Photo Processing Hazards
in Schools

By Michael McCann, Ph.D., C.I.H. 

Photography and photographic processing are increasingly popular in junior and high schools.  This data sheet discusses the hazards of classroom photographic darkrooms and how to work safely.
Many of the chemicals used in photographic processing can cause severe skin problems and lung problems through the inhalation of dusts and vapors.  The greatest hazard usually occurs during the preparation and handling of concentrated stock solutions of the various chemicals.
Simple Black-and-White Processing

Simple black-and-white processing includes mixing chemicals, developing, stop bath, fixing, and rinsing steps.  The developer usually contains hydroquinone and Metol (monomethyl p-aminophenol sulfate), both of which can cause skin irritation and allergic reactions.  Hydroquinone may also cause eye problems and as a mutagen, might therefore be a cancer risk.  Many other developers are even more toxic.  Developers are also toxic by inhalation of the powders and ingestion, causing methemoglobinemia and cyanosis (blue lips and fingernails due to oxygen deficiency).  The developers are dissolved in a strongly alkaline solution, often containing sodium hydroxide, which can cause skin irritation and burns.  

The stop bath consists of a weak solution of acetic acid. Concentrated glacial acetic acid used to make up the stop bath can cause severe skin burns, and inhalation of even the dilute vapors can irritate the respiratory system.  Potassium chrome alum, sometimes used as a stop hardener, contains chromium and can cause ulcerations, especially in cuts and nasal membranes, as well as allergies.

The fixer often contains sodium sulfite, sodium bisulfite, sodium thiosulfate (hypo), boric acid, and potassium alum.  Hypo and the mixture of sodium sulfite and acids produce sulfur dioxide gas, especially if acetic acid is carried over from the stop bath.  Sulfur dioxide is highly irritating to the eyes and respiratory system, and asthmatics are often very sensitive to it.  Potassium alum, a hardener, is a weak sensitizer and may cause some skin irritation or dermatitis.

Advanced Black-and-White Processing

Intensification or bleaching, reduction, and toning are advanced processes in black-and-white processing.

Many intensifiers (bleaches) can be very dangerous.  The common two-component chrome intensifiers contain potassium dichromate and hydrochloric acid.  The separate components can cause burns, and the mixture produces chromic acid.  Its vapors are very corrosive and may cause lung cancer.  One common bleach, potassium chlorochromate also produces chlorine gas if heated or treated with  acid.  Handling of the powder of another intensifier, mercuric chloride, is very hazardous because of possible mercury poisoning.  Mercuric chloride is also a skin irritant and can be absorbed through the skin and should not be used.

The commonest reducer, Farmer's Reducer, contains potassium ferricyanide.  Under normal conditions, it is only slightly toxic.  However, if it comes into contact with heat, acids, or ultraviolet radiation, the extremely poisonous hydrogen cyanide gas can be released.
Many toners contain highly toxic chemicals.  These include selenium, uranium, sulfide or liver of sulfur (irritating to skin and breathing passages), gold and platinum (allergies), and oxalic acid (corrosive).  Sulfide or brown toners also produce  highly toxic hydrogen sulfide gas, and selenium toners produce large amounts of sulfur dioxide gas.

Hardeners and stabilizers often contain formaldehyde which is poisonous, irritating to the eyes, throat, and breathing passages, and can cause dermatitis.  It also causes nasal cancer in animals.  Some of the solutions used to clean negatives contain harmful chlorinated hydrocarbons.

Color Processing

There are many different types of color processes that involve a wide variety of chemicals.  In general, color processing is much more hazardous than simple black-and-white processing.  In addition to involving many of the same chemicals that are used in black-and-white processing, color processing commonly uses many other hazardous chemicals, including dye couplers (which can cause severe skin problems), toxic organic solvents, formaldehyde, and others.  Many color processes also give off more sulfur dioxide than do black-and-white processes.
Choosing Materials and Processes
    1.    Material Safety Data Sheets should be obtained for all photographic chemicals.  It is particularly important to check for hazardous decomposition products in the Reactivity Section since decomposition of fixers, toners, and other chemicals are major hazards in photography.
    2.    Because of the hazards of photochemicals, photographic processing should only be taught at the secondary school level, and not in elementary schools.
    3.    During pregnancy, only simple black-and-white processing and use of Farmer's Reducer is recommended; dry chemicals should not be mixed because of the risk of inhalation of the hazardous powdered developing agents.  Do not do toning, intensification, or color processing because of higher risks.
    4.    Toning, intensification, and color processing should not be taught, except with a few advanced students, and only if there is proper ventilation (see Ventilation section).  The only reducer allowed should be potassium ferricyanide, and care should be taken to avoid heating it, mixing it with acid, or exposing it to ultraviolet radiation.
    1.    Kodak recommends at least ten room air changes per hour of dilution ventilation for simple black-and-white processing, or 170 cfm of exhaust per work station or processor. *  I would recommend the larger of these two exhaust rates. (Fan exhaust rate in cubic feet/minute (cfm) is calculated by multiplying the room volume in cubic feet by the number of air changers/hour, and then dividing by sixty.)  The exhaust opening should be located at the rear of the sink and as close to sink level as possible.  The air should be completely exhausted to the outside and not recirculated.  Replacement or makeup air should enter the room behind the person working at the sink.
    2.    Mixing large amounts of photochemicals, toning, and color processing should have local exhaust ventilation, such as a slot exhaust hood, but not an overhead canopy hood which would draw the contaminants past the user's face.  This slot hood would have to be designed by an industrial ventilation engineer.  Without this type of ventilation, these processes should not be done.
* "General Guidelines for Ventilating Photographic Processing Areas,"  CIS-58, Eastman Kodak Company (1987).

Storage and Handling
    1.    Photographic solutions should be stored safely in clearly marked containers that are restrained so they will not fall over.  Concentrates should be stored on low shelves.  Do not store incompatible chemicals such as acids and Farmer's reducer in close proximity to one another.
    2.    Gloves, chemical splash goggles approved by the American National Standards Institute (ANSI), and a protective apron should be worn when mixing concentrated photochemical solutions to protect against skin contact.
    3.    It is preferable to use liquid chemistry rather than mixing powdered developers.  If the powders are used, small amounts can be mixed into a concentrated solution inside a glove box, or the teacher can do it while wearing a toxic dust respirator.  A glove box consists of an ordinary cardboard box, varnished on the inside for easy cleaning, with a glass or plexiglass top and two holes in the sides for insertion of arms.  If respirators are worn, all OSHA regulations concerning a respirator program should be followed.
    4.    When diluting glacial acetic acid (or other concentrated acids), always add the acid to the water, never the reverse.
    5.    Tongs should be used to handle photographic prints during printing operations so that hands are never put into the developer or other baths.  If skin contact does occur, skin should be washed copiously with water and then with an acid-type skin cleanser.  In case of eye contact, rinse for at least 15-20 minutes and contact a physician.
    6.    Cover trays when not in use, and use a funnel to pour chemicals to be reused into containers.
    7.    Dispose of small amounts of photographic solutions by pouring them down the sink.  Mixing the stop bath and developer will partially neutralize them.  Do not mix the stop bath and fixer, and flush with water for at least 5 minutes after pouring the stop bath before pouring the fixer.  If large enough quantities are involved, silver recovery might be desirable.

Safety Devices
    1.    All darkrooms should have eyewash fountains that connect to the water supply and do not need hands to operate.  In the area where concentrated developing solutions and glacial acetic acid are mixed, there should also be an emergency shower.  There should be no electric switches or electrical outlets within splash range of the shower.
    2.    All electrical outlets and electrical equipment within 6 feet of possible water splashes should be equipped with ground fault circuit interrupters.

Art Hazard News, Volume 13, No. 9, 1990

This article was originally printed for Art Hazard News, © copyright Center for Safety in the Arts 1990. It appears on nontoxicprint courtesy of the Health in the Arts Program, University of Illinois at Chicago, who have curated a collection of these articles from their archive which are still relevant to artists today.