The Problems:

•	Heat
•	Condensation
•	Fumes
•	Body Odours
•	Tobacco Smoke

Solutions:

DARKROOMS : Air change rate per hour 10-15

Because of the necessity to exclude light, all natural ventilation is also excluded. 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.

Darkroom models are designed to provide extract ventilation without letting in light. They may be installed through blacked out windows, roofs, and through walls. They normally consist of a fan with an external roof cowl, together with an extra internal matt black cowl.

Internal darkrooms may be ventilated to outside atmosphere using ducting and accessories. In general, units should be sited as close as possible to the local source of fumes, such as developing baths. Some chemicals are heavier than air and benefit from an extract point between bench and head height.

Adequate air replacement is necessary to ensure correct functioning of the unit and to avoid air being drawn in from the wrong sources (i.e. "through-the-wall" continuous developing machines), with possible degradation of print quality. The air replacement source should be as far away as possible from the unit and should be light-tight. Non-vision grilles, black finish, are available as ventilation accessories. Because darkroom conditions vary, controllers should be included to enable the ventilation rate to be adjusted. If dust is a problem, suitable filters can be fitted to ducted air replacement systems or internal transfer grilles. Ensure that the scheme complies with relevant local authority by-laws and fire regulations.

Size and Number of Ventlation Units

Calculate the volume of the room (height x width x length) and multiply by ACH. This equals the minimum volume required per hour. Choose the size and number of units from the output table to ensure that this minimum volume is achieved.