Supply air should be appropriately filtered and conditioned in accordance
with operational requirements and with the levels recommended for
The ventilation rate in process areas where uncontained radioactive
materials are handled should be from 12 to 60 air changes per hour
(ORNL, 1970) depending on whether the area is normally occupied by
workers, the need for removal of process or decay heat, and the need for
removal of decay fumes. A minimum of eight air changes per hour
should be provided in support facilities within the process area. Adequate
air filters should be used at the intake of the ventilation supply system to
minimize dust in the process area and to reduce the dust loading on
A downward air-flow pattern should be provided at worker locations to
direct air from any potential leak point down and away from the worker's
face. Consideration should be given to the distribution of inlet air
through a number of small ports or by slot-type distributors to decrease
the possible occurrence of "dead spots" with little air circulation.
Glove boxes, conveyors, and other systems that require a controlled
atmosphere may be equipped with a recirculating air system. All parts of
the system should operate at air pressures that are negative with respect
to the room. Process enclosures that use normal air may receive their air
supply from the room through dust-stop and HEPA filters mounted on
the glove box.
Consideration should be given to isolating process rooms from each
other during accidents. The principle of compartmentation and separation
should be extended to systems handling ventilation in working areas by
the most practicable use of individual ventilation systems. Emergency
damper cutovers between adjacent individual ventilation systems.
Redundancy can be minimized by the provision of a back-up unit for
each two individual systems.
The number of required exhaust-filtration stages from any area of the
facility should be determined by analysis to limit quantities and
concentrations of airborne radioactive or toxic material released to the
environment during normal and accident conditions. Materials released
should be in conformance with applicable standards, policies, and
guidelines. In general, each exhaust filter system should consist of a
minimum of two HEPA filters for room air and three HEPA filters in
series for glove-box or hood-exhaust air. Only two stages of glove-box or
hood exhaust filters need to be equipped for in-place testing.