An inexpensive category of flame retardant is actually introduced to the plastic for a different reason. Many plastics are manufactured with as much as twenty percent filler. The most common filler is calcium carbonate and another is talc. The calcium carbonate is added to make the production of the plastic less expensive, but it does have the added benefit of providing some flame retardant properties.

The way that the dilution agent works as a flame retardant is that is lowers the percentage of combustible material in the finished product. If there is less combustible material then there is less fuel for the fire. Less fuel means it could burn itself out more quickly. Hence and unsurprisingly, the industry calls this method of fire protection dilution of fuel.

There are two main types of intumescents, soft char producers and hard expanding char producers. The soft char producers are poor heat conductors and often contain hydrates. In the previous post, I talked about how hydrates can be flame retardants in their own right due to their endothermic degradation. Once the hydrates have decomposed, the soft intumescent insulates the good material from the open flame. Hard expanding producers are just what they sound like. They produce a very hard and substantial char that will literally not let the fire through.

Soft chars are appropriate for spray fireproofing or firestop pillows that are stuffed into holes in wall or floor assemblies. Hard expanding chars are used for plastic pipe firestops and fireproofing of exterior steel structures. They are used here because you need a firestop that is capable of handling expansion pressure.