Which of the following substances is typically not considered hazardous unless a significant spill occurs?

Milk is typically not considered hazardous unless a significant spill occurs because it is a common, everyday substance that poses little to no threat to human health and safety in normal circumstances. Unlike hazardous materials such as gasoline, paint, or asbestos, which have toxic properties or can pose serious environmental risks even in small amounts, milk is generally safe and poses minimal risks when handled appropriately.

Even in the event of a spill, while milk may create a slippery surface, it does not have the harmful health effects associated with the other substances listed. A significant spill of milk could lead to local environmental concerns, such as affecting water quality in aquatic systems, but it does not present the immediate risks related to fire hazard, toxic fumes, or long-term health effects that the other options imply. Thus, milk stands out as non-hazardous in ordinary situations compared to the other substances.