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Indoor Air Quality and Ventilation in Photographic Processing Facilities • J-314(ENG) 7
levels but is not considered local
exhaust ventilation. A local exhaust
system may be more expensive to
install than a general dilution
ventilation system, but requires less
air (and energy) to effectively
control the airborne contaminants.
When designing local exhaust
systems, the objective is to capture
contaminants close to the source and
draw the contaminated air stream
away from the air you breathe.
Avoid placing workstations
between the source (photographic
processor) and the inlet to the
exhaust hood.
You can find information on the
proper design of local exhaust
systems in the ACGIH Industrial
Ventilation Manual (ACGIH 2001).
The design must also consider the
required “make-up” air system
you’ll need to replace and condition
the air that is exhausted from the
building. In addition, it is also
important to review local laws and
ordinances regarding local exhaust
and any permit requirements with
local, state, or federal regulators.
General dilution ventilation
following the minimum fresh air
recommendations from ASHRAE
(0.5 cfm/ft
2
of floor area) should be
effective at controlling air
contaminants associated with
minilab processes. In some cases,
venting the dryer section of the
processor to outdoors may be
appropriate to prevent excessive
humidity (greater than 60% relative
humidity) and odors in the
workplace. Consult with the
processor manufacturer for specific
venting requirements.
RECOMMENDATIONS
MINILABS
Dilution or general ventilation is
simply bringing in and distributing
enough fresh, uncontaminated air
(preferably outdoor air) to dilute the
indoor air contaminants to an
acceptable level.
Minimum recommendations for
general ventilation for buildings and
processes are provided by the
American Society of Heating,
Refrigeration and Air Conditioning
Engineers (ASHRAE).
For photographic processing
operations, ASHRAE Standard 62-
1989 recommends:
• 0.5 cubic feet per minute (cfm) of
fresh outside air, per square foot
(ft
2
) of floor area (0.5 cfm/ft
2
),
assuming a maximum occupancy
of 10 persons/1000 ft
2
in
darkrooms.
For example, if the room where
photoprocessing takes place is 10 ft
x 20 ft x 8 ft, the floor area is 200 ft
2
and the room volume is 1600 ft
3
.
Based on 0.5 cmf/ft
2
, you would
need to supply at least 200 x 0.5 or
100 cfm of fresh outside air to the
space.
The number of “room air changes
per hour” is determined by the fresh
air supply rate. In the example, in
one hour 6000 ft
3
(100 ft
3
/min x 60
min) of fresh air entered the space
(room volume: 1600 ft
3
). To calculate
the room air changes per hour, you
divide the total amount of fresh air
that has entered the space by the
volume of the room:
6000 ft
3
/hr/1600 ft
3
room volume =
3.75 air changes per hour.
It is important to note that the
ASHRAE recommendations
represent the minimum amount of
fresh air that should be supplied to
the space. Past recommendations
from Kodak have been as high as ten
air changes per hour.
DILUTION VENTILATION
When using dilution ventilation,
airborne contaminants are not
captured at the source. Instead, the
contaminated air is turned over and
replaced quickly enough to
minimize potential exposure and
related odors. To be most effective,
make sure you properly position the
supply air inlets and return air
outlets for good mixing/dilution of
the room air. Their placement must
minimize the potential for “short-
circuiting” or direct flow of supply
air to return with minimum room air
mixing (Figure 2). For a large room,
you may need supply air inlets and
return air outlets throughout the
room. Do not position the inlet and
outlets too close together.
Figure 2
Open tank processor with general room
dilution ventilation
Local exhaust ventilation is used to
capture air contaminants close to the
source of generation, before they can
enter the general work room air.
This type of ventilation can be very
effective at controlling airborne
contaminants. A general room
exhaust system will reduce airborne
LOCAL EXHAUST
VENTILATION
Supply Fresh Air