Perhaps we shouldn't joke about it, but deadly though some cyanides are,
the LD50 is of the same order of magnitude as many other chemicals we use
with little or no thought for safety. There are many substances with
cyanide in the name that are relatively harmless - for example potassium
ferricyanide.
Cyanide is a regular part of the diet - in low dosage - in those African
countries where cassava is a part of the diet (washing is necessary in
the preparation to remove most of it). Although harmless in small
quantities repeated dosing is thought to cause deafness an problems with
walking.
Cyanides are - or certainly used to be - used in very large quantities in
various industries, including electroplating. It used to be common
practice for workers to put their hands into the baths. Deaths were
exceedingly rare. When they were used as photographic fixers there were
some fatalities, but I think only when people working in the dark mistook
the fixer for their glass of beer and took a good swig before realising
their mistake. I seem to recall reading a Bill Jay article called 'Death
in the Darkroom' or something similar.
One good point about cyanides is that they are not cumulative. If you
ingest a quantity below the lethal dose it will fairly rapidly be lost
from the body. Much more dangerous to those involved in photography and
alt-processes are the heavy metals which do build up.
Peter Marshall
On Fixing Shadows and elsewhere:
http://www.people.virginia.edu/~ds8s
Family Pictures, German Indications, London demonstrations &
The Buildings of London etc: http://www.spelthorne.ac.uk/pm/