Which of the following actions will help prevent a chain reaction in fire?

Excluding oxygen is a fundamental method for preventing a chain reaction in fire. Fire requires three elements to sustain combustion: heat, fuel, and oxygen, often referred to as the fire triangle. By removing or limiting the availability of oxygen, the combustion process cannot continue, effectively interrupting the chain reaction that fuels the fire. This approach is commonly utilized in fire suppression strategies, such as foam application or the use of fire blankets, which smother the flames by cutting off their oxygen supply.

In contrast, adding more fuel, increasing temperature, or improving ventilation would likely enhance the fire's intensity and facilitate the continuation or expansion of the combustion process. These actions could exacerbate the situation rather than prevent a chain reaction, reinforcing the importance of oxygen exclusion as a critical tactic in fire prevention.