Cellulose Insulation has a Class 1 Fire rating. It is treated with fire retardants to meet all federal, state, and local fire safety requirements. The rating applies to the building assembly. Walls with cellulose insulation are one-hour (or greater) fire walls and can help control the spread of fire.
When properly installed, cellulose insulation can help reduce the spread of flames in house and building fires. Some cellulose insulation manufacturers have even qualified two and three hour firewall designs using Cellulose Insulation.