Mich. Comp. Laws § 29.21b: Fire extinguishers; liquefied compressed gas, toxicity.

Sec. 21b.

Notwithstanding section 21a, a liquefied compressed gas extinguishing agent that meets both of the following conditions of toxicity and use may be used in properly engineered fire extinguishing or fire control systems:

(a) The agent in its normal state is not a prohibited agent or propellant under section 21a(1).

(b) The agent is used only under conditions approved by the national fire protection association and a nationally recognized independent testing laboratory that has considered the hazard of the thermal decomposition products and use approved by the bureau.