Don’t Get Blown Away: The Dangers of Pressurized Pool Filters

By: Lauren Broom

For pool service professionals, a pressure filter can look like just another piece of equipment on the equipment pad. But inside that tank is stored energy—and when something goes wrong, the result can be catastrophic.

A pressurized pool filter is essentially a pressure vessel containing water, and sometimes trapped air. If pressure is not properly relieved, or if a clamp, lid, valve, tank, or other component fails, the tank can suddenly separate and release that stored energy.

The consequences aren’t theoretical.

A well-documented article, “The Bomb in Your Backyard,” describes numerous pool-filter incidents involving severe traumatic brain injuries, blindness, facial fractures and deaths. The article notes that pressure-filter explosions have been documented for decades.

OSHA Has Investigated Serious Pool-Filter Injuries

OSHA’s own accident investigation database contains several cases involving employees working around pressurized pool filters.

In 2012, a Leslie’s Poolmart employee was servicing a residential pool when a filter housing lid flew upward and struck him in the head. He spent two weeks in the hospital and suffered facial fractures and short-term memory loss. OSHA reported that the filter’s T-bolt apparently pulled out of the clamp assembly because of excessive pressure.

In another OSHA investigation from 1994, a hotel maintenance supervisor was cleaning pool filter elements when the top section of the filter blew off. The employee suffered a concussion, skull fracture and facial lacerations. OSHA reported that the filter had apparently been improperly reassembled before the pump was turned on.

And one of the most sobering OSHA cases occurred in 1990. An employee had completed service on a large stainless-steel pool filter. A blocked valve prevented water from properly discharging, pressure continued to build, and the two-piece housing eventually separated. The upper housing struck the employee in the head, killing him.

These cases demonstrate an important point:

The danger isn’t just opening a filter. The danger is stored pressure and the possibility of an unexpected release.

It Isn’t Just Cartridge Filters

Pool professionals need to recognize this hazard across multiple types of pressure filtration equipment:

Pressure cartridge filters
The tank may be secured with a clamp, locking ring, or other mechanism. Improper assembly, damaged components, excessive pressure, trapped air or a failed fastening system can create a serious sudden-separation hazard.

Pressure DE filters
DE filters can have the same fundamental hazard. When the tank is pressurized, removing the lid or disturbing the closure before pressure has been completely relieved can result in a violent release.

Pressure sand filters
Large commercial and residential sand filters also contain pressurized water. Multiport valves, backwash valves, blocked plumbing, improperly positioned valves or other restrictions can create dangerous pressure conditions.

DE separation tanks
Don’t overlook separation tanks. OSHA investigated a 2011 incident in which an employee was cleaning a separation tank and its lines. Air pressure built up and forced approximately 200°F water out of the tank, causing severe burns that required hospitalization.

The hazard can therefore involve more than a lid flying off. Stored pressure can release water, air, chemicals, DE, or equipment components with tremendous force.

Read the Warning Sticker—It Is There for a Reason

Most pressure filters have a separate hazard/warning notice, often applied as a sticker directly to the side of the filter tank or near the lid.

Don’t ignore it.

That warning is not simply a manufacturer’s legal formality. It is communicating a real hazard to the person who will eventually have to service that equipment.

Before working on a pressure filter, the service professional should know:

• What the manufacturer’s instructions require.
• The filter’s maximum operating pressure.
• How the system is designed to relieve pressure.
• Where the air-relief valve is located.
• How the filter should be properly opened and reassembled.
• What condition the clamp, locking mechanism, lid and tank are in.
• Whether valves can trap pressure in the filter.
• Whether another person or automated control could restart the pump.

How Pool Service Pros Can Reduce the Hazard

The best approach is to eliminate the exposure whenever possible, rather than simply relying on PPE.

A good pressure-filter service procedure should include:

1. Shut the pump off and isolate the energy source.
Don’t assume that turning off a timer or control panel is enough. Follow your company’s energy-control procedures and make sure the pump cannot unexpectedly restart.

2. Relieve pressure before touching the filter closure.
Use the manufacturer’s specified air-relief and pressure-relief procedure. Never assume a gauge reading—or lack of a gauge reading—is enough by itself.

3. Verify zero pressure.
Don’t put your hands on a clamp or attempt to open a lid until you have confirmed that pressure has been relieved according to the manufacturer’s procedure.

4. Never defeat a safety device.
Don’t remove, bypass, plug or modify an air-relief valve or other pressure-safety component.

5. Inspect before reassembly.
Look for damaged clamps, locking rings, bolts, threads, tank components, lids, O-rings and other hardware. If something doesn’t look right, don’t put it back into service.

6. Never stand directly over the filter during startup.
If there is a failure, you don’t want your head and upper body positioned in the potential path of a lid or component.

7. Control the restart.
Make sure everyone understands when the system is being restarted and keep personnel out of the danger zone.

8. Follow the manufacturer’s instructions—not what you’ve always done.
Pool professionals often service hundreds of pools, and familiarity can create complacency. Different filters have different designs, pressure ratings and opening procedures.

Can We Design the Hazard Out?

This is where the industry should be thinking beyond simply telling technicians to “be careful.”

If a piece of equipment can be redesigned to reduce the opportunity for human error and make depressurization and access safer, that’s worth considering.

One example is the AquaStar Pipeline Filter. AquaStar describes its Pipeline Filter as a cartridge filter designed with a patented double-locking system intended to provide safe, quick depressurization and easier access compared with traditional clamp-style filters. The company currently offers the PLF27000 and PLF35000 models, both with a listed maximum working pressure of 50 psi.

Its manufacturer’s safety instructions still emphasize that high-pressure water and pressurized air can cause severe injury or death, and instruct users to disconnect pump power, properly depressurize the filter and never use compressed air to pressure-test it.

That’s an important distinction:

A different filter design doesn’t eliminate the pressure hazard. It can, however, be part of a strategy to reduce the opportunity for a dangerous human-error event.

Don’t Become the Next OSHA Case

Pool professionals work around pressurized equipment every single day. That familiarity can make a dangerous piece of equipment seem harmless.

It isn’t.

A filter lid can become a projectile. A blocked valve can turn a filter into a pressure problem. A damaged clamp can fail. Trapped air can increase the hazard. And a separation tank can release extremely hot water.

The goal shouldn’t be to teach technicians how to survive a filter failure.

The goal should be to prevent them from ever being exposed to the failure in the first place.

Before you service that filter, stop, isolate, depressurize, verify and inspect.

That warning sticker on the side of the tank is there for a reason.

Take it seriously.

Safety note: This article is educational and does not replace the specific manufacturer’s instructions, your company’s written safety procedures, or applicable OSHA requirements. Always follow the procedures and pressure limits for the specific equipment being serviced.

Sources: OSHA accident-investigation records and Plaintiff Magazine’s “The Bomb in Your Backyard.”