The Case Of The Unheard Smoke Detector

A recently married upscale professional couple seemed to enjoy their comfortable life. They owned a modern two-story home valued in excess of $300,000. They had an old English sheep dog, kept in an attached garage with a "run" during the day. Inside the home, the couple kept exotic tropical fish in an oversized 100-gal tank, which sat on a custom metal stand also serving as a room divider.The couple

A recently married upscale professional couple seemed to enjoy their comfortable life. They owned a modern two-story home valued in excess of $300,000. They had an old English sheep dog, kept in an attached garage with a "run" during the day. Inside the home, the couple kept exotic tropical fish in an oversized 100-gal tank, which sat on a custom metal stand also serving as a room divider.

The couple had no children or a live-in housekeeper. They both took a commuter train to work every morning. As such, the house was empty until they returned in the early evening. This routine worked out quite well for the couple, until one day when they learned how something as common as an extension cord can change things.

On that day, a fire occurred in the house. There was minimal fire damage; however much of the contents suffered extensive smoke penetration. The couple's insurance company contacted our firm to investigate what occurred and, if possible, determine the responsible party.

In the course of our investigation but before our on-site inspection of the home, we learned the couple had moved the large, heavy, fish tank two months previously to accommodate new wall-to-wall carpeting. After relocating the fish tank, the owners realized it was too far from an electrical outlet to run the tank's air pumps, heaters, and lights using their respective electrical cords. To overcome the problem, the husband installed an extension cord under the rug, and connected its outlet to the fish tank's total electrical load (pumps, heaters, and lights).

After repositioning the fish tank, a portion of its metal stand rested on the extension cord, pinching its insulation. The couple also had numerous "throw" pillows used for TV watching. They were stored on the metal stand's lower shelf, in direct proximity to the extension cord.

An analysis of the problem We determined a small fire started because the extension cord overheated due to arcing between the conductors of the extension cord. The cord's heated insulation, where the fish tank's heavy stand rested on the extension cord, was distorted and weakened. There was evidence this was where arcing occurred; it started the fire in the insulation and rug.

In turn, the small fire started a smoldering fire in the pillows stored just above this area. As the pillows ignited, the flames heated the glass sides of the fish tank. The heat caused the glass to break, and a cascade of water flowed onto the fire. Although the blaze extinguished, the affected area continued to smolder.

The smoldering fire created a blanket of soot and smoke that permeated every nook and cranny of the home. The soot even penetrated closed cupboards, drawers, and closets. Although the fire was small (the large amount of water put out the blaze as efficiently as would have been done by a sprinkler system), the damage still exceeded $75,000.

As part of our investigation, we inspected each device serving the fish tank and found no problems with the air pumps, heaters, or lights. Upon inspecting the extension cord, we photographed the physical evidence. A large portion of the cord's two conductors appeared beaded together. We also inspected the overcurrent protection panel box and looked at the involved 15A circuit breaker, which was tripped in the off position. This breaker's circuit included the extension cord that powered the fish tank's electrical devices.

Under some circumstances, an arc between two conductors will produce a "dead short," and the breaker will immediately trip to the OFF position. But there are other circumstances that will allow the extension cord to overheat. An initial fire commenced before the breaker opened. During this time, the conductors in the extension cord could have approached a temperature of 2000 degrees F and would have become incandescent. As they melt, these conductors may separate and not trip the breaker. In this case, the conductors beaded together, and the breaker tripped.

The couple was both fortunate and unfortunate. The proximity of the "throw" pillows to the heated cord and the burning rug caused them to ignite. They were unfortunate in that if they had placed the pillows elsewhere, there would have been a limited fire and very little smoke damage. But, they were fortunate because the flaming pillows caused the fish tank's glass to break, which ultimately put the fire out. If not for the release of the large amount of water, the house might have completely burned to the ground.

To ensure a thorough inspection, we completed a diagnosis of exclusion. Given the fire damage was minimal, our investigation proved easier. We checked all electrical systems. The sheep dog was out of the main house and unhurt; he did not cause the fire. The exotic fish were a casualty of the fire, not the cause.

Benefits of exceeding code requirements What lessons can we learn from this case? * Electrical engineers, designers, and architects given design responsibility for electrical systems should pay strict attention to detail. You may place a fish tank and other items having electrical loads in an out-of-the-way location. Given that the NEC is a minimum electrical standard, upscale property may require additional outlets to eliminate the need for extension cords. * Electrical contractors should educate their customers on the dangers of extension cords. * Electrical inspectors should increase their vigilance when conducting inspections. * Not every fire causes a loss of life. But, even a small fire can cause extensive disruption and expense.

Forensic engineering is a tool that, when correctly used, will often lead to the accurate determination of cause. For this investigation, the insurance carrier would have preferred the cause of the electrical fire was defective equipment: an air pump, tank heater, tank lamp, or circuit breaker, to enable it to recover its loss.

Of particular concern for all of us is the problem of having smoke detectors that function when the house is empty. In this house, the smoke detectors would have alerted the occupants-had they been home. The neighbors did not have a key, did not smell smoke, and thought it prudent "to mind their own business."

One approach to protecting empty housing When this writer built his home, he installed an outside strobe light and loud horn at the peak of the roof. These devices connect to the home's smoke detection system. He also conducts monthly tests but prior to doing so, he alerts the neighbors. This installation was not an expensive option; yet it provides some peace of mind during periods of travel.

Of course, another approach is to have the smoke detectors connected to an off-premises alarm company. If you work as hard as this young professional couple (who suffered a substantial lifestyle disruption), you should think about ways to help protect yourself and your clients. We, who are members of the electrical construction industry, must lead the way.

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