I blogged on the extent to which an expert’s investigation of cause relies on Observation compared to laboratory and field testing. (Ref. 1) An example like the following will help understand this – a surprise observation at the end made it an enlightening investigation too. The observations are italicized in the following.

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I was retained to determine the cause of water on the floor of a finished basement of a commercial building in Halifax. It was only a mini-flood but dangerous because the water was running down a basement wall, at the location of the electric supply to the building, and into an electric room.

The mini-flood, water problem

I was told by the owners and subsequently saw that the water appeared on the floor of the electric room, and a conference room beyond, a couple of hours after a rain storm started. I also saw that the mini-flooding occurred during a rain storm blowing hard out of the southeast over a long, exposed fetch.

I did the usual starting with the big picture by learning how the building was constructed including all sources of water on the roof and how these were drained.

I then removed the gyproc wall in the electric room to expose the top of the concrete basement wall and a circular plug of concrete near the top. I saw that the power supply cable was enclosed in the plug of concrete. I also saw on a wet day water seeping from the bottom of the plug down the concrete basement wall to the floor of the electric room. As the rain storm continued the wetness at the bottom of plug crept up the plug and the flow of water to the floor increased.

Power supply design and construction

I checked on the outside of the building and saw that the power supply cable to the building was enclosed in a 4″ diameter PVC pipe down the outside of the building then horizontally into the electric room. The electric cable from the street entered the top of the PVC pipe beneath a canopy after curving down then back up to form a drip-loop. The horizontal pipe was enclosed in a plug of concrete where it passed through the basement wall near the top. This was the same construction seen behind the gyproc wall inside the building.

This was a typical power supply construction for a building. You see it often, even on houses. Cable sizes, PVC pipe size and length of drip-loops vary but the basic design is the same.

I spoke with the electrical engineers who designed this installation and learned it was constructed in 2004. There was nothing unusual about the design.

I also visited and spoke with the company that sells this type of PVC pipe for electric services. There was nothing unusual about the pipe; longer lengths for the side of a building and shorter pieces for the horizontal section into the electrical room. An elbow-shaped piece connects the vertical PVC to the horizontal. The shorter horizontal piece had a cap bolted on at the elbow. It provided access to the inside of the section of the PVC pipe where the cable changed from vertical to horizontal and into the building.

Chasing down the water’s path

I removed the cap at one point and saw the cable in the pipe. I was surprised to see sediment on the invert of the elbow and staining a couple of inches up the sides of the pipe. There were also small holes in the invert of the horizontal section of pipe plugged with the sediment – these holes did not appear in the pipe that I saw at the PVC pipe vendor.

The space between the cable and the inside of the PVC pipe was tightly caulked at one time but movement of the cable as it expanded and contracted with the air temperature opened up space between the cable and the caulking over time. I can imagine heat from the electric cable contributed.

Conclusion

So, I concluded, rain water was getting into the vertical PVC pipe, then down the pipe and along the horizontal section to the inside of the building. This was expected during design of the electric service as evident from the drain holes in the invert and the caulking around the cable. This was the water I saw when we removed the gyproc wall inside the electric room. The water would have drained away to the outside of the building at one time but the holes in the invert were now plugged with sediment.

Conclusion

So, how did the rain water get past the drip-loops? I thought about this and concluded up-gusts of the rain-soaked wind were the culprit. We occasionally see these up-gusts in rain and snow storms. And, like said above, water was appearing on the electric room floor during hard blows out of the southeast, a wet point of the compass Down East.

I had my well substantiated cause – based on observations – and reported to my client as found above. There were a number of observations during my investigation and mini-conclusions along the way but I was confidant and went on my way after submitting my report.

Note: The foregoing forensic investigation was based on observation alone – no laboratory or field testing to be seen anywhere.

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A surprise, irrefutable, clinching observation

Months later in April I ended up in hospital for a common mini-medical problem. I was on the fourth floor looking out the window at the roof of an adjacent two story building with a number of chimneys and vent pipes. And there were the up-gusts in the wind around each pipe. They were evident because moisture in the warm air was condensing in the cool April air on discharge from the pipes. The same kind of up-gusts I hypothesized about months earlier at the mini-flood building.

References

1. One forensic observation does not a cause make. Posted July 18, 2023

(Posted by Eric E. Jorden, M.Sc., P.Eng. Consulting Professional Engineer, Forensic Engineer, Geotechnology Ltd., Halifax, Nova Scotia, Canada, July 31, 2023. ejorden@eastlink.ca)   

The word empirical keeps coming back to me after posting a recent blog about the importance of peer review in forensic work. (Refs 1, 2 and 3) This because many forensic engineering investigations of failures and accidents in the built and natural environments are empirical in nature. Meaning, they are based on observation or experience not laboratory and field testing.

The Observational Method – or Empirical Method, if you like – is widely used and accepted in both the theoretical and applied sciences. Check out Dr. Google:

• Civil, geotechnical and environmental engineering. The OM method is particularly valuable in geotech work because the engineering properties of the ground can change with every step.
• Design and construction
• Forensic investigation
• Criminal investigation
• Psychology
• Child development
• Anthropology
• Marketing
• Statistics

What needs to be understood is that, in general, one forensic observation is insufficient in determining cause. Cross checking is essential. Several observations must be made and a number of these – the preponderance – must point to the probable cause of a failure or accident. If this is not done, peer review will flush out the fault.

In general, the Observation Method, regardless the field of practice, like in the above list, involves:

• Preparing a preliminary design or investigation based on what is known at the time. This could be of an engineering structure or the forensic investigation of the failure of one, a research study, treatment of a PTSD patient, etc. – anything where there are unknowns.
• Preparing a monitoring plan to verify, for example, that the forensic investigation or research study is yielding expected data or findings.
• Preparing a contingency plan that is put into operation if the data or findings are not within defined limits. For example, if the preliminary design is of an engineering structure, and different foundation soil conditions are found during excavation, a contingency plan might require deep piled foundations rather than shallow ones. Or, the initial findings of a forensic investigation are incompatible with the initial hypothesis of the cause of a failure or accident, then the hypothesis is modified and additional investigation is done.

Getting back to empirical, I don’t remember the last time that I did a forensic investigation that was based on laboratory testing. Field testing, yes, plus lots of observation and experience. Testing like the re-enacting of accidents, testing the layout of a highway design, or field testing the properties of materials used in construction. There’s one field test I do – 10 times in each of three (3) different directions.

Why is talk about observation and experience, and peer review, important? Because forensic engineering investigations based on the Observation Method – many are – are best served when a peer review is carried out on completion of the investigation. Better a peer review than a rebuttal review if dispute resolution or insurance claims adjustment is not reached on the court house steps.

References

1. How are forest fires and earthquakes similar, and what can experts learn from them about the importance of peer review? Posted June 27, 2023
2. Update: A Bundle of Blogs: On the need for peer review in forensic engineering and expert services. Posted April 28, 2021
3. A Bundle of Blogs: On the need for peer review in forensic engineering and expert services. Posted November 29, 2019 There are seven (7) good reads on peer review in this blog including the two (2) in the Update

(Posted by Eric E. Jorden, M.Sc., P.Eng. Consulting Professional Engineer, Forensic Engineer, Geotechnology Ltd., Halifax, Nova Scotia, Canada, July 18, 2023. ejorden@eastlink.ca)