Every day, aquatics professionals choose and install safety vacuum release devices. Their daily reality is far from the I-Codes,
testing labs, Virginia Graeme Baker Pool and Spa Safety Act,
Consumer Product Safety Commission, and the often
bitter rivalries and political battles that have surrounded these
products in recent years. Beneath the endlessly evolving seesaw of
power and influence, those in the field are simply trying to do
their jobs, understand the technology and comply with the
But how exactly does that technology function?
Getting beyond the controversy to examine the actual workings of
secondary vacuum-releasing devices is no small feat. Nevertheless,
it’s critically important that those handling the products
know what they do, their strengths and limitations, and the
questions yet to be answered.
Safety vacuum release systems and automatic pump shut-offs —
which many refer to collectively as SVRS’s — are two of
the secondary options listed in the Virginia Graeme Baker Act.
Generally, the systems are designed for single outlets and
potentially incorrectly installed multi-outlet systems (that is,
the drains are less than 3 feet apart, or one has been blocked
during plastering). Both offer an efficient and straightforward
method of retrofitting existing pools and spas of this type.
An SVRS, as distinguished from an automatic pump shut-off, works
like this: Whenever the device senses a vacuum increase over a
particular threshold, it releases a valve, which allows air into
the line, causing the pump to cavitate and the vacuum to break. The
sensitivity of a given product depends on its “window,”
the pressure differential allowed before the valve is opened.
Depending on the model, SVRS’s may be installed in a number
of locations throughout the circulation system. To conform with
VGBA, as well as many state and local codes, SVRS’s must be
tested and certified to comply with ASME A112.19.17.
According to the standard, SVRS devices must be able to function
within a specified period of time (from the initial blockage of a
single outlet until the trapped person is freed), calculated based
on the plumbing schematic involved. The longest allowable span is
4.5 seconds through 200 feet of pipe. Some manufacturers claim
their products work in approximately 1 second under certain
An automatic pump shut-off is an electrical device designed to
literally shut off the pump any time it discovers an irregularity;
this is detected through monitoring pressure and vacuum or drops in
the pump’s power usage.
Whereas an SVRS works by adding air into the line, an automatic
pump shut-off disengages the extremely low pressure that causes a
vacuum to occur. Once the pump is off, the pressure equalizes,
thereby dissipating the vacuum. Some manufacturers state that this
happens almost instantly.
To sense an entrapment, some automatic pump shut-offs monitor
pressure, while others look for a dramatic drop in the pump’s
power usage. Currently, the VGBA doesn’t require automatic
pump shut-offs to meet the ASME A112.19.17 standard;
however, to gain third-party certification, virtually all do.
Some products combine the function of an SVRS with an automatic
pump shut-off, meaning the device introduces air into the line as
well as shuts off the pump.
With any of these technologies, one drawback is the potential for
nuisance tripping, which happens when a device is mistakenly
activated. SVRS's and automatic pump shut-offs must walk the line
between detecting when pressure or electrical output has dropped
low enough to indicate entrapment, yet continuing to function
during the pressure and power differentials that occur every
Individual models vary in sensitivity — some are designed to
trip at pressure drops of as little as 2 inches of mercury, while
others withstand up to 12 or 13.
Industry professionals also have seen nuisance tripping happen when
the circulation system is initially activated. “There’s
a kick when the pumps are starting up, and that draws the vacuum
down so much just on the initial start — just to get the
momentum of the water going — that it would trip the
unit,” says David Peterson, president/CEO of Watershape
Consulting, based in San Diego.
To check for potential nuisance trips, installers can simulate a
“Close valves gradually vs. completely, and just try to get a
sense for what happens to the unit,” says Scott Petty,
product manager, pumps, at Hayward Pool Products in Elizabeth, N.J.
“Get a sense of ‘If I slowly close this, is it going to
make a difference?’”
To minimize nuisance tripping, some manufacturers have added an
automatic reset function that allows the pump to start again,
provided the pressure or power load is back to normal after a
specified number of minutes. At least one system has a function to
differentiate between the sudden pressure change that occurs during
an entrapment, and those that take place gradually, such as when a
filter accumulates dirt.
When do secondary devices make the most sense?
Local code requirements aside, industry professionals agree that
these products are most needed in single-drain pools or vessels
that function that way, meaning the outlets are less than 3 feet
apart or, for some reason, one is not working.
What about the larger pools often found in waterparks and other big
commercial venues? At present, the ASME A112.19.17
standard only stipulates testing the performance of SVRS’s
and automatic pump shut-offs on smaller, single-drain systems
designed with 2-inch pipe, says Steve Barnes, chairman of APSP’s Technical Committee, and the safety and
compliance manager for Sanford, N.C.-based Pentair Water Pool and
Though the Standard Writing Committee began exploring methods to
determine SVRS functionality on multidrain systems and single-drain
systems with skimmers recently, the standard does not test for
“What you really have to do is look at the specific
system,” Barnes adds. “The focus has to be on the
However, an entrapment hazard could still exist in a pool with
multiple drains, if the installer undersized the plumbing.
“If you remove the cover and put your hand in the pipe, there
may be quite a bit of hold-down force there,” Peterson says.
“Because the plumbing is undersized, you may have quite a bit
of vacuum drawing, even though it’s a split pair. In that
case, a backup device would help.”
Can SVRS’s save lives?
There’s widespread agreement that SVRS devices can save lives
in certain situations — the devices are effective in
preventing body entrapment, not hair or mechanical entrapment
— but there’s still dissension over whether they
satisfactorily guard against the other two modes of entrapment
(evisceration and limb).
Though extremely rare (there were only two known cases between 1999
and 2009), evisceration is gruesome to the point of being
unthinkable. It also is the fastest to occur, with time estimates
ranging from 0.25 to 1.86 seconds, depending on factors including
the victim’s size, age and gender.
The ASME standard allows backup devices to take as long as 4.5
seconds to stop the vacuum in certain scenarios. But in the case of
evisceration, even a fraction of a second can be crucial.
Additionally, site-specific conditions such as pipe length/size and
pump horsepower will affect response time.
For this reason, the Association of Pool & Spa Professionals adamantly
stands against claiming that any technology will mitigate an
evisceration once a vacuum is formed. “It’s just
unacceptable, and any public policy promotion based on that premise
has been rejected by ICC, ANSI, APSP and ASME,” Barnes
But the Pool Safety Council, an organization founded and run by the
former president of one of the largest SVRS manufacturers, wants to
explore the possibility further. The group recently collaborated on
a study that resulted in the 1.86-second time estimate.
“A vacuum release or vacuum limiting system, depending upon
pump-to-sump distance, may relieve the dangerous suction force
before full disembowelment occurs,” says Paul Pennington, PSC
founder and chairman. “This could be the difference between
life and death for the victim.”
When it comes to limb entrapment and whether secondary devices can
prevent it, experts generally agree that some limb entrapments can
be alleviated, but APSP officials take a more cautious
The association contends that it’s possible for swelling to
cause the limb to become stuck so tightly that it remains wedged
inside the pipe even after the suction is interrupted. Even if
significant swelling doesn’t occur, the skin may not respond
to efforts to pull the limb out: Just as it can be more difficult
to remove a ring than to put it on, it can prove impossible to pull
a limb out of a pipe, no matter how readily it slid in, APSP
For its part, PSC believes safety release devices are highly
effective in combating limb entrapment, and officials say most of
the known entrapped limbs were released after the suction was
Those against requiring an SVRS say that because they cannot stop
or even mitigate all types of entrapment, they should rarely be
“The fact that some percentage of [entrapments] could be
helped, some could be mitigated and others
there’s nothing that can be done [isn’t enough],”
Barnes says. “We draw the line on the side of safety that
says, ‘We’re not going to pick and choose. We’re
going to prevent all suction entrapments.’”
At the end of the day, there is one thing both sides agree on: More
research is needed.