Super Trap

by Katie Lee

The importance of trap seal primers in health care and commercial buildings.

By Kevin Wong

We are living in an era of super bugs. Fifteen years ago it was SARS — tomorrow…who knows? The SARS bug literally shut down Toronto when the World Health Organization (WHO) made its declaration for the only North American city to come under the challenges of that bug.

The cost was in the hundreds of millions of dollars to the economy to come to grips with the epidemic at the time. The hotel, healthcare and restaurant industries in Toronto were devastated overnight.

As a young engineering consulting professional in the industry back then, our existing clients came to us looking for contingency plans, coping and quarantine strategies, and such. It was not easy; existing quarantine protocols and strategies could not cope with the additional stresses this persistent bug exerted on the existing knowledge base back then.

Hardest hit were the local hospitals and health care facilities. You sanitized the bug out of one floor or ward and it popped up a few days later somewhere else in the building. These were apparently separated and firewalled floors and wards. How was this happening? That fear translated itself to other occupancies, including restaurants.

Slide1No one would have predicted that SARS was strong enough to survive and travel through the dried trap seals between floors. That was what we learned.

That was 15 years of hard experience, deaths, and millions of dollars studying the challenge. As it turned out, dried traps in the quiet, unobserved portions of the hospital facility allowed the bug to spread. It was an odd culprit. These unassuming spaces are often considered the least risky and cleanest spaces; disinfectants and chemicals are stored there in a dry, climate-controlled environment. But they are in an ignored space, which creates an opportunity for a dry trap seal. Low humidity in unused spaces leaves an opportunity for sewer gas to travel not just out of the sewer into the building but also for fumes, gases and vapors laden with pathogens to travel between floors and zones within the building. Tough learning a decade and a half later.

Why is this important today? Simple answer: If not SARS, the next superbug is always on the horizon. We can’t predict when and where it will strike, but we know it is coming. Building systems design has to change. Thankfully, those who write the codes — as well as those who design and build buildings — recognized this. There are many emerging concerns to cater to though.

The environment is changing; our demographics are changing; our existing infrastructure is aging. With our aging population, the current concern is legionella. The 2020 Canadian National Plumbing Code aims to add language to the codes to address this growing concern. While this means looking at ASHRAE Guide 12 and the new ASHRAE P188 standards, the simplest thing to add to a building design to ensure that management of pathogens is a maintained trap seal to keep vapors out of the occupied spaces.

For the uninitiated, the trap seal is the water level in the p-trap that ensures that sewer gases do not come out of the floor drain, sink or bathtub. Water does a great job of keeping gases from migrating into the building’s occupied spaces.

Historically, this meant the prevention of often explosive sewer gases from concentrating in the home or building where it could, theoretically, cause the space to blow up. We have had stunning occurrences in our plumbing history. Closer to home, it keeps the stinky sewer gases from smelling up the little used basement bathroom or the even less visited utility room.

In the healthcare setting, this means something more — not just the smell or the risk of explosive gases gathering up to cause danger. A healthcare facility is also where we find some of the most concerning pathogens in abundance. Wards and zones are created within these buildings to ensure the management of the spread of these little guys. What we learned from the SARS outbreak in Toronto, the trap seal now plays an even more important role is infection control.

The simple solution is to design trap seal primers, which automatically maintain these trap seals, into the building. There are technologies around to do this.

Building designers use these strategies on often-used points like sinks where everyday use maintains the water in the traps. In less used spaces, electronically programmed or automatic trap seal primers are necessary because you can’t depend on the building users to maintain the seals. Here again the engineer must design in an automatic trap seal primer to manage these traps. These have to be designed simply because plumbing and drainage is often invisible to the building users until something goes wrong.

To manage the risk of more than just gases entering a building, an emerging trend is the use of manual trap seals, caps and items that allow water to go down but restrict gas and even insects from coming up. Codes are being changed today to make these new risks manageable.  

Trap seals, through their simplicity and rigor of design, offer an elegant solution to managing traditional and emerging threats to our buildings and health today in an important and often invisible part of the building’s mechanical system.



Severe Acute Respiratory Syndrome and the humble P-trap

Pathogen cross-transmission via building sanitary plumbing systems in a full scale pilot test-rig

Defective Trap Seal Identification System

The fight against SARS: A backfilling connection for the prevention of drying out of floor drains’ U-traps

Report details lessons from SARS outbreak


— Kevin Wong is the Canadian national specifications manager with MIFAB, a manufacturer of specification drainage products, access doors, steel, plastic, concrete and stainless steel trench drains, trap seal primers and water hammer arrestors, HDPE grease, oil and solids interceptors, no hub couplings, BEECO backflow preventers, pressure reducing valves, strainers and gate valves, dialysis boxes and HydroMax siphonic roof drains.

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