Cardiac arrhythmias and blood levels associated with inhalation of Halon 1301

In this study we determined airborne concentrations of Halon 1301 (CBrF3) and the associated blood levels which produce cardiac arrhythmias in dogs. Beagle dogs were exposed by inhalation to Halon 1301 concentrations ranging from 5 to 20% and, after five minutes of exposure, were given epinephrine by intravenous injection (8--10 micrograms/kg). Electrocardiograms were recorded. Serious cardiac arrhythmias were produced with concentrations of 7.5% or greater. A second group of dogs with cannulas surgically implanted in the common carotid artery and external jugular vein were exposed to 5%, 7.5% and 10% Halon 1301 for 60 minutes. The blood concentration of Halon 1301 increased rapidly during the first five minutes of exposure, plateaued within twenty minutes, and declined rapidly after exposure. The mean blood concentrations at equilibrium were directly proportional to airborne concentrations: at a concentration of 5% in air -- arterial 19.2 micrograms/mL, venous 14.6 micrograms/mL; at 7.5% in air -- arterial 30.6 micrograms/mL, venous 28.4 micrograms/mL; and at 10% in air -- arterial 402 micrograms/mL, venous 32.1 microgram/mL. Since there was no rapid increase in blood fluorocarbon concentration after the first five minutes of exposure, it does not seem likely that risk of cardiac sensitization would increase with increased length of exposure to a given concentration.