Vessels operated at or in excess of the temperature of volatilization of toxic metals, alloys or compounds which generate dangerous air contaminants shall be provided with local exhaust ventilation. Vessels used for melting or cleaning such metals, alloys or compounds shall be provided with exhaust ventilation when operated in such a manner as to generate dangerous air contaminants. The combustion chamber, when operated in such a manner as to release dangerous air contaminants, shall be provided with local exhaust ventilation.