Are Pool Drains Dangerous?
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Are pool drains dangerous? If you are here looking for answers about the drain in the bottom of your pool and whether there is any concern or risk of danger from these underwater suction outlets then you need to be aware that, yes, pool drains can be dangerous. I mean they are not supposed to be dangerous, and in fact there are laws and construction standards in place to make them not be dangerous, but as a swimmer in the pool there is no way to be certain whether this particular drain is dangerous or not. Perhaps you can take this as the point of the article in short form - swimming pool drains can potentially be dangerous and so as a general precaution you should always treat them as potentially dangerous.
Let's start from the beginning with pool drains and talk about what they are and the function they serve. First, the name for the suction outlets on the bottom of the deep end of your pool are "main drains". Despite how the name sounds it is important to recognize that these are not actually drains at all, but instead are suction ports that are part of the closed loop plumbing system for your pool filtration. Main drains are somewhat of a misnomer as they do not drain the pool at all, any more than calling your skimmer a "skimmer drain" which again would not be aptly named. Instead of calling it a main drain which can confuse some people you would better off to refer to them based on their function, which is submerged suction outlets. Confusing matters further there are actually quite a few different potential configurations for main drains which affects how they function (as well as their potential for being dangerous to swimmers).
Active main drains - Active main drains are where there is direct suction from the pump through the main drains of the pool. In this situation water is drawn both from the main drains as well as the skimmers and into the pump. The suction created by the pump is very powerful and this creates what is known as an "entrapment hazard" underwater. There are a number of protections in place to prevent or at least minimize the potential for entrapment hazards from active main drain systems however death and accidental drowning from underwater suction drains is not uncommon. The amount of suction force which can be generated by even a modestly sized pool pump is far greater than the force a human can generate to attempt to remove themself from an underwater suction port. This is why pools must be built and maintained in such a way as to minimize this potential risk.
Passive main drains - Unlike an active main drain system a passive main drain installation does not actually receive direct suction from the pump. With a passive main drain system the pipes connected to the main drain do not connect to the pump on the other end, but instead connect with a non-pressurized equalizer line to the underside of the pool skimmer. In this installation the main drain allows water to equalize with the pool skimmer such that if the water level in the pool were to fall below the mouth of the skimmer the pump will not run dry. The equalizer line will allow water to fill into the skimmer body even when the water level in the pool is below the mouth of the skimmer. This protects the pump from damage (from running dry) and allows the pool to continue to operate and filter water even when the water level is lower than it is supposed to be.
In theory a passive main drain is safe from suction entrapment since there is no direct suction reaching the main drains. Only if a suction plate is added to the skimmer would it be possible for the main drain lines to become active. This skimmer suction plate is a relatively uncommon addition to the skimmer. It does not need to be there for the pool to operate under normal conditions, but when used effectively makes the suction from the pump transfer from one bottom port on the skimmer to the other bottom port. So in this way you can end up with an active main drain where it used to be only passive. Confused yet?
The problem is there are a lot of ways to build a pool, some pools are new, some were installed 50 years ago, not to mention regional differences in how pools are constructed. It is hard to give a clear accounting of the potential for danger with main drains because there are so many different ways to install one, or use one, or modify a system that it would be difficult to simply say that main drains are safe. There is always a concern that the pool is not built to code or has been altered or not maintained to current safety standards. As a swimmer you must choose to err an the side of caution as it will not be definitely clear one way or another whether your pool drains pose a potential for entrapment or not. Consider a few of these red flags that might indicate the potential for danger with your main drains:
Broken, cracked or missing main drain covers - If the main drain(s) in your pool have broken, cracked or missing suction grate covers this is a black and white safety violation. Main drain covers must remain on the main drain at all times, and any deficiency such as cracking, missing screws, or covers missing altogether are enough of a safety violation that the pool should be closed to all swimmers until the problem can be rectified. This is true for both residential pools as well as commercial pools. Residential pools can actually be worse in this regard as there are inspectors for commercial pools who will certainly close the pool for missing / broken main drain covers. In most cases there is no oversight for residential pools and as a result the onus of responsibility falls on the pool owner to make repairs when they are required. Even if the main drain is completely passive with no direct suction a properly fitted (and VGBA compliant) main drain cover must be in place. Pump suction is not the only element of danger for a pool drain though it is probably the most significant danger. Having an uncovered main drain (even without active suction) poses specific risk for mechanical entrapment with swimmers. Getting stuck on the bottom of a pool for any reason is a life or death situation where there is literally seconds to react before disaster.
Old main drain covers not meeting VGBA standards - Pools built prior to 2007 will all need to have the main drain suction grates upgraded to new VGBA anti-entrapment compliant covers. These new main drain covers are designed to be unblockable as well as having posted maximum flow rates embossed right onto the plastic of the cover. Commercial pools have more regular inspections for deficiencies like this however most residential pools will require the pool owner to be proactive in replacing old, outdated main drain covers.
Single main drains which are active - Any active main drain, which is to say a main drain that has active suction from the pump reaching the floor of the pool must be divided into dual suction ports, hydraulically balanced and a minimum spacing of three feet apart. While an SVRS pump can sometimes be used to lessen the risk of single suction main drains any swimmer in the pool should assume the drain to be active, and dangerous. Any time that a pool is renovated you should endeavor to upgrade all components of the pool to meet current safety standards, including splitting the main drain into a dual suction system.
Main drains exceeding maximum design flow rate - All main drains must operate within the flow limits as established by the manufacturer in order to meet VGBA anti-entrapment compliance. The flow rates should be embossed directly in the plastic of these main drain covers. If a pool system receives an upgrade like a new pump which is more powerful than the old pump, or if the original equipment was not sized correctly, then you can end up with a main drain with too much suction, which creates an entrapment hazard even if all other aspects of VGBA anti-entrapment guidelines are followed. This is one of the reasons why swimmers should assume main drains and any submerged suction outlets to be dangerous. It is not practical for the swimmer to be able to know if the system is operating within the limits of VGBA compliance for flow rating or not.
Custom built main drains not meeting size and depth standards - Some swimming pools like certain concrete pools will not use prefabricated main drain suction outlets, but instead use a custom built pit along with manufactured "frame and grate" covers. Custom built sump pits in pool main drains must also meet anti-entrapment hazards including minimum sump depth as related to flow and pipe size. Again it would be impractical for an average swimmer to know whether the main drain sump pits are designed to meet current anti-entrapment standards and so it is only prudent to assume there is a potential for danger and avoid playing with or around main drains.
Altered systems not meeting current codes for anti-entrapment are more common than they should be on residential pools due to the lack of oversight or enforcement of these standards. While a reasonable measure of safety is possible following accepted industry standards for installation the reality is that many pools even today are installed that do not meet these standards. Pool owners need to be vigilant with learning about pool safety and onus of liability / responsibility when it comes to things like VGBA anti-entrapment standards. While entrapment hazards are less common than they used to be in previous generations we are not at the point yet where you can just jump into any pool and make assumptions of safety. It is best to operate with a reasonable suspicion of danger when it comes to swimming around any submerged suction outlets in a swimming pool.
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