Which strategy is designed to keep a fire from expanding?

The strategy designed to keep a fire from expanding is containment. Containment focuses on establishing boundaries to stop the fire's spread and is typically implemented when a fire has already started and efforts are being made to prevent it from exceeding specific lines. This could involve creating fire breaks, using water or fire retardant, or strategically managing resources to hold the fire in a particular area.

Offensive strategies generally involve tackling the fire head-on, which may allow it to expand if not carefully managed. Defensive strategies are more reactive and may focus on protecting exposures rather than actively preventing the spread of the fire itself. Controlled burning involves setting intentional fires to eliminate fuel and can actually be used as a preventative measure but is not specifically about keeping a fire from expanding in an ongoing incident. Thus, containment is the most fitting strategy for preventing fire expansion.