This publication represents a basic standard for safe operation, substantial and durable construction, and acceptable performance of ventless firebox enclosures for gas-fired decorative type unvented room heaters. It is the result of years of experience in the manufacture, testing, installation, maintenance, inspection and research on unvented gas-fired heating appliances designed for the utilization of gas. There are risks of injury to persons inherent in some appliances that, if completely eliminated, would defeat the utility of the appliance. The provisions in this Standard are intended to reduce such risks while retaining the normal function of the appliance.