An actual or potential fire situation exists and the life hazard exceeds the rescue capabilities of initial alarm companies.

The number, location and condition of actual victims exceeds the rescue and removal capabilities of companies.

An actual or potential fire situation exists and the property protection demand (both internal and external) exceeds the fire control
capabilities of initial alarms companies.

Fire conditions become more severe or the situation deteriorates significantly.

All companies have been committed and the fire is not controlled.

Forces are depleted due to exhaustion or injury or are trapped or missing: command must forecast the affect the fire will have
personnel and provide for the support of such personnel in advance.

Command runs out of some resources (men, apparatus, water, equipment, command, etc.)

There is evidence of significant fire but companies are unable to determine location and extent.

Companies cannot effectively perform early salvage operations.

Situation becomes so widespread/complex that command can no longer effectively "cope" - the situation requires larger command
organization and more operational functions.

Command instinctively feels the need to summon additional resource-(do not disregard fireground hunches)

Weather conditions also play a part in additional resources. Hot, humid and cold weather all lead to early depletion of a firefighter's
physical capabilities.