below the established breathing time weighted average limit and there is enough oxygen, the safest procedure is to ventilate the entire space continuously if people are to work in the confined space without respirators.

Airline and hose mask type supplied-air respirators or appropriate air-purifying respirators may be worn in a confined space only if tests show that the atmosphere contains adequate oxygen, and that air contaminants are below levels immediately dangerous to life or health. While people wearing these types of respirators are in a confined space, its atmosphere should be monitored continuously.

If the atmosphere in a confined space is IDLH owing to a high concentration of air contaminant or oxygen deficiency, those who must enter the space should wear a pressure-demand SCBA or a combination pressure-demand airline and SCBA that always maintains positive air pressure inside the respiratory inlet covering. This is the best safety practice for confined spaces.

While personnel are in a confined space, at least one standby person with proper rescue equipment, including an SCBA, should be present outside for emergency rescue.

Communications (visual, voice, signal line, telephone, radio or other suitable type) should be equipped with safety harnesses and safety lines to allow their removal in case they are overcome. FSM

Source: NIOSH Guide to Industrial Respiratory Protection.