Question: The photo I sent in is the fire extinguisher “port” location under one of the companionway steps on my cruising sailboat. After a close inspection and comparing the diameter of the port with the nozzle on the fire extinguisher on board I find that I have a major mismatch.

The fire port won't be of use if the extinguisher nozzle can't fit through, or if the extinguisher is meant to be aimed directly at the base of the fire.

The fire port won't be of use if the extinguisher nozzle can't fit through, or if the extinguisher is meant to be aimed directly at the base of the fire.

Furthermore, the extinguisher I have, which was provided as a part of a “safety kit” when I bought my boat, is a dry chemical extinguisher. If I’m not mistaken it is somewhat directional in use, meaning that to work properly you need to point it at the base of the fire in question.

Since this port is located high on the bulkhead section of my companionway, I can’t really conceive of how I could even aim a dry chemical extinguisher at the base of a fire in my engine room space on the other side of this port. A friend told me that this sort of configuration is intended for a “clean agent” type of fire extinguisher. I’ve checked online and these are super expensive compared to the dry chemical units. Do you have a solution that is not going to break the bank?

Answer: Oh boy, this opens up a can of worms! You are quite observant and it’s a good thing. This is an all-too-common mistake on the part of your dealer. The port is actually a requirement under both ISO and ABYC safety standards that deal with on-board firefighting systems. The label next to your port speaks to part of the problem here. Basically, the standards want you to fight fires from outside the space where the fire is. The thinking here is that opening the hatch, door or access to the space will add fresh oxygen to the area and give the fire more of the fuel it needs to burn, exacerbating the problem.

Your assessment of the situation is correct: Even if you could get the nozzle of your dry chemical extinguisher through the port, you still couldn’t aim it properly. The clean agent extinguishers that these ports are designed to be used with basically smother the fire by eliminating the oxygen in the space. So, with that type of extinguisher, aim is not critical; what is critical is that the extinguisher has enough agent capacity to completely smother and consume all of the air in the space the fire is located in. So, the bottom line there is that size matters very much with these extinguishers. The table shown here, which comes from ABYC Standard A-4, can help in determining how large the extinguisher on your boat needs to be.



1. The above results in concentrations of 45% CO2at 70ºF (21ºC) based on 0.075 lbs Agent/ft3or 5% Halon at 70°F (21°C) based on 0.023 lbs Agent/ft3.

2. "Halon" is Halon 1211, Halon 1301, or a mixture thereof.

To determine compartment volume:

Compartment volume shall be at least gross volume less that of permanently installed tankage. For most sailboats, the fuel tank is not located in the engine room space, but there could be a water heater tank in the same space, so its volume would be deducted from the total.

So, now to the expense side of all this. As a point of comparison, one popular online source that sells marine equipment exclusively sells a 10-lb. dry chemical extinguisher for $24. This is usually what dealers throw into their “safety packages”. An 11-lb. Fireboy clean agent unit from the same vendor sells for just under $500! The case in point is to study that table. A little bit of Halon clean agent goes much farther than CO2, as you can see. A 10-lb. C02 extinguisher can be found online for about $230, so about half the price of the Halon types. I see that as about the only way to save money in this case. Just make sure the extinguisher nozzle size is a good match for the port size. I’ve seen larger port fittings available for about $12 that could accommodate a larger nozzle, so that could also be a solution.