Breathing apparatus for personnel safety and protection

Atmospheres can be contaminated by dust or gas, or be deficient in oxygen. These hazards can occur singly or in any combination. In this chapter, the term dust includes mist and fume, and gas includes vapor. Each contaminant can have special characteristics of its own that require protection. Contaminated atmospheres are generally described as nuisance atmospheres that are not toxic or immediately dangerous to health, hazardous atmospheres that are of low toxicity or cause easily reversible biological changes, dangerous atmospheres of a high toxicity or where the health hazards are more severe, and atmospheres immediately dangerous to life. This chapter is designed to assist in the selection of respiratory protective devices for use against atmospheric contaminants.

Keywords

Respiratory protective; hazardous atmospheres; dust; self-contained breathing apparatus; air-purifying respirators; toxicity

1.1 Introduction

This chapter is designed to assist in the selection of respiratory protective devices (RPDs) for use against atmospheric contaminants. Atmospheres can be contaminated by dust, gas, or by being deficient in oxygen. These hazards occur singly or in any combination. In this context, dust can include mist and fume and gas can include vapor.

Each contaminant can have special characteristics of its own that require protection in addition to those discussed in this section. For instance, radioactive or corrosive materials require the use of special clothing. Some gases, liquids, and soluble solids absorb through the skin, and these also require special protection.

Contaminated atmospheres are generally described as nuisance atmospheres that are not toxic or immediately dangerous to health, hazardous atmospheres that are of low toxicity or easily cause reversible biological changes, dangerous atmospheres of a high toxicity or where the health hazards are more serious, and atmospheres immediately dangerous to life.

RPDs should either filter the contaminated atmosphere to produce air suitable for respiration, or supply such air from an alternative source. The air is supplied to the breathing area (the nose and mouth of the user) by one of the following: a mouthpiece and nose clip; a half-mask covering the nose and mouth; a full facepiece covering the eyes, nose, and mouth; a hood covering the head down to the shoulders; or a suit covering the head and body down to the waist and wrists.

In this chapter, for each type of RPD a nominal protection factor is given. This factor is a guide to the effectiveness of the device when used correctly. It indicates the degree to which the atmospheric contaminant is reduced by the respirator within the breathing zone. Thus, a device that reduces the level of contamination 10 times will have a nominal protection factor of 10, while one that reduces it 1000 times will have a nominal protection factor of 1000. These figures should be used in conjunction with the maximum allowable concentration, or threshold limit value, of the contaminant and its actual concentration in the atmosphere. Generally, a substance with a threshold limit value of 10 parts per million, which has a concentration of 1000 parts per million in the atmosphere, will require the use of equipment with a nominal protection factor of at least 100.

Breathing apparatus sets allow firefighters to enter areas filled with smoke or other poisonous gases. These sets consist of a cylinder that contains compressed air, a mask that is worn over the whole face, a gauge to tell the firefighter the pressure in the cylinder, a distress signal unit that activates if the firefighter stops moving, and other safety equipment. The cylinder can supply up to 45 minutes of air, although hard work and other factors can reduce this duration. Breathing apparatus (BA) is also available in a twin-cylinder configuration for longer use.

The following requirements will be discussed in more detail in subsequent sections of this chapter.

In the control of occupational diseases caused by breathing air contaminated with harmful dusts, fogs, fumes, mists, gases, smokes, sprays, or vapors, the primary objective is to prevent atmospheric contamination. This is accomplished as far as feasible by accepted engineering control measures (e.g., enclosure or confinement of the operation, general and local ventilation, and substitution with less toxic materials).

Respirators should be provided by employers when such equipment is necessary to protect the health of employees. Employers should provide respirators that are applicable and suitable for the task, and should establish and maintain a respiratory protective program that covers these general requirements.

Employee should use the provided respiratory protection in accordance with the instructions and training received, and should guard against damage to the respirator. Employees should report any malfunction of the respirator.

1.1.1 Minimal acceptable program

Standard operating instructions governing the selection and use of respirators should be observed. Respirators should be selected on the basis of the hazards to which workers are exposed. The user should be instructed and trained in the proper use of respirators and their limitations.

All types of BA should be regularly cleaned and disinfected. Those issued for the exclusive use of one employee should be cleaned after each day’s use, or more often if necessary. Those used by more than one employee should be thoroughly cleaned and disinfected after each use. Appropriate surveillance of work-area conditions and degree of employee exposure or stress should also be maintained. There should be regular checkups and evaluations to determine the continued effectiveness of the program.

The company’s industrial hygiene, health physics, safety engineering, or fire department should administer the program in close liaison with the company’s medical department. Responsibility for the program should be given to one individual to assure it is maintained. In small plants having no formal industrial hygiene, health physics, safety, fire, or medical department, the respirator program should be handled by an upper-level superintendent, foreman, or other qualified individual. The program’s administrator should also have sufficient knowledge to properly supervise the program.

1.1.2 Medical limitations

A firefighter should be assigned tasks requiring use of RPDs only if it has been determined that he is able to perform these tasks while using the device(s). Firefighters with punctured eardrums should wear earplugs. The assigned physician should determine what health, physical, and psychological conditions are pertinent. The firefighter’s medical status pertaining to use of RPDs should be reviewed at least annually.

1.1.3 Communication

Although full facepieces distort the human voice to some extent, the exhalation valve usually provides a pathway for speech transmission over short distances. Also, most types of full facepieces are available with speaking diaphragms to improve speech intelligibility. In addition, there are a variety of electronic communication units that utilize a microphone inside the full facepiece, connected directly to an amplifier and speaker, to a telephone, or to a radio transmitter. Connecting cables from microphones pass through the face piece. If the cables are removed for any reason, they should be carefully replaced or any hole in the facepiece should be carefully sealed.

1.1.4 Use of unapproved respiratory protective devices

Unapproved self-contained breathing devices are risky and should not be purchased or used.

Some of the problems associated with the use of full facepieces at low temperatures are poor visibility and freezing of exhalation valves. All full facepieces should be designed so that incoming fresh-air sweeps over the inside of the eyepieces to reduce misting. Anti-mist compounds should be used to coat the inside of eyepieces to reduce misting at room temperatures and down to temperatures approaching 0°C. Full facepieces are also available with inner masks that direct moist exhaled air through the exhalation valves, and when properly fitted are likely to provide adequate visibility at low temperatures.

At very low temperatures the exhalation valve collects moisture and may freeze open, allowing the user to breathe contaminated air, or freeze closed, preventing normal exhalation. Dry air suitable for respiration should be used with self-contained and compressed airline BA at low temperatures. The dew point of the breathed gas should be appropriate to the ambient temperature. High-pressure connections on self-contained BA will leak because of metal contraction at low temperatures, but the only problem is likely to be an outward leak.

A worker in areas of high ambient or radiant temperatures is under stress, and any additional stress caused by the use of respiratory protective devices should be minimized. This can be done by using devices having low weight and low breathing resistance. Supplied air respirators, hoods, and suits with an adequate supply of cool breathing air should be used.

1.2 Selection of respiratory protective equipment

A respiratory protective device (RPD), also known as a respirator, is a piece of safety equipment used for personal protection. Respirators are designed to prevent the inhalation of contaminated air and belong in two main categories: