The Pool Safety Council has released two studies examining the
dynamics of limb and evisceration entrapments, and the role safety
vacuum release technology might play in preventing or mitigating
The Washington, D.C.-based organization was founded, and is led by,
Paul Pennington, former president of Vac-Alert Industries, a
leading manufacturer of SVRS systems.
“I think the study supports our position that we’ve had
all along that the SVRS prevents against limb entrapment,”
Pennington said. “I think it shows that it’s a good
idea to have an SVRS to prevent evisceration because it might stop
the worst-case scenario.”
Currently, many contend that SVRS technology prevents body
entrapments, but not the other four types — limb,
evisceration, hair and mechanical.
PSC sought to re-explore this belief in the case of limb entrapment
and evisceration. The organization collaborated on two studies with
the NASA-funded Space Alliance Technology Outreach Program and the
Florida Institute of Technology.
The studies were performed over the summer by Florida Tech
professor Steven M. Jachec, Ph.D., P.E. He applied engineering
equations and information taken from previously published articles,
journals and studies. Some physical testing was performed by PSC
The first study examined limb entrapment and the role of suction in
causing it. With the application of equations, Jachec examined the
first part of a suction limb entrapment — when the limb is
initially drawn into the outlet. As this happens, the study showed,
the limb is pulled inward by forces stronger than most people can
“The study shows that the pull can be quite large and beyond
what a little one could overcome,” said George Pellington,
PSC’s technical director and current Vac-Alert president.
“The flow and suction are like a tractor beam pulling the arm
This leads PSC officials to believe some type of vacuum release
system would help during this initial part of the entrapment.
Future studies would have to explore what happens once the limb
causes a seal in the pipe, Pellington added.
Also requiring more study is a PSC theory regarding how
suction-related entrapments occur.
One belief held by many, including the Association of Pool & Spa Professionals,
states that when a limb becomes trapped in a pipe, it often swells,
causing the body part to become stuck and create a mechanical bond
with the pipe. In these cases, releasing the suction will not help
because the limb is wedged in too tightly, according to APSP
But PSC theorizes that such swelling may occur because the vacuum
causes pressure inside the limb to be higher than that inside the
pipe. Once the vacuum is broken and pressure equalizes, PSC
believes, the limb would immediately become free.
“[I believe] that APSP’s assumption is too
simplistic,” Pellington said. “What’s happening
is a sudden blood rush to the area … which causes a swelling
like a mechanical inflation. Then, once the vacuum is off, the arm
comes out really quickly.”
PSC officials said case studies suggest that most limb entrapments
are suction-related, as opposed to mechanical, and could be
mitigated by SVRS technology. “All known U.S. limb entrapment
cases [but one] have reported release of the bather once the
suction force was released,” Pellington stated.
For the next study, addressing evisceration, the Pool Safety
Council and Jachec sought to establish how long it takes for an
evisceration to occur. Jachec referred to previously recorded data
and literature, concluding that the fastest an evisceration could
take place is 1.86 seconds. However, the tissue could begin tearing
and evisceration begin as quickly as 0.44 seconds.
Jachec performed a related analysis to determine how quickly an
SVRS can react. Using data supplied by PSC, he computed a time of
1.23 seconds. The evisceration and SVRS reaction times both applied
to a scenario involving a 3-horsepower pump, 50 feet of 2-inch
schedule 40 PVC plumbing, and 70 gallons per minute of flow.
Some of the data was drawn from testing that took place at
PSC’s 5,000-square-foot testing facility near Tampa,
“This brings up the question of which would you rather have
— a pool that has no protection or one that has an SVRS
— when you’ve got your children or grandchildren
… playing in the pool? I think it’s a
no-brainer,” Pennington said.
However, SVRS reaction time is affected by variables such as length
of pipe and the technology involved. Reaction times as high as 4.5
seconds are accepted for compliance with ASME A112.19.17-2002
— far longer, in relative terms, than the study’s
1.86-second time frame for an evisceration to occur.
Others involved in writing entrapment-prevention standards get
nervous at the idea of claiming a technology can protect against
evisceration when it only helps in an unknown percentage of
This concern comes from the fact that eviscerations happen so
quickly and do so much damage. Even partial evisceration leads to
devastating injuries and, sometimes, death. Because of this, some
believe only devices that prevent it from starting altogether
should be considered protective measures.
“The fact that some percentage of them could be helped, some
percentage could be mitigated and others there’s nothing that
can be done [isn’t enough],” said Steve Barnes, head of
APSP’s Technical Committee and product manager, safety and
compliance, at Pentair Water Pool and Spa. “We draw the line
at the side of safety that says, ‘We’re not going to
pick and choose. We’re going to prevent.’”
But there is one thing that both sides agree on — more
research is needed.