Which material should not be used for a fire stop?

Particle board is not an appropriate choice for use as a fire stop due to its composition and structural characteristics. Fire stops are materials designed to slow down or stop the spread of fire and heat through concealed spaces in a building. Effective fire stop materials are typically non-combustible or have a higher fire resistance, which particle board does not typically provide because it is made from wood chips and adhesive, making it more combustible than other options.

In contrast, materials like plywood and solid lumber can provide better structural integrity and fire resistance when properly installed. Plywood, for example, has a generally higher density and can withstand fire better than particle board. Similarly, two pieces of lumber or nominally thicker lumber generally have superior performance characteristics regarding fire resistance due to their mass and solid structure.

Thus, the use of particle board as a fire stop could compromise safety, making it unsuitable for this particular application.