Unintended water release in a residence is a frequent cause of damage (and insurance claims). Often, the water released is caused by a worn-out washing machine hose that ruptures, or an ice-maker supply tube that flexed one too many times and sprang a leak. These failures can result from a hose or tube defect, but often, they are caused by homeowner neglect or failure to replace an aged part.

When water damage begins suddenly in the attic space of a home, it may be tempting to blame it on a leaky roof. But if the weather has been clear for several days prior to the incident, an engineering investigation is in order.

Exactly this type of loss occurred in a 23-year-old Southern California townhouse.  The homeowners awoke in the middle of the night when they heard running water and found their bedroom floor covered with about an inch of water.  When the fire department responded to the homeowners’ emergency call, they found an air handling unit (AHU) in the attic was the source of the water streaming down the walls into the living space below. According to the homeowners, the air handler had been repaired in December, just two months before the incident, because it had not been providing any heat on cold nights during the early days of the winter season.

During our inspection, we discovered that the AHU contained 3 sets of coils: Two sets of coils in an older unit (blue and violet arrows in right photo below), and one additional coil that appeared brand new, but contained several cracked u-bends in the copper tubing (green arrows in left photo, coil removed in right photo). The first coil (blue arrow) was corroded and disconnected, and we determined that this was the hot water coil that had been in service until being replaced in December.  The second coil (violet arrow) was connected to refrigerant tubing that ran outside to a compressor/condenser unit. And the third coil (green double arrow in left photo indicating cracked tubing) was located downstream of the other two.

The cracks were obviously the source of the water leak, and we hypothesized that they were caused by freezing of the water inside the tubes, but the sequence of events wasn’t obvious until we examined the weather history from December to February. That winter, the weather was generally mild, but there was (a) a cold spell in December, about the time the AHU was repaired; (b) a spell of unusually warm temperatures in January, when air conditioning was needed in the townhouse; and (c) another cold spell right when the water release occurred, a time when heating was needed again.

It was obvious that when the HVAC technician installed the new heating coil, he violated a well-known mechanical code requirement – never install a water coil downstream of a refrigerant coil because the chilled air is cold enough to freeze the water, which causes ice expansion that leads to bursting of tubing and piping. Clearly this aspect of the installation was defective, but additionally, there was yet another defect that contributed to the damage.  He also failed to install a pan and drain underneath the new heating coil. When the homeowners called for heat during the February cold spell, and water began flowing out of the tubes that were ruptured during the January warm spell, it ran directly downward to the plywood flooring in the attic, rather than being directed outside via a drip pan and drain pipe.

The purpose of “Investigation Anecdotes” is to inform our readers about the intriguing field of engineering investigations. We hope you are instructed by this content, and we encourage you to contact us if you seek additional information. Copyright Martin Thermal Engineering, Inc. (2013)

A fire that originated inside a restaurant in a strip mall became the subject of litigation almost three years after the date of the fire. An adjacent tenant in the mall was pursuing a claim against the restaurant owner seeking recovery for his losses.

Subsequent to the fire, but before we were retained by the adjacent tenant’s law firm, the property had been rebuilt. Consequently, it was impossible for us to perform a site inspection, but we were able to review photographs taken by the responding fire department’s arson investigator.

Every investigator will acknowledge that his level of confidence in his own conclusions is usually higher when he has had the opportunity to actually examine the site and the physical evidence. Nonetheless, good investigators can often develop strong conclusions from photographic evidence alone, as long as other available evidence (e.g., eyewitness testimony, building records, fire personnel observations) corroborates the findings.

One technique that can be especially helpful for analyzing historical photos is photogrammetry. In the subject case, we wanted to determine if an oven’s exhaust duct was properly installed (i.e., did it have sufficient clearance between the duct’s hot walls and the building’s wood beams and joists). We used photogrammetry to assess the dimensions of both items.

Photogrammetry is the art and science of determining geometric properties of objects from photographic images. The two images on this anecdote page give examples of a photogrammetric analysis conducted as part of our strip mall fire investigation. In both images, the superimposed green lines represented known dimensions and the superimposed red lines represented unknown dimensions. By computing the relative lengths of the red and green lines, a multiplier was obtained and the unknown dimensions were determined from the known dimensions.

In the first photo above, the known dimension (green line) was a 4-inch electrical junction box, and the unknown dimension (red line) was the width of the square exhaust duct (determined by the analysis to be 24 inches).

In the second photo, the known dimension (green) was a 16-inch cement block, and the unknown dimension (red) was the distance between joist hangers (also determined to be 24 inches).

The photogrammetric results were ultimately compared to eyewitness statements and burn patterns to form a sound conclusion about the origin and cause of the fire.

The purpose of “Investigation Anecdotes” is to inform our readers about the intriguing field of engineering investigations. We hope you are instructed by this content, and we encourage you to contact us if you seek additional information. Copyright Martin Thermal Engineering, Inc. (2013)