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© Dr. Ray Franco, PhD, PE
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Vicksburg, MS
601.529.7473
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Identification of Fire Damaged Smoke Alarms


Smoke Alarms Non-Combustible Components

When a fire attacks and consumes the plastic body and combustible materials of a smoke alarm, the non-combustible components can be used to identify it. The non-combustible metal components of a smoke alarm include the horn piezoelectric disc, the ionization chamber, the radioactive source, and other metal components. The shape and dimensions of the components can be compared to those in known exemplar smoke alarms. Often the manufacturer can be identified from the metal components. For example, BRK brand smoke alarms have a v-shaped notch in their piezoelectric disc. Newer BRK smoke alarms have a unique spring metal clip between the battery and printed circuit board.

Fire  Survived Metal Components of a_BRK Smoke Alarm.
Fire Survived Metal Components of a BRK Smoke Alarm.
Notch in BRK Piezoelectric Disc.
Notch in BRK Smoke Alarm Piezoelectric Disc.

Fire Damaged Smoke Alarm Printed Circuit Boards

Printed Circuit Boards (PCBs) in smoke alarms are made of fire-retardant material. The shape and dimensions of the unknown smoke alarm PCB can be compared to those of known smoke alarms. To confirm that the PCBs are the same, the copper traces on the PCBs should be compared. If the PCB is covered by melted plastic, then it should be x-rayed.

Component Side of Printed Cirucit Boards

Subject Smoke Alarm PC Board
Front of Fire Damaged Smoke Alarm Printed Circuit Board (PCB).
Subject Smoke Alarm PC Board
Front of Exemplar Smoke Alarm PCB with Ionization Chamber Removed.

 

Back of Printed Circuit Boards

In the case below (#17-044), Dr. Franco was not only able to determine the model number of the smoke alarm, he was able to closely determine its age from exemplars.

Subject Smoke Alarm PC Board
Back of Fire Damaged Smoke Alarm Printed Circuit Board (PCB).
Exemplar Smoke Alarm 83R PC Board
The Fire Damaged PCB matched one of Dr. Franco's Exemplars.

At a joint laboratory examination, the smoke alarm PCB was cleaned up so that the revision and lot numbers could be read. Dr. Franco purchased 8 exemplar smoke alarms from eBay. The revision and lot numbers only matched one of the exemplars. Dr. Franco was able to determine that the smoke alarm around 24 years old. It was still in use at the time of the fire.

Subject Smoke Alarm Revision and Lot Numbers
Revision and Lot Numbers on Subject Smoke Alarm Printed Circuit Board (PCB).
Smoke Alarm PCB Exemplar Revision and Lot Numbers
Only one of the Exemplars matched the PCB Revision and Lot Numbers on the Subject Smoke Alarm.

Determing the Age from the UL Issue Number

In the case below (#16-055), the manufacturer and model number was obtained from the back of the smoke alarm, but it was too badly damaged to determine the date it was manufactured. Eight exemplars were purchased from eBay. Dr. Franco used the UL issue number to narrow the date down to 2 years. This fire was in August 2016, and BRK stopped manufacturering this model in September 2004. Hence, it was over 10 years old and out of date.

Heat Damaged Smoke Alarm and Junction Box
Heat Damaged Smoke Alarm and Junction Box.
Back of Fire Damaged BRK 4120 Smoke Alarm
On the back of the Smoke Alarm, the Manufacturer and Model Number, 4120, could still be read.
Smoke Alarm PCB Exemplar Revision and Lot Numbers
The UL Issue Number was just barely readable.
Smoke Alarm Exemplar UL Issue Number
The UL Issue Number of one of the Exemplars closely matched the UL Issue Number of the subject Smoke Alarm.

 

The bodies of smoke alarms are plastic that can melt and re-solidify. It is not unusual to have to x-ray smoke alarms to identify them.