• Darkrooms

Darkroom applications naturally preclude light, therefore mechanical ventilation is essential in order to remove the heat generated from equipment, in particular, dryers, print glazers and other heat generating equipment.

Normally, an enclosed room would require ducted fans, which tend to be ducted through blacked out windows, roots and through walls to ensure exclusion of light ingress.

In general, darkrooms should be ventilated at a rate of not less than 10 air changes per hour. Where a print glazer, dryer or other heat producing equipment is in operation, 15 air changes per hour should be given. Small dark rooms for occasional use or for purely developing processes may often be ventilated naturally with a suitable light trap, although consideration should be given to providing mechanical extract using an air change rate of spa air changes per hour.

A typical darkroom is split into two sides, the one side with the sink, often referred to as the wet side is where all the chemical mixing, film processing and paper processing takes place. The dry side on the other hand is where all printing, cutting and finishing work is undertaken. Ventilation is very important and an active vent with a fan to exhaust all of the fumes to the outside of the darkroom is required. Furthermore, it is essential that the ventilation system is light tight.

By having the room light tight, this may also mean the door to the room might also be virtually airtight. In small dark rooms, it is advisable to take frequent breaks from the work to open the door and provide good ventilation. If the room is airtight then the fan will not be able to push air into the room without straining therefore the room needs an inlet, so that the fan can draw air into the room. A light tight air inlet is easily made on an inside wall of a darkroom. Air can be drawn from the rest of the house and pulled into the darkroom, and extracted via the tan to the outside of the room.

By installing an extract fan, there are considerations:

First of all, it depends where the darkroom is situated in the home. Where one of the walls of the darkroom is also an exterior, above ground wall of the house, the fan can be mounted above the processing area, venting horizontally through the wall ensuring this is light tight.

Where the room is more in the center of the house, or below ground, this is more restrictive. Here, the fan could be mounted in the ceiling between the joists and then vent along between the joints to the outside wall of the house. In this instance, a protective hood should be fitted to deflect any rain water and a screened opening will prevent rodents, etc. from entering the house.

The intake size will depend somewhat on the power of the fan, therefore the intake should be large enough to allow the fan to run without straining too much.

It is advisable to fit a fan with variable speed control, so the fan can be set to high speed for a few minutes to clear the obvious fumes, especially fixer, then turn the fan speed down to a more tolerable level, or even tum it off or open the door for a while when the air gets stale or stuffy.

For general purpose dark rooms, however, the air change rate should be ascertained from consideration of the heat gain from the enlarger, lights, as well as the occupants, on the basis of a temperature rise of 5-6°C. With industrial and commercial darkrooms that have machine processing, the machines will very often have their own extract ducting, the air supply being drawn from the room itself. It will usually be necessary to provide a warmed and filtered mechanical inlet in such cases.

In special cases, involving extensive washing processes, the humidity gain may be significant and require consideration.

It is important to review designs and specifications to ensure the darkroom is ventilated at a minimum rate of 10 room air changes per hour, measured as air exhausted; under negative pressure; and that all air is exhausted directly to the outside.

Sufficient make-up air must be allowed to assure proper operation of the system. If there is a possibility of accumulation of toxic vapours, i.e. if chemical tanks are located inside the darkroom, the extract fan should be wired to run continuously.

Elta Fans provide ventilation products for photo and x-ray darkrooms, so for more information, please look at examples of typical products that could be used for these applications, or alternatively, please contact us to discuss your specific application requirements.