How Scary is an Electrical Fire?
An Electrical fire on board a boat can lead to some catastrophic outcomes if you do not control and manage the cause
I have seen two electrical fires on different boats in the past six months and in one case it was extinguished almost immediately, with damage being contained to the circuit causing the problem. It was dark and out in the ocean so it had its own terrors. In the second case it was far more extensive as it impacted a wiring loom, had the potential to expand to the boats structure, e.g. wood work, and took a lot of effort in a smoke filled environment to extinguish it, and it was daylight and not far off the marina.
So lets talk about fire. I am a trained CFA fire fighter, so I have had some of the specialist knowledge drummed into me both in the fields and classroom. Fire fighter training is based around what is known as the Fire triangle that is used to represent the three components of a fire: Heat, Fuel and Oxygen. For the various types of fire one can experience the complexity of the components of Heat, Fuel and Oxygen can vary immensely. However an electrical fire is relatively easy to manage. If you can eliminate the electricity generating the heat there is a very good chance that the fire will cease almost immediately. Other types of fire may require the removal of one of the other sides of the triangle, e.g. using a CO2 extinguisher to remove oxygen, or using water to cool the fire.
In the case of an electrical fire there is very little value in using a fire extinguisher if you cannot eliminate the heat generating electricity, it will continue to present a dangerous risk of fire. A fire extinguisher only really comes into play if secondary fires start in the structure (e.g. woodwork etc).
In the case of the second electrical fire I witnessed, on my own boat, there were a lot of contributing factors that caused the fire to continue burning even after the master switch had been turned off. For those of us that own older boats there are some simple things to go and have a look at that may mean you can stop the fire quickly and reduce the level of risk to yourself (e.g. smoke inhalation), and to your boat.
The root cause was a relatively large diameter wire that had been damaged some time prior to my taking possession of the boat, it was coloured black indicating it was a negative lead, but connected to a battery positive connection at one end and the starter motor at the other end. It had been taped up about 1/3 way along its length to insulate the damage.
I had been laying replacement wiring for a new alternator I was fitting. Pulling new wires through the boat appears to have disturbed the insulation tape repair site resulting exposing the damage. It somehow managed to come into contact with a point to earth the circuit, which in turn started to generate sufficient heat to melt insulation on wires cable tied to it.
All very simple, kill the power to the exposed cable and it all stops. Except this particular wire was directly connected to the battery for some reason and it was not until the bolt cutters were used to cut all wires on the batteries that the fire stopped.
What are the lessons to be learnt from this?
- Know your boat. I knew where to look, places to go to in order to maximise the effort to eliminate the problem, and what to use in a hurry. If I did not have bolt cutters readily accessible I may well have reached the point where we had 5 people in the water and a fully engulfed fire.
- There should be no un-fused or un-switched positive circuits connected up on the boat, particularly wires of a diameter that will carry large current for long enough to generate significant heat to start a fire. Ensure that the Alternator output lead, and Starter motor power lead are back to your battery selector switch and not direct to the battery (as was the case of the damaged starter motor cable that caused the problem).
- It would pay to have goggles and a face mask/respirator as part of your grab bag kit that is easy to find in a smoke filled environment. It is absolutely no fun in a smoke filled cabin fighting a fire without these, risk of death is high.
- There should be a way of totally disconnecting the batteries in a hurry. Install a battery post isolator terminal, these only cost $8.00 at Discount Seamart (see picture below). Less than a quarter turn of the green knob and the battery is isolated without damaging cabling.
- Every now and then have a look at individual cables, and wiring looms on the boat when the engine is running and you have the majority of your electrics turned on and check if any are warm. Slow heating of insulation will eventually compromise wiring insulation and it will either melt, or just crumble off the cable it is insulating.
- Try to avoid running high load cables such as anchor windlass, alternator, and feeds to your switch panel together with other cabling. Tying these high load cables to other parts of the wiring loom run the risk of causing secondary damage, and increasing the repair expense.
In summary:
- Check there are no unfused circuits directly connected to the battery;
- Install battery isolators like the one above on all batteries;
- Check for warmth in major cables and bundles of cables;
- Know how to totally turn off all power;
- Know where your cable or bolt cutters are and be able to find them in a smoke filled cabin;
- Have goggles and a mask/respirator, with a suitable filter for smoke fitted, with your grab bag kit.
An electrical fire is relatively simple to control and extinguish, assuming all is correctly connected. It can happen when you least expect it, and like anything on a boat it is subject to Murphy’s Law – it will be likely to happen when you are dealing with other issues. Prepare for it and hopefully you may never see one. If you do nothing else, spend the $8 per battery and have an isolator on your batteries, they would not make them unless there is a demand for them, and do you really want to install one after an event?
