What is the critical consideration when dealing with an electrical underground vault fire?

The critical consideration when dealing with an electrical underground vault fire is to contact utility personnel for guidance. This is because underground vaults often contain live electrical equipment and wires, which pose significant risks to firefighters if not handled properly. Utility personnel have the expertise and knowledge of the electrical systems in the area, and they can provide essential information regarding the status of the power supply, potential hazards, and the safest methods for extinguishing the fire without causing further harm or danger.

Water, for example, may not be suitable for extinguishing an electrical fire due to the risk of electrocution and potential for electrical discharge. Similarly, while evacuation may be necessary in some scenarios, it's essential to understand the full situation before taking such actions. Waiting for the fire to burn out is not a safe or strategic approach given the risks involved with underground electrical systems. Engaging with utility experts ensures that the situation is managed safely and effectively.