The borate treatment gives the cellulose insulation a very high fire safety rating in terms of combustibility. From a safety standpoint, that’s good news. As a line firefighter trying to deal with a fire in cellulose insulation, that’s not so good news. The low combustibility of the cellulose makes it easy for fires to start, but the fire retardant treatment doesn’t allow them to grow quickly, so they can continue to smolder. Dealing with a smoldering fire in cellulose insulation in attics and walls can be very challenging for firefighters, because our newer technology isn’t always reliable when investigating these fires.
When cellulose insulation burns in an attic space or within a wall, it typically burns from the bottom up, and it burns at such low temperatures that even the best thermal imaging camera (TIC) may not pick up the traces of heat. Additionally, when the insulation is blown in, it makes a thick blanket that can hide the signs of fire. So, at first glance, it can be difficult to tell that a fire is even burning.
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.