Coverings and linings must have a flame spread index not more than 25 and a smoke development index not more than what?

Coverings and linings in buildings are subject to specific fire safety standards to minimize the risk during a fire. The flame spread index measures how quickly flames propagate across the material's surface, while the smoke development index assesses the amount of smoke produced when the material burns.

For the smoke development index, a value not exceeding 450 is generally acceptable for many applications. However, in some contexts, particularly regarding occupancy and specific building codes, a maximum smoke development index of 50 is a common standard for certain applications, especially in areas where rapid evacuation is crucial. This standard aims to ensure that the smoke produced during a fire is limited to improve visibility and reduce inhalation hazards for occupants.

Thus, having a smoke development index that does not exceed 50 is essential for enhancing fire safety and ensuring compliance with regulations that aim to protect life and property.