One of the drawbacks of fire investigation is that we rarely see the start of a fire unless it’s during training. Many small fires are not reported, which is a shame as it is these small fires that are the telltale of a major incident waiting to happen. Without investigation the subtle signs of what actually failed and consequent learning points might be lost.
Here’s a fire that was a near miss. This couple were alerted by the smell of burning, saw smoke pouring out of the front of the dishwasher and flames visible inside a hole that had opened in the plastic casing. They had the foresight to turn off the electricity before pouring a jug of water through the hole. The dishwasher was 7 years old and had no signs of failure or a problem prior to this. Also, the house was quite new and fitted with a modern breaker box with RCDs, yet none of the safety circuitry tripped.
The dishwasher is a Hotpoint DWF70S. You can see from Figure 1 that the front left casing of the door is breached. We opened the top section to reveal the circuit board that was mounted in this location. The board previously had two wires going to the lower edge that were now hanging off. The board has sustained significant heat damage which had melted the plastic mount behind it. A section of the board had been melted out in the shape of three sides of a square making quite a unique pattern.
A thick block of polystyrene was fitted into the front door panel and had started to melt/burn at the very top where the fire had started. Figures 2 and 3 show the internal damage viewed through the hole and with the casing removed. In Figure 3 the polystyrene block is visible. Figure 4 shows a closer look at the wiring on the board.
Had the fire taken off and burned out the kitchen or beyond, then reconstruction may well have found only that the fire came from the area of the dishwasher but nothing more specific. The fire would likely have breached various electrical wires causing the main breakers to trip, possibly raising the argument that the dishwasher could not have caused a fire without the electrical supply tripping before anything could have happened. It is seen that an electrical fire can evolve without tripping the electrical supply.
Examples like this from actual cases are useful training aids. This Printed Circuit Board fault is similar to the one that has affected Bosch, Neff and Siemens dishwashers that were recalled in July 2011. To date, Hotpoint have not issued a product recall for the same fault, that can totally destroy the dishwasher.
Dr David Schudel, BSc, D-ABC, CChem, MRSC, CFI