According to Bob Blanda, owner of Mill Bergen Pool Center in Brooklyn and president of the Northeast Pool and Spa Association (NESPA), the problem with the drain covers in most commercial pools and spas is their shape; they’re flat, flush with the bottom of the pool. If an object occludes the drain, the suction is amplified, and may be strong enough to trap someone under the surface. It’s also possible for a swimmer’s hair to become entangled in certain types of drain, or even for a victim to be eviscerated by extreme drain suction.
Full article here: http://cooperator.com/