Question: Here's a photo of the plastic plug and diagram of a fire extinguisher located on the companionway steps of my new(ish) cruising sailboat.

The pop-out plug between these companionway steps allows a boat owner to fight an engine fire with a portable extinguisher without having to open the whole compartment.

The pop-out plug between these companionway steps allows a boat owner to fight an engine fire with a portable extinguisher without having to open the whole compartment.

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I’m told by the folks at my marina that the hole there is to insert a fire extinguisher in if a fire were to occur in the engine area of my boat. This is provided so that I don’t have to lift the engine access hatch, which on my boat consists of lifting up the entire companionway step area. I’ve checked all the extinguishers on my boat and I can’t find one that has a nozzle that will fit into that hole when I pop out the plastic plug. What’s up with this?

Answer: Great question and good job on your part checking this out! I’ll bet you’re not the only person out there with this potential problem. Most folks are also probably using the much less expensive dry chemical or CO2 extinguishers, too, which can be very damaging to modern engines.

That hole is actually a requirement under both ABYC and European ISO Standards. Yes, it is a port whose purpose is to provide a spot to insert an extinguisher nozzle if a fire were to occur. This is important, as trying to open the engine cover is potentially quite dangerous as it will only add more oxygen to the fire, and it is time-consuming. But, as you have learned, the extinguishers on board need to have a nozzle that will fit into the hole provided.

It's also better to use an extinguisher that utilizes one of the potentially less damaging and environmentally safe extinguishing agents. These extinguishers are available at all of the major suppliers, and will use extinguishing agents like HFC 227 (FM 200) or Novec-1230 or Halotron 1. These are known as "clean agents" and are much less likely to damage any of your boat’s equipment.

The other important point here is that the extinguisher you select needs to be sized appropriately foryour engine compartment. This can be determined by measuring the width, height, and depth of the engine compartment and multiplying those numbers to establish the cubic volume. Standards allow for the deduction of the volume of any tankage within that space, which on most sailboats will not be a consideration as the fuel and water tanks are not generally located in engine room spaces. With clean agents, as mentioned above, a USCG B-1 sized extinguisher will be adequate for a space up to 125 cubic feet. For larger engine room spaces, a USCG B-2 sized extinguisher may be needed. One of those can handle a space up to 250 cubic feet.

For safety reasons, it’s important to remember that the use of portable extinguishers for fighting engine room fires is less desirable than using a fixed-mount system installed in the engine room. Some of the good reasons for this are highlighted here:


  • - Agent distribution may not be satisfactory.

  • - The rate of agent discharge may not assure that an effective extinguishing concentration is achieved.

  • - Fire detection and appropriate action is dependent upon an operator being present and making the correct decisions.

  • - The operator must assure that discharge of the agent is continuous and complete.

  • - Longer discharge time may cause an increase of toxic by-products generated during extinguishment.

  • - The potential for operator injury may be greater.


ABYC Standard A-4 covers both portable and fixed fire-fighting systems.

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