Which construction type is least likely to provide safety against fire?

Type 5 construction is typically the least fire-resistant among the various construction types. This classification generally encompasses lightweight materials such as wood and is often characterized by the use of standard wood framing techniques. Because the materials are less robust and do not have significant fire-retardant properties, structures built with this type are more susceptible to rapid fire spread.

In contrast, Type 1 construction, featuring non-combustible materials, provides the highest level of fire resistance, designed to withstand prolonged exposure to fire. Type 2 construction, while also non-combustible, may not provide the same level of protection as Type 1 but still limits fire spread effectively. Type 4 construction, known for its heavy timber, combines substantial mass with a degree of fire resistance, as the larger timbers char on the outside when exposed to flames, slowing the fire's progression.

Given the characteristics of these different construction types, Type 5 is the least likely to provide safety against fire due to its vulnerability to burning and the lack of inherent fire-resistive materials.