Which type of stairs loses tension rapidly when exposed to heat?

Folding stairs are constructed in a way that makes them particularly susceptible to rapid loss of tension when exposed to heat. This is primarily due to the materials used in their construction, which often include lightweight metals or alloys that can lose structural integrity at elevated temperatures. In a fire scenario, the heat can cause these materials to weaken quickly, leading to a potential collapse or failure of the stairs.

Understanding the properties of materials under heat stress is crucial for safety in fire situations. Firefighters must be aware that folding stairs can not only lose tension but also may not provide safe egress for individuals, which can contribute to dangerous situations during evacuations or rescues. The other types of stairs listed—spiral, scissor, and circular—generally have different designs and construction methods that allow them to maintain their structural integrity better under heat, making them less problematic in fire scenarios compared to folding stairs.