In black-and-white photographic processing, exposed film or paper is removed from a light-tight container in a darkroom and sequentially immersed in trays containing aqueous solutions of developer, stop bath and fixer. After a water washing and drying, the film or paper is ready for use. The developer reduces the light-exposed silver halide to metallic silver. The stop bath is a weakly acidic solution that neutralizes the alkaline developer solution and stops further reduction of the silver halide. The fixer forms a soluble complex with the unexposed silver halide, which, together with various water-soluble salts, buffers and halide ions, is subsequently removed from the emulsion in the washing process. Rolls of film are usually processed in closed canisters to which the various solutions are added.
Potential health hazards
Because of the wide variety of formulae used by various suppliers, and different methods of packaging and mixing photoprocessing chemicals, only a few generalizations can be made regarding the types of chemical hazards in black-and-white photoprocessing. The most frequent health issue is the potential for contact dermatitis, which most frequently arises from skin contact with developer solutions. Developer solutions are alkaline and usually contain hydroquinone; in some cases they may contain p-methylaminophenolsulphate (also known as Metol or KODAK ELON) as well. Developers are skin and eye irritants and may cause an allergic skin reaction in sensitive individuals. Acetic acid is the principal hazardous component in most stop baths. Although concentrated stop baths are strongly acidic and may cause skin and eye burns following direct contact, the working-strength solutions are usually slight to moderate skin and eye irritants. Fixers contain photographic hypo (sodium thiosulphate) and various sulphite salts (e.g., sodium metabisulphite), and present a low health hazard.
In addition to potential skin and eye hazards, gases or vapours emitted from some photoprocessing solutions may present an inhalation hazard, as well as contribute to unpleasant odours, especially in poorly ventilated areas. Some photochemicals (e.g., fixers) may emit gases such as ammonia or sulphur dioxide resulting from the degradation of ammonium or sulphite salts, respectively. These gases may be irritating to the upper respiratory tract and eyes. In addition, acetic acid emitted from stop baths may also be irritating to the upper respiratory tract and eyes. The irritant effect of these gases or vapours is concentration dependent and is usually observed only at concentrations that exceed occupational exposure limits. However, because of a wide variation in individual susceptibility, some individuals (e.g., persons with pre-existing medical conditions such as asthma) may experience effects at concentrations below occupational exposure limits. Some of these chemicals may be detectable by odour because of the chemical’s low odour threshold. Although the odour of a chemical is not necessarily indicative of a health hazard, strong odours or odours that are increasing in intensity may indicate that the ventilation system is inadequate and should be reviewed.
The key to working safely with photoprocessing chemicals is to understand the potential health hazards of exposure and to manage the risk to an acceptable level. Recognition and control of potential hazards begins with reading and understanding product labels and safety data sheets.
Avoiding skin contact is an important goal in darkroom safety. Neoprene gloves are particularly useful in reducing skin contact, especially in mixing areas where more concentrated solutions are encountered. Gloves should be of sufficient thickness to prevent tears and leaks, and should be inspected and cleaned frequently—preferably thorough washing of the outer and inner surfaces with a non-alkaline hand cleaner. In addition to gloves, tongs may also be used to prevent skin contact; barrier creams are not appropriate for use with photochemicals because they are not impervious to all photochemicals and may contaminate processing solutions. A protective apron, smock or lab coat should be worn in the darkroom, and frequent laundering of work clothing is desirable. Protective goggles also should be used, especially in areas where concentrated photochemicals are handled.
If photoprocessing chemicals contact the skin, the affected area should be flushed as rapidly as possible with copious amounts of water. Because materials such as developers are alkaline, washing with a non-alkaline hand cleaner (pH of 5.0 to 5.5) may aid in reducing the potential to develop dermatitis. Clothing should be changed immediately if there is any contamination with chemicals, and spills or splashes should be immediately cleaned up. Hand-washing facilities and provisions for rinsing the eyes are particularly important in the mixing and processing areas. If concentrated or glacial acetic acid is used, emergency shower facilities should be available.
Adequate ventilation is also a key factor to safety in the darkroom. The amount of ventilation required varies according to room conditions and processing chemicals. General room ventilation (e.g., 4.25 m3/min supply and 4.8 m3/min exhaust, equivalent to ten air changes per hour in a 3 x 3 x 3 m room), with a minimum outside air replenishment rate of 0.15 m3/min/m2 floor area, is usually adequate for photographers who undertake basic black-and-white photoprocessing. The exhaust air should be discharged outside the building to avoid redistributing potential air contaminants. Special procedures such as toning (which involves the replacement of silver by silver sulphide, selenium or other metals), intensifying (which involves making parts of the image darker by the use of chemicals such as potassium dichromate or potassium chlorochromate) and mixing operations (where concentrated solutions or powders are handled) may require supplementary local exhaust ventilation or respiratory protection.
There are a number of colour processes that are more complex and also involve the use of potentially hazardous chemicals. Colour processing is described in the chapter Printing, photography, and reproduction industries. As with black-and-white photoprocessing, avoiding skin and eye contact and providing adequate ventilation are key factors to safety in colour processing.