patients per week and must be determined from the medical center prior
to the system design.
(d) Exhaust fan shall be on emergency power.
(e) Exhaust registers shall be located at floor and ceiling level.
4.12.3 VENTILATION CALCULATIONS
For restricted areas (Imaging Room and Hot Laboratory) the supply air
quantities, calculated on the basis of the room heat gains due to
occupancy, lights, equipment, and fenestration, should be matched with
the exhaust air quantities required to dilute the xenon gas
concentration.
4.12.3.1 Imaging Room
(a) Exhaust Air Quantity Calculations: The exhaust air quantity
discharged into the unrestricted area is calculated on the basis of the
following:
A x f = MPC x V x T x 60
A = Dose of Xenon Gas Used Per Week
= Number of Patients Per Week x Dose Per Patient
The average dose per patient, according to the DVA Nuclear Medicine
Department, St. Louis, MO, is 20,000 micro-curies. Micro-curie is a
unit of activity.
f=Fraction of the total dose lost to the patient examination room. It
is estimated that 20 percent of the total activity used per week is
lost. Use f = 0.2.
MPC = Maximum Permissible Concentration 3 x 10-7 micro-curies per
milliliter of the space volume for unrestricted area per NRC's
recommendation.
V = Exhaust Air Volume Milliliter Per Minute
T = Time in Hours Per Week. Unless stated otherwise, use 40 hours per
week.
60 = Minutes Per Hour
V = Air flow - CFM
V=
A x F CFM___________
MPC x T x 60 x 2.832 x 104
1 Cubic Feet = 2.832 x 104 Milliliters
(b) Spill Clearance Time: The above exhaust air volume should be used
as the basis to determine the amount of time, in minutes, required to
clear an accidental gas spill. While there is no maximum or minimum
time limit prescribed by the NRC, the DVA Nuclear Medicine Department
believes the spill should be cleared within 15 to 20 minutes. The spill
clearance time is calculated by the following equation:
HVAC DESIGN MANUAL
4-6
HVAC REQUIREMENTS FOR UNOCCUPIED AREAS
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