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Fixed Fire Extinguishing Systems for
Small Passenger Vessels (T-Boats)

This site provides information on the types of fixed fire extinguishing systems that can be installed onboard a Small Passenger Vessel inspected under Title 46 of the Code of Federal Regulations (46 CFR) Subchapter T, as well as information on choosing a fixed fire extinguishing system and main engine shut down options.

Page Index:

  1. Types of fixed firefighting systems.
  2. Choice of extinguishing system.
  3. Engine shutdown options.

1. Types of Fixed Firefighting Systems

Custom engineered systems

These are type approved systems originally intended for manned spaces on large vessels, but include scaled-down system configurations suitable for installation in unmanned spaces such as engine compartments on Subchapter T vessels. They include carbon dioxide systems (approval category 162.038), new clean fire extinguishing agents such as FM200 (approval category 162.161), and halon (approval category 162.035). There are no new halon systems because halon is no longer manufactured due to environmental concerns.

These systems are type approved after initial testing by an independent testing lab (Underwriters Laboratories) and are described in the manufacturer's approved design, installation, operation and maintenance manual. They are called "engineered" or "custom engineered" because they are specifically designed for each vessel's engine room by amount of agent, pipe lengths, pipe sizes, nozzle size, number of nozzles, etc. The system manufacturer's distributor (not the vessel operator) designs these systems by entering a vessel's engine room dimensions into the manufacturer's computer program, which calculates the amount of agent, number of agent cylinders, pipe sizes, and number and size of nozzles, etc., needed to protect the specific engine room. The system components must be selected from the manufacturer's approved manual.

Manufacturers of custom engineered systems are issued certificates of approval, which can be found on-line at CGMIX.

The review of these systems is conducted primarily by the Coast Guard Marine Safety Center.

Pre-engineered systems

These are type approved systems originally designed for pleasure craft engine compartments as automatic systems, but many models are suitable for many Subchapter T applications because they are equipped with manual backup actuators and provisions for ventilation and engine shutdowns. They are called "pre-engineered" because they are tested by an independent testing lab (UL or FM) to extinguish a fire in a simulated engine compartment of the maximum volume which they are intended to protect. Unlike custom engineered systems, a pre-engineered system can be installed in any unmanned engine room of equal or lesser gross volume in accordance with the limitations described in its owner's manual.

The systems are intended to be an "off the shelf" item suitable for installation by either a fire equipment distributor or the vessel's operator. The systems currently type approved are simple, consisting of a single agent cylinder with attached valve, and are attached to a bulkhead inside the engine compartment. Currently approved systems have no discharge piping, the agent being discharged directly from the cylinder valve through the attached sprinkler head when the heat from a fire causes the sprinkler head to actuate. The agents include clean agents FM200 and FE241 (all under approval category 162.029), and carbon dioxide (although no systems are currently being marketed). The systems must be installed and maintained in accordance with the manufacturer's approved owner's manual.

Manufacturers of pre-engineered systems are issued certificates of approval, which can be found on-line at CGMIX.

These system installations are reviewed and approved by the Coast Guard Officer in Charge Marine Inspection (OCMI) on a vessel-by-vessel basis.


If the machinery space of the Subchapter T vessel can be protected by the contents of one portable or semi-portable fire extinguisher, such an extinguisher may be used as a fixed gas fire extinguishing system subject to the requirements found in 46 CFR 181.400(b)(5). However, portable and semi-portable extinguishers may not be converted into fixed systems by replacing components such as valves, hoses and nozzles with miscellaneous valves, piping, etc., for the following reasons:

1. Such modifications void laboratory (Underwriters Laboratories (UL) or Factory Mutual (FM)) listings and Coast Guard type approvals. Also, manufacturers will deny responsibility when injuries occur or the modified equipment does not extinguish a fire.

2. There is no guarantee that the modified equipment will work. Fire extinguishers obtain their UL or FM Listings and CG type approval after undergoing extensive tests and quality control inspections. They're approved as a unit (as they leave the factory). Field modifications do not have the benefit of having undergone such tests.

3. Modifying fire extinguishers is inherently dangerous to the persons doing the modifications because it involves high pressure cylinders (the pressure inside a CO2 extinguisher is 850 psi at 70 degrees F (5900 kPa at 21 degrees C)). That's why DOT requires organizations servicing high pressure cylinders to be DOT certified.

It is possible to use portable and semi-portable extinguishers to flood engine compartments in lieu of using a fixed system by following these guidelines:

A portable extinguisher attached to the outside of the engine compartment can be discharged through a closeable discharge port into the protected compartment. The method of attachment should permit the nozzle to be inserted into the discharge port during a fire. The discharge port must be sized to accommodate the extinguisher nozzle. This procedure is also used on pleasure craft as an (second best) alternative to fixed systems protecting small volumes (American Boat and Yacht Council (ABYC) Standards, Chapter A-4), where a portable fire extinguisher is attached by its bracket next to the discharge port. This concept has been shown to be a viable concept for small engine compartments through tests by ABYC committee members and Coast Guard R&D Report No. CG-D-31-76.

The situation with semi-portable extinguishers (46 CFR 162.039 defines them as extinguishers exceeding 55 pounds (25 kg) in gross weight) is more complex in view of the greater amount of CO2 used (currently up to 100 pounds (45 kg)), and the larger spaces this amount of CO2 can protect.  They are permitted where they can supply the amount of CO2 needed for total flooding as determined by the OCMI. However, to work properly, the nozzles must distribute the agent uniformly throughout the space. For the engineered CO2 systems they are intended to replace, the reach of CO2 from a single nozzle is about 10 feet (3 m). Nozzles for engineered systems are spaced uniformly throughout the space in order to achieve a uniform extinguishing agent concentration. As a result the use of semi-portables (which have only one nozzle) should be limited to situations where a one-nozzle system would suffice, i.e. the distance from the nozzle to the compartment end should not exceed 10 feet (3 m). The volume of the space so protected should therefore be not more than 1000 cubic feet (28 cu m). It is also not acceptable to hang the hose into the protected compartment and rig the spring-loaded valve at the end of the hose to stay open. The rubber hoses and plastic nozzles have not been subjected to any relevant testing and are not expected to withstand a fire exposure.

The semi-portables must not be modified, by replacing valves, hoses and nozzles which are supplied as an integral part of each semi-portable with different valves, fixed pipe, and different nozzles. Any semi-portable systems that have been so modified are to be considered custom-engineered systems and must be specifically approved by the Coast Guard in accordance with 46 CFR 181.410.

In view of the great variety of engine compartment designs and fire protection equipment available it will not be possible to provide specific guidance applicable to all situations encountered in the field. The above may be used as general guidance to be applied to the extent local conditions permit. Unusual situations must be addressed on a vessel-by-vessel basis. For example, where the large and irregular shape of the protected space does not permit the above mentioned nozzle coverage, or where the space has a significant amount of uncloseable openings, additional CO2 may be supplied as compensation to ensure that the CO2 in the space can reach extinguishing concentrations.

2. Choice of Extinguishing Systems

An operator of a subchapter T vessel that is required to install a fixed gas fire extinguishing system has several alternatives.

    * The operator may choose a system that will alert him or her to a fire through a fire detection system prior to the operator discharging a manual fixed system


    * The operator may install a completely automatic system that discharges the fixed system upon detection of a fire without any interaction from the operator.

While automatic mechanical ventilation shut-off is required on all custom and pre-engineered fixed gas fire extinguishing systems, an automatic engine shutdown is not. The automatic shutdown of propulsion machinery is only required when the fixed gas fire extinguishing system is activated and when the machinery draws its intake air from within the protected space. However, a dedicated intake air duct to all propulsion machinery from outside the protected space eliminates the need for an automatic engine shut-off switch. The requirement for automatic shut-off switches stems from two facts: that propulsion machinery or mechanical ventilation of the protected space may deplete the extinguishing agent before it is able to perform its function; and that most engine room fires are caused and/or fed by fuel or lubricating oil. An automatic shut-off may also prevent damage to the propulsion machinery from intake of an extinguishing agent and allow an expeditious restart of the propulsion machinery after extinguishing the fire.

3. Engine Shutdown Options

The various engine shut-down options available are explained below:

1. If the machinery space of the subchapter T vessel can be protected by the contents of one portable or semi-portable fire extinguisher, such an extinguisher may be used as a fixed gas fire extinguishing system subject to the requirements found in 46 CFR 181.400(b)(5). When installing a fixed system such as this, a fire detecting system per the requirements of 46 CFR 181.400(c) is also needed. This allows for complete manual control of the fixed gas fire extinguishing system by the operator of the vessel. Marking instructions required by 46 CFR 185.612 direct the operator to secure ventilation and machinery prior to the discharge of the fixed system.

2. A custom-engineered fixed gas fire extinguishing system may be installed in a subchapter T vessel in accordance with 46 CFR 181.410. It is installed as a manual system activated by the operator following the indication of a fire from a fire detection system in the protected space. If the propulsion machinery draws intake air from within the protected space, mechanical ventilation is automatically shut off following the fixed system's activation by the operator.

3. A subchapter T vessel operator may install an "off the shelf" pre-engineered system in accordance with 46 CFR 181.420. This system will automatically shutdown propulsion machinery (that draws air from the protected space), and mechanical ventilation without any interaction from the operator. Some manufacturers provide a spring activated manual override switch that permits the operator to maneuver his vessel out of danger before initiating the shutdowns and subsequent discharge of the fixed gas fire extinguishing system.

4. Subchapter T was written assuming that Clean Agents would be the preferred extinguishing agents for these vessels since less of these agents, as opposed to CO2 , is needed to accomplish the same task. The thinking was that most small passenger vessels lacked sufficient space to accommodate CO2 cylinders. Since Clean Agents may be consumed by the engines, depleting the concentration to a point that it would not extinguish a fire, the requirement for an automatic shut down of the engines was included in the regulations. CO2, when ingested by an engine, will shut down the engine effectively serving as a shut down device. Therefore, operators who choose CO2 as the extinguishing agent may forgo the installation of a separate device to shut the engines down. This action may be taken under 46 CFR 175.540 as an equivalency.

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Last Modified 1/12/2016