To me this seems a little far-fetched topic, but operators and vendors of photo shops constantly asked questions about the possible effects of photographic chemicals on human health. The only document that I could find - a certificate of compliance for photo-reagents of a well-known firm. Here's what could be learned from this...
When working with a paper developer should keep in mind that some of its components, in accordance with EU guidelines, is classified as an irritant that can cause irritation to the skin, as well as the corrosive agent (causes burns, harmful if it enters the gastrointestinal tract).
Please note that in addition to the general rules of the victims of the of the photochemistry, in contact with the paper in the developer gastrointestinal tract CAN NOT TAKE emetic. On some aspects of the developer set the maximum allowable concentration, so for safe operation, of course, you need ventilation, since the lack of exchange of air (requires at least 10-fold return in an hour in the working area) is recommended to use a respirator (type : sour gas).
It is necessary to avoid contact with the developer oxidants, bases, strong acids, because in reactions of this type can be released nitrogen oxides and sulfur - a very harmful substance. Also, the developer of gaseous sulfur dioxide is released which can irritate the upper respiratory tract. However, some asthmatics and people with high sensitivity can even ispytyvt difficulty breathing.
Starter developer is also not harmless - as a result of its decomposition may release noxious hydrogen chloride.
Bleach-fixer in the expansion highlights the harmful products: sulfur oxides, nitrogen oxides. In contact with strong acids may be released sulfur dioxide in the reactions with strong bases - ammonia. Moreover, harmful substances can be released upon contact with sodium hypochlorite (bleaching).
The only good news - the stabilizer is practically harmless (albeit in a puddle of it can slip and break his nose?), But even when working with the regulator should observe the rules of work with photos.