Tanks at a facility that have been spaced according to NFPA 30 are less likely to cause:

When tanks at a facility are spaced according to the National Fire Protection Association (NFPA) 30 guidelines, they are positioned in a manner that minimizes the risk of fire spread and heat transfer between them. This spacing requirement is crucial in preventing scenarios like boil over or direct fire from one tank affecting another.

Boil over can occur in tanks containing flammable liquids, where excessive heat can cause a violent eruption of the liquid, leading to catastrophic consequences such as fires and explosions. By ensuring that tanks are sufficiently distanced from one another, the likelihood that a fire from one tank could ignite another is significantly reduced. This spacing acts as a buffer that helps contain such risks, thus decreasing the chances of multiple tanks catching fire or experiencing boilover, which enhances overall safety at the facility.

This reasoning clarifies why the correct option reflects the benefits of appropriate spacing in terms of reducing fire hazards associated with nearby tanks.