When you know how to design a plumbing system, it’s difficult not to point out the impossible in movies.
It’s Oscar season, and by the time this is printed there will be a new Best Picture along with some speeches from the winners that may or may not have been booted off the stage by the Academy Orchestra. Movies can be an amazing reprieve from our day-to-day lives, a simple distraction from the RFI’s and the print date around the corner. As engineers you are cursed with the ability to question and challenge things that you see. Every so often my wife and I will be watching a movie, and I say to her, “Well that would never happen.” This is usually followed by a mixed grin and scowl. I’ll share with you one of the biggest engineering mistakes in one of the most watched movies of all time.
Spoiler Alert — The article below will give away the ending to the described movie.
One of my favorite movies is “The Shawshank Redemption.” The setting takes place in the Shawshank State Penitentiary where inmate, Andy Dufresne, uses his patience and brains to escape through the wall and plumbing system. He cores through the roughly 8-inch-thick wall with a rock hammer and uses a rock to break a hole in the cast iron sanitary waste line. Dufresne then proceeds to crawl through the sanitary waste line and eventually out of the compound where the pipe daylights to grade.
I’m sure I’m not the only plumbing engineer who is frustrated by this. Dufresne, played by Tim Robbins, probably has at least a 32- to 34-inch waist. I’m even counting for some weight loss due to the quality of prison meals. Based on this dimension and space needed to actually move, I have to assume that the pipe is 36 inches. That is one massive pipe serving the compound. Keep in mind I’m trying to justify this because I don’t want my favorite movie to have impractical plumbing systems. We have to assume it has some sort of combined sanitary and storm system. There’s no way the sanitary system on this facility could be 36 inches. My calculations are a function of the following research.
The movie was filmed at the Mansfield Reformatory because the prison has an architecture theme that’s daunting and cold. Based on the research, the reformatory contains 600 cells. Dufresne’s friend, Red, describes the cells in the movie as having a cold metal toilet with no seat or sink. Online pictures of the prison show that there are individual lavs in the cells, but let’s assume that Red was accurate in his description, and they added the lavs later per code. With the gang showers, laundry, cafeteria and some other guard latrines, I estimate that the facility had the following DFU loads:
So based on those calculations you would need a 12-inch cast iron pipe at 1/8-inch slope.
With that information I am assuming that Mansfield had a combined sanitary and storm system.
The IPC allows you to convert the DFUs calculated early into roof square footage for the combined storm system. 440 DFUs requires an additional 4,000 square feet for the first 256 DFUs and then 15.6 square feet for the remainder of the DFUs. Which looks like this:
X = (4,000 + ((4,440-256)*15.6))
The equation only works if you have at least 256 DFUs. This calculates out to add an additional 69,270 square feet of roof area.
Now that I have that information, I will need to calculate the building storm load. The architectural details of this facility are quite amazing ,seeing how the masons integrated the gutter and drainage system into the building. By using Google Maps, I was able to estimate the roof area to be approximately 85,000 square feet.
I started doing more research and found out that after filming several facilities on site were torn down making the Google Maps approach quite useless. The north and south ends of the building continued further and there were several out buildings. Based on the pictures and the 85,000 square feet, I am estimating another 50,000 square feet totaling 135,000 square feet. Now as you know for this calculation we’re going to need rainfall rates. I’m torn here because the building under question is located in Mansfield, Ohio, but the movie took place in Portland, Maine. So I’ll take the more conservative route and hope it doesn’t backfire. With Mansfield receiving around 2.7 inches per hour and Portland, Maine around 2.4 inches per hour for a 100-year storm, I will use Mansfield for the storm calculations.
With the sanitary waste calculations this gives a grand total of 220,000 square feet. This size is unfortunate because there is no table that has an area of this magnitude listed, so I need to convert this to GPM; 2.7 inches per hour is equivalent to 0.0281 GPM/SF.
220,000 square feet* 0.0281 = 6,182 GPM.
Using Manning’s Formula with the following assumptions I calculate that the required pipe size is 1/2 full, 2 to 5 feet per sec velocity, cast iron roughness coefficient of 12 and 1/8-inch per foot slope. The pipe needed for a combined storm and sewer would have to be 18 - 20 inches, depending on the manufacturer. Based on this information I can confidently say that Andy Dufresne would not have been able to squeeze into that pipe. The only other explanation is that the reformatory’s first project on the grounds was to install a new sewer system, and that this system is picking up other nearby storm connections and municipal sanitary loads. Just recently we had a prison break in New York where two men sawed their way into a 24-inch steam pipe that was turned off. Pretty smart. Those two men were way smaller than Dufresne, so I still have my doubts about the feasibility of his escape.
They also were eventually caught.
There are plenty other movie faux pas that have bothered me, as well as other engineers that I’ve talked to about this. In the movies, whenever anybody tries to utilize the ductwork in a building as a getaway route the duct above the ceiling just so happens to be a 72-inch x 72-inch duct. The ducts are so perfectly sized that the person and all of their friends can have a conference in them. Nowhere along their trip do they run into a damper or VAV box. Always over-sized ductwork! The last one is that the fire sprinkler heads in Hollywood are all somehow interconnected to activate when one sprinkler head is set off. Hollywood’s not fooling us.
I don’t know, maybe Dufresne was lucky enough to have the town sanitary main routing behind his cell. To quote him in a letter to his friend Red: “Remember Red, hope is a good thing, maybe the best of things, and no good thing ever dies.” Maybe that means that we as engineers should try to turn it off and focus on the good things like awesome movies, even if they do stretch our engineering principals a little.
Cory Powers, CPD, is an associate at HGA Architects and Engineers office in Milwaukee, Wisconsin. HGA is a top-10 national health care design firm with additional practices in energy and infrastructure, corporate, arts and higher education. Powers has a B.S. in Architectural Engineering from the Milwaukee School of Engineering. He is a licensed master plumber and certified in plumbing design (CPD). He has been a member of the American Society of Plumbing Engineers (ASPE) since 2008, previously serving as president of the ASPE Wisconsin Chapter. Cory currently serves on the ASPE National Board of Directors as the AYP chair. He can be reached at firstname.lastname@example.org