I don't mean to belittle anyone, but this question comes up so often with no substantiated evidence. Discharge is not a carcinogen, it does not give you cancer, you do not die from it. It is not regulated by the federal government, or by D.O.T. for shipping.
Discharge is not a new process and has been around for quite some time. People have been printing it for years.
The active chemical is a compound called "ZFS" and contains a negligible amount of free flowing formaldehyde. You aren't actually screen printing formaldehyde. To make a comparison, fluorine is an extremely dangerous poison, yet we brush our teeth with a compound called Sodium Fluoride.
In regards to the smell, the exhaust of discharge is an irritant to the eyes and proper ventilation should ALWAYS be taken when printing shirts regardless if your printing discharge or not.
It is good that you are concerned for the safety of your shop, but as mentioned above, there are many more serious threats to your safety in your shop and usually under your kitchen cabinet.
I hope this clears the air for some of the misconceptions regarding discharge. Feel free to fire any questions back.