Getting stuck “between a rock and a hard place” is something that happens to most all of us as we navigate through life. It’s that sinking feeling you get in your gut when you must make a tough decision. Most of the time, we get stuck there because of an unforeseen condition so we shouldn’t be too hard on ourselves. Sometimes, we see it coming from a mile away — that’s what is referred to as a “train wreck.”

I’d say one of the more rewarding parts of engineering is helping people make their situations better. In recent years, I’ve seen a few projects that have had very large concrete grease interceptors. Back in the day when kitchens served full meals, the civil engineering methods for sizing interceptors prescribed large, concrete type interceptors. On one job, they had an existing 8,000 gallon concrete interceptor. It so happened that the interceptor, which was about 8 feet wide by 17 feet long by 12 feet deep, was in the way of the new building foundation. Based on the way that kitchens operate nowadays, we felt confident that we could specify an engineered grease interceptor that would be much smaller, serve their needs better and not affect the facility’s plans for a new building addition. Sounds like a “no-brainer,” right?

We got stuck between a rock and a hard place. As they went to install the new grease interceptor, which was right-sized from 8,000 gallons to 1,500 gallons, the construction team found a very large rock that was smack dab in the way of where everything was supposed to go! Despite everyone’s best intentions this was an unfortunate circumstance that gives you that sinking feeling in your gut and makes you wonder, “What could I have done differently?”

The interface between site utilities and plumbing engineering is something we should pay very close attention to. Any type of plumbing system that requires a buried tank, vault, pump station, interceptor, stormwater recharge, septic field or the like should warrant special attention. These are sometimes referred to as “dedicated systems” and some jurisdictions put more responsibility on the plumbing engineer to get it right. This means that we need to familiarize ourselves with utility drawings, topographical drawings and geotechnical reports. Plumbing engineers should be able to ask the right questions to our civil engineering counterparts.

I was fascinated to work on one building where the geotechnical engineer explained to me that I needed to pretend like the underslab soil was not even there. They had gotten into cahoots with the structural engineer and designed a building with deep structural concrete footings. The dirt underneath the building didn’t even play a factor in holding the building up, so I needed to make sure that my underslab piping was supported from the concrete floor structure like any of the stories above.

Rocks come in all shapes and sizes; even the little ones can put you in a tight corner. At some point in every plumbing engineer’s career, there will come a time when you may need to include a buried fiberglass tank. Buried tanks come in handy when designing many of the aforementioned dedicated systems. I worked on a school building once that was supplied with a 10 gpm well pump. To provide adequate capacity for domestic and fire protection, the design included a buried tank so there would be enough water in reserve. When crunch-time came to finalize the design, I was pushed out of my very narrow area of expertise and asked to detail the tank burial. There was a mistake on my detail that referenced the incorrect “coarse aggregate,” or stone size. Let me tell you, those 1/2-inch washed pebbles can cost a mighty penny.

Broadening horizons

I think it’s important that we look to broaden our horizons because it allows us to be more helpful to others. Sometimes, it’s important because, quite frankly, it’s our job and that’s what people pay us to do. A major consideration with the engineering of mechanical building systems is designing for seismic activity. This design consideration is relative to the biggest rocks of all, the crust of the Earth. When the crust of the Earth decides to move, everything above it also moves. Building codes require us to design systems to “resist total design forces.” Many times, this can include seismic restraint.

In the “ASPE Plumbing Engineering Design Handbook, Volume 1: Fundamentals of Plumbing Engineering,” Chapter 9 covers the Seismic Protection of Plumbing Equipment. The design handbook reminds us that the primary focus of designing for seismic activity is on the lateral or horizontal loads, since we already design piping to be supported based on weight. The key to designing for seismic activity is determining the Seismic Design Category of a structure. The SDC is based on factors such as “building importance,” location relative to seismic activity and something called “spectral response acceleration,” which can be explained by the motion of a slinky.

As an example, the language from one construction standard allows the following exceptions from seismic restraint for buildings in higher Seismic Design Categories:

“Exceptions: Seismic restraint may be omitted for the following installations:

A. Gas and medical piping less than one inch inside diameter;

B. Piping in boiler and mechanical equipment rooms less than 1 1/4 inch inside diameter;

C. All other piping less than 2 1/2 inch inside diameter except for automatic fire suppression systems;

D. All electrical conduits, less than 2 1/2 inch inside diameter;

E. All rectangular air handling ducts less than six square feet in cross sectional area;

F. All round air handling ducts less than 28 inches in diameter;

G. All ducts suspended by hangers 12 inches or less in length from the top of the duct to the bottom of the support for the hanger;

H. Equipment weighing less than 400 pounds, supported and attached directly on the floor; and

I. Equipment weighing less than 20 pounds suspended from the roof or floor or hung from the wall.”

Challenges come in all shapes and sizes. Sometimes, even the smallest challenges can have a large impact. If you ever get stuck between a rock and a hard place, sometimes the best thing you can do is just roll with it. In other words, “Rock and Roll!”

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