http://www.amerexfireextinguishers.com/Halotron1_MSDS_1_.pdf
"Use of this material in confined spaces when personnel are present is acceptable only if the volume of the space is sufficiently large"
"Inhalation of high concentrations of vapor may cause central nervous system effects such as dizziness, drowsiness, anesthesia, or unconsciousness"
"At concentrations of 20,000 ppm or higher, HCFC-123 may causes increased sensitivity of the heart to adrenaline which might cause irregular heart beats and possible ventricular fibrillation or death"
"Eye contact:
May cause irritation, tearing, or blurring of vision, which result in part due to the cooling effect of HCFC-123 evaporation"
That's Halotron, one of the Halon replacements. Good for some things, not so good for others.
Here is the MSDS for Halon 1301:
https://kidde-fenwal.com/Media/MSDS/Fenwal_Halon1301_02092012.pdf
The main risk is from freezing your fingers off if you get hit by the stream.
Inhalation 1-hour LC50(rat) >770,000 ppm (that's 77%!)
Here is the MSDS for Halon 1211:
http://www.wfrfire.com/MSDS/pdf/halonMSDS.pdf