I teach
aquatic safety — suction outlet entrapment avoidance, to be exact In
reading the article in the Feb.29th issue (“Bill Proposes Change to
California Pool Law, page 12), I saw a photo of an anti-vortex main
drain cover. The caption under that photo stated “Legal
glitch":Currently, a California law requires an anti-entrapment drain
cover be added when any home improvement permit is pulled. The photo
would lead one to believe the cover shown to be a anti- entrapment type
cover, that is indeed a misnomer. The photo is an anti-vortex type
cover, (I do understand the term “journalistic license.”)
Perhaps I can help make this more clear by explaining the difference
between the two different items. Please note: This could be a matter of
a safe dual drain system or a deadly dual drain system.
Back in the early 1970s, due to the advent of closed impellers and
self-priming pumps, more powerful suction outlets and main drains came
out. To prevent air from being entrained into the main drain via a
vortex, anti-vortex main drain covers were developed
— not so much to protect children, but to protect pump shaft seals and
motors. Safety was not the issue because suction entrapment was not “in
the news” at that time.
One of the criteria of the anti-vortex cover was “a small open
surface area” perhaps 10 square inches or less. These covers did,
indeed, protect pump motors and the related seals, but not children. The
turbulent area around the small open surface area created a high
velocity that could pull in hair or bathing suit ties, etc., and in some
cases harbored a finger entrapment potential.
Then in the late 1970s, we had child injuries and worse incidents making
the news. Finally, in 1995, the first child anti-entrapment type cover
was invented. The inventor (Harry Newhard) realized a larger open
surface area meant less velocity and a slower flow rate through the
cover would prevent hair entanglement. His invention was deemed an
“anti-entrapment type main drain” cover because it was created to reduce
child entrapment injuries or worse.
Also in the late 1970s, studies were being done to use dual drain
technologies to prevent child entrapment. These tests were done mostly
on 12 inch by 12 inch main drains. The individual could “roll off’ the
96-square-inch open surface area and release himself. Remember, we are
dealing with open surface area, not overall area. Open surface area on
some 12-by-12-inch grates measures 96 square inches, and the overall
area of 144 square inches. More testing should have been done with
smaller sumps.
Now 2007 arrives and we’re recommending hydraulically balanced dual
drains separated by a minimum of 3 feet. Unfortunately, this may not be
as safe as it seems. It is important we remember the “small open surface
area” of some covers.
Here is an example: We have a code-compliant dual drain system; we also
have two ANSI/ASME 112.19.8 Standard-certified anti- vortex drain covers
with a
small open surface area of approximately 8 inches, Now, for whatever
reason, one drain cover becomes missing or dislodged. That open main
drain pipe or sump can now have a hold-down force that could preclude a
child’s escape. In other words, he is trapped to the forces from the
pump suction under him and the weight of the water above him as well,
the opposing drain cover (still intact) is allowing the pump to maintain
a full head and hold the child to the unprotected suction outlet. A bad
scenario, I know.
To recap: 1970 main drain cover, 1980 anti-vortex cover, 2000
anti-entrapment cover and now 2007 anti-entrapment type suction outlet
cover
As we build more and more dual drain systems, we need to understand the
hydraulics involved. It would be far more beneficial to install large
open surface area anti-entrapment type suction outlet covers to minimize
the related suction hazards as well as allowing the pumps to operate
with more fluid volume at a lower velocity. (Note: The connecting pipe
between the dual drain sumps should be 2.5 inches in diameter or larger,
not to exceed 6 feet in separation to avoid high hold-down forces.)
Bottom line: It boils down to child safety. We need to focus on
protecting children, and understand how systems and products relate to
each other — not just blindly install systems and products without
understanding the reasoning behind their development or effects after
installation and operation. We require education to be effective in our
safety related efforts.
Thank you for promoting child aquatic safety. Please keep up the good
work and, perhaps increase your photo budget.
