To prevent dangerous suction effects, the main drain grate should be how much larger than the discharge pipe?

The correct answer indicates that the main drain grate should be four times larger than the discharge pipe to effectively prevent dangerous suction effects. This requirement is fundamental in ensuring the safe operation of pools and spas. A larger grate area reduces the velocity of water flow, which minimizes the risk of creating a strong suction that can lead to entrapment.

When the grate is significantly larger than the discharge pipe, it allows for more surface area for water to enter, hence reducing the risk of blocking and the associated dangers of suction. This is particularly crucial in environments where individuals may be swimming or playing, as it helps enhance safety features.

In contrast, the other options suggest diameters that may not sufficiently mitigate the suction risks. For example, if the grate were only two or three times the size of the discharge pipe, it may not be adequate to ensure the safety that four times provides. Therefore, specifying a size ratio of four times is critical for promoting a safe aquatic environment.