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The air may be supplied from a compressor or from compressed air cylinders that are outside the contaminated area. In using compressors, the air intake needs to be properly located to prevent the contaminant becoming entrained in the air supply. In-line filters and traps to remove oil, dust, condensate and odour from compressed gases should be provided as necessary to yield breathable air of an acceptable quality. Large compressors or cylinders are necessary, which may affect measures for atmospheric control in some locations such as vented rooms at subatmospheric pressure.
A face mask is connected through a belt mounted flow control valve to the compressed air line. To save air, especially when using compressed air cylinders, the flow control valve may be replaced by a lung demand valve, preferably of the positive pressure type, which provides a higher protection factor. It can reduce the air flow requirements by a factor of three, which also improves the quality of voice communication. High airflows cause noise and wearer discomfort (cooling or dehydration). With an adequate airflow, an effective positive pressure can be maintained in the mask to provide a high NPF. Some masks are also provided with a filter (F) for emergency escapes and to allow the worker movement through air locks.
A hood or blouse is connected to the compressed air line attached to a belt and may incorporate a valve by which the wearer can increase the flow rate of air supplied above the necessary minimum. The wearer’s comfort is relatively high in combination with moderately high protection. An auxiliary respiratory protection system, for example a filter, may also need to be worn if the wearer has to disconnect the air line to pass through air locks.
Full face mask with compressed air line and auxiliary filter.
A suitable compressor may supply several workers. Air supply may affect atmospheric control measures. Some equipment allows a degree of control over the air supply by the user.
27. SELF-CONTAINED BREATHING APPARATUSA self-contained breathing apparatus (SCBA) consists of a full face mask supplied with air or oxygen from compressed gas cylinders carried by the worker. Air is supplied to the mask through a positive pressure demand valve.
Alternatively, oxygen is supplied at a constant low flow rate (4 litres per minute) to replace the oxygen consumed. This is achieved in a closed system that collects the exhaled gases, routes them through a soda lime cartridge to remove the carbon dioxide, and then adds oxygen to make up the fresh gas.
Both types can be obtained with positive pressure regulators.
An SCBA provides mobility but is bulky and heavy. Compressed air apparatus protects for up to 45 minutes and oxygen apparatus for up to four hours.
Extensive training is necessary for the wearers and for those who maintain the equipment. An SCBA is difficult to decontaminate and should be worn under a protective suit when used in contaminated areas.
A type of SCBA that generates oxygen chemically can be used in emergency situations for up to one hour. It is less bulky than compressed oxygen cylinders and has a long shelf life. Oxygen is generated from sodium chlorate or potassium superoxide. The latter is more expensive but has the advantage of releasing oxygen in amounts equal to the exhaled carbon dioxide absorbed.
Self contained breathing apparatus (SCBA) with a demand valve.
Open SCBA systems supply from a cylinder and vent to the atmosphere. Closed systems process the exhaled gases and replace the used oxygen. SCBAs provide mobility and high APF/NPF but are bulky and heavy. Extensive training is necessary.
SCBAs should be protected against radioactive contamination.
28. COMPRESSED AIR LINE WITH FULL SUIT
A ventilated pressurized suit enclosing the whole body (arms and legs) may be in one or two parts. Halved suits are sealed together at the waist. Full suits may have a gas tight zipper. The hood has at least the front section transparent, offering minimum distortion or interruption to the wearer’s vision. The compressed air supply hose is attached to a belt to withstand the stresses of being dragged. A valve may be attached to the belt to allow the wearer to control the air supply, either to the whole suit or to the hood, according to the design. Exhaust gases are discharged through exhaust valves in the suit body. Part of the air supply may cool the suit.
Full suits offer among the highest NPFs of all PPE. Higher air flow rates provide cooling if necessary and, if no face mask is incorporated, exhaled carbon dioxide needs to be flushed out to maintain its concentration in inhaled air below acceptable levels (less than 1 Vol% carbon dioxide). High overpressures of the suit cannot be achieved. Some substances can permeate or diffuse through the material, making the NPF dependent on the properties of the material and the flushing rate of the suit. An additional respirator should be worn under the suit if it is likely that a suit may become damaged.
There are usually sufficient reserves of air in a suit to allow the worker to egress through air locks after disconnection of the air supply, but for lengthy decontamination procedures breathing equipment may be necessary. Some suits are provided with an emergency breathing device to be used for escape purposes in the event of failure of the primary air supply.
In addition to radiological risks, there may be other hazards in the area(s) in which PPE is used. PPE can also create other problems and exacerbate hazards. For example, a worker’s field of vision may be reduced while wearing respiratory protection, vocal communication may be severely restricted or a hood may impair hearing. Such conditions increase the worker’s vulnerability to normal hazards and necessitate increased awareness and care.
Several types of PPE may be necessary to work safely. To protect against physical injury, head, eye and toe protection may be necessary. A safety helmet (‘bump cap’) may be worn when wearing enclosed suits or hoods.
Safety goggles may be worn inside ventilated suits. It is an advantage if the one PPE used incorporates all necessary protection, such as the ventilated helmet (see Section 23); if a respirator has eyepieces made from polycarbonate; or if integral boots have protective toecaps. Use of an eye shield with a respirator will severely limit the already restricted vision. Welding in a radioactive environment necessitates specially modified PPE, with the hoods of ventilated garments fitted with a welder’s mask, eye protection and an outer protective apron to protect against hot debris.
Suits made from aluminized fire resistant materials are available to protect against extreme radiant heat and, in hot environments, a cooled suit (see Section 28) should be used. Suits resistant to attack by specific chemicals should be assessed before use in respect of their contamination control.
Full suit with additional eye, ear, head, hand and foot protection.
Personal protective equipment can increase the wearer’s vulnerability to other hazards. PPE may be designed to protect against several hazards.
The designated areas in which PPE needs to be worn must be identified, clearly demarcated and described in written procedures with details of the PPE to be used.
As a reminder to workers who are familiar with the conditions for the use of PPE, and as a warning to visitors, suitable notices in the local language to deny unauthorized access should be posted at the barriers around the designated areas. It is preferable for the notices to display signs and symbols, which do not depend on the observer’s literacy. A system of signs using distinctive and meaningful shapes, colours and idealized symbols has been developed. A trefoil symbol on a yellow background within a black triangle indicates the potential presence of ionizing radiation. It could be accompanied by the words ‘Radioactive Contamination’. A sign with a person in silhouette on a white background within a red circle and a diagonal red bar prohibits unauthorized entry. Other signs with a blue background may display a symbol indicating the type of PPE that has to be worn by those about to enter the area. A head wearing a full face mask respirator indicates that RPE has to be worn by those about to enter the area and a symbol depicting boots indicates that the footwear used has to have protective toecaps.
Signs and symbols.
Appropriate signs are placed at the barrier on the edge of the designated area. The shape and colour of the signs and symbols may be coded to indicate ‘danger’, ‘must do’ and ‘do not’. The triangle containing a trefoil symbol warns that there is a potential hazard of ionizing radiations present. A circle with a symbol of a person in silhouette and a diagonal bar prohibits entry. Circular signs containing symbols depicting a head or mask, boots or ear defenders, for example, demand the use of PPE in the areas in which the signs are displayed.
European Standard EN 340: 1993, Protective Clothing — General Requirements.
European Standard EN 1073-1: 1998, Protective clothing against radioactive contamination — Part 1: Requirements and test methods for ventilated protective clothing against particulate radioactive contamination.
European Standard EN 1073-2: 2002, Protective clothing against radioactive contamination — Part 2: Requirements and test methods for non-ventilated protective clothing against particulate radioactive contamination.
INTERNATIONAL ORGANIZATION FOR STANDARDIZATION,Radiation Protection, Clothing for Protection against Contamination, Design, Selection, Testing and Use, ISO 8194, ISO, Geneva (1987).
INTERNATIONAL ATOMIC ENERGY AGENCY, INTERNATIONALLABOUR OFFICE, Occupational Radiation Protection, Safety Standards Series No. RS-G-1.1, IAEA, Vienna (1999).
INTERNATIONAL ATOMIC ENERGY AGENCY, INTERNATIONALLABOUR OFFICE, Assessment of Occupational Exposure Due to Intakes of Radionuclides, Safety Standards Series No. RS-G-1.2, IAEA, Vienna (1999).
INTERNATIONAL ATOMIC ENERGY AGENCY, Workplace Monitoring for Radiation and Contamination, Practical Radiation Technical Manual, IAEA-PRTM-1 (Rev. 1), IAEA, Vienna (2004).
INTERNATIONAL ATOMIC ENERGY AGENCY, Personal Monitoring, Practical Radiation Technical Manual, IAEA-PRTM-2 (Rev. 1), IAEA, Vienna (2004).
INTERNATIONAL ATOMIC ENERGY AGENCY, Health Effects and Medical Surveillance, Practical Radiation Technical Manual, IAEA-PRTM-3 (Rev. 1), IAEA, Vienna (2004).
A qualified expert, a librarian or the IAEA can recommend further reading on the topic of personal protective equipment.