In which scenario would using water directly on the cylinder be recommended?

Using water directly on the cylinder after the fire has been extinguished is considered the safest and most effective approach to cool the cylinder and prevent further incidents. In the aftermath of extinguishing a fire, residual heat from the cylinder can pose risks such as an explosion or a resurgence of fire if the temperature remains elevated. Cooling the cylinder with water reduces the thermal load, helping to stabilize the situation while ensuring that any remaining flammable substances within the cylinder are kept at a safe temperature. This process is critical in managing potential hazards and ensuring the safety of the surrounding environment and firefighting personnel.

In contrast, it would not be advisable to use water directly on a cylinder when a fire is small and controllable, since other methods might effectively manage that specific situation without introducing vulnerabilities. Similarly, applying water only if no other options are available does not consider the proactive measures needed when dealing with potentially hazardous materials. Preparing for a BLEVE (Boiling Liquid Expanding Vapor Explosion) involves different strategic responses, and directly applying water at that moment can be extremely dangerous rather than a standard procedure.