The U.S. Coast Guard (USCG), with the assistance and cooperation of the Passenger Vessel Association (PVA), recently completed a fire protection engineering study involving fire testing and computer modeling to validate a USCG policy that allows reductions in structural fire protection between certain areas aboard small passenger vessels.

Fire is a major concern with any type of structure, but especially on a seagoing passenger vessel. When a passenger vessel experiences a fire while at sea, there is no fire department to assist, no public way to exit. The crew is tasked with extinguishing the fire or relying on the structural fire protection and active fire suppression systems to protect the vessel and the passengers on board.

This fire threat, along with many other potential risks associated with seagoing passenger vessels, is the basis for one of many missions of the U.S. Coast Guard, which is to regulate the safety of the small passenger vessel (SPV) industry. The stringent regulations of Title 46 of the Code of Federal Regulations1 (CFR) include numerous requirements applicable to SPVs that include, but are not limited to, hull construction, fire protection, lifesaving, manning, and operations. These requirements can vary depending on the size of the vessel and the number of passengers it carries.

The fire protection aspect of the CFR includes requirements for firefighting equipment, as well as structural fire protection to provide fire boundaries between spaces. This article discusses very low fire load spaces, or so-called "5A” spaces, in particular. The USCG-developed policy regarding these types of spaces is intended to provide relief to the SPV industry from certain structural fire protection requirements, permitting weight savings that directly impact vessel fuel efficiency, capacity, stability, and speed, for spaces with very low, controlled fire loads. Type 5A spaces are commonly found on high-speed ferries or tourist excursion vessels.


The USCG policy ("5A policy” hereinafter) was first established in 1994, and is a relaxation of structural fire protection requirements specified in 46 CFR Subchapter K for A-60 structural fire protection boundaries between certain passenger spaces and areas of refuge, embarkation areas, external escape routes, and other adjacent spaces. Subchapter K applies to a SPV of less than 100 gross tons carrying more than 150 passengers, or with overnight accommodations for more than 49 passengers. "A” class bulkheads or decks are composed of steel or equivalent material capable of preventing the passage of smoke or flame for one hour when subjected to the standard fire test. In addition, they must be insulated with approved structural insulation, bulkhead panels, or deck coverings so that, if subjected to the standard fire test for the applicable time listed below, the average temperature on the unexposed side does not rise more than 139°C above the original temperature, nor does the temperature at any one point rise more than 181°C above the original temperature:

A-60 Class – 60 minutes;

A-30 Class – 30 minutes;

A-15 Class – 15 minutes;

A-0 Class – 0 minutes.

The 5A policy, which allows the use of C-Class (smoke tight and noncombustible) boundaries in lieu of A-Class boundaries, is conditional upon the use of a very-low-design fire load in the 5A space as well as other design and operational requirements. By controlling the fire load, vessel designers and operators are able to use aluminum construction with minimal insulation, thereby reducing vessel weight and increasing operational efficiency. (See Figures 1-3)

Figure 1: 5A Space – Old Style (i.e., non-cushioned seats, small seating area)

Figure 2: 5A Space – New Style (i.e., cushioned seats, large seating area)

Figure 3: 5A Space Example – New Style (i.e., cushioned seats, large seating area)

Since 1994, substantial increases in size, complexity, and furnishings of Subchapter K passenger vessels have raised concerns about the assumptions and safety margins inherent in the 5A policy. At the same time, advances in computational fire modeling capabilities have enabled the Coast Guard and designers to take a more thorough look at the issue. In 2010, Change-1 to the USCG’s Navigation and Vessel Inspection Circular (NVIC) 9-97 "Guide to Structural Fire Protection”2 revised the 5A policy to require designers to submit a performance- based engineering analysis to support the relaxation of fire protection requirements for 5A spaces. Given the potential costs and complexity involved with performing such an analysis, the Coast Guard and the Passenger Vessel Association agreed to form a working group to study this issue with the intent to identify performance guidelines for 5A spaces, which may be accepted in lieu of a full engineering analysis.

Report of Study Overview

The USCG/PVA 5A Working Group developed a method of validating the 5A policy using current fire protection engineering analysis techniques. The validation method completed by the group included the following:

  1. Select a representative 5A vessel for the analysis;
  2. Develop a Fire Dynamics Simulator (FDS) computer model of the test vessel and define the assumptions of the simulations;
  3. Employ a Coast Guard graduate student at the University of Maryland College Park (UMCP) to develop and complete a fire test experiment on select finishing materials and collect heat release rate data for the fire modeling;
  4. Conduct FDS simulations for the test vessel with fire data obtained from the UMCP experiment program and interpret the results; and
  5. Develop performance-based guidelines taking into account the results of the FDS simulations.

Figure 4: Model of 5A space used for simulation. Some seat rows were taken out to reduce clutter for illustration.

Test Vessel and FDS Model

The group selected the M/V IYANOUGH (O. N. 1185366) as the 5A test vessel. This vessel, operated by the Massachusetts Steamship Authority (one of the key operational partners in this working group), was deemed to be representative of the state-of-the-art of current 5A vessels in passenger service. The M/V IYANOUGH is a 144.5-ft. (34.90 m) long aluminum vessel certificated to carry 393 passengers. A two-deck model with an interior staircase and an un-insulated aluminum deck between the two spaces was constructed in FDS to represent the M/V IYANOUGH passenger spaces. Working group representatives from USCG Headquarters, the USCG Marine Safety Center, and Gladding-Hearn Shipbuilding visited the vessel in order to observe arrangements and record the as-built dimensions. The FDS model of the vessel was constructed from the general arrangement plans and the as-built observations and measurements.

UMCP Experiment Program and FDS Computer Simulations

A thesis3 completed by a UMCP graduate student determined the burning characteristics and heat-flux dependent ignition time of certain furnishing materials representing the primary fire loads aboard the M/V IYANOUGH. This data was obtained by completing cone calorimeter testing on the seat cushion foam and fabric provided by the vessel seat manufacturer. (See Figures 5-7)

A majority of the foam used in the seats had a density of 38 kg/m3, a combustible mass of approximately 1.7 kg, and a tear strength factor of 200 N. This type of foam was used for testing and assumed to be the main fire load contributor. A select few other types of foam with slightly different properties were used in the seats in small quantities to prevent excessive compression and provide additional comfort. These foams were not tested because they were assumed not to be a main fire load contributor. The fabric on the seats was available in an assortment of designs and colors, but the type of fabric was a consistent blend of 60% worsted wool and 40% polyester.

The material properties, measured through experimentation, were entered into the FDS model to determine what effects a burning seat cushion would have on other combustibles within the 5A space. FDS simulations of the two-deck M/V IYANOUGH model were conducted via a multi-processor computer using these seat material ignition time data sets.

In conjunction with running the FDS simulations at the exact dimensions and fire load of the M/V IYANOUGH, additional simulations were completed with two and three times the fire load as well as variations in compartment volume and placement of the fire loads. The criteria for acceptable fire performance during the 60 minutes after detection of the fire for the FDS model 5A space were as follows:

  1. The aluminum deck underneath the area of refuge must not reach 200°C over any square meter;
  2. No single point of the deck will reach 400°C; and
  3. The refuge area (second deck of the model) will remain free of smoke.

Figure 5: Foam and Fabric Sample Sustaining Flame After Ignition

Figure 6: Seat Assembly For Full-Scale Testing

Figure 7: Sample Chair Fully Engulfed (left) and a Chair After Extinguishment (right)

Report of Study Results

The experimental program and fire modeling conducted in cooperation with UMCP determined that, without suppression, a fire starting in a single seat will spread to a maximum of 10 seats (two rows of five) for the base case (as built) arrangement. This conclusion is based on:

  1. A fire involving an individual seat (that meets the requirements below) will likely ignite adjacent seats that are less than 12 in (0.3 m) away;
  2. A fire involving a single row of seats (with a maximum of five seats) will likely ignite seats in an adjacent row in a back-to-back arrangement regardless of the angle of the seat;
  3. Rows facing the same direction will not ignite an adjacent row provided the distance between rows is greater than 30 in (0.76 m – measured front to front);
  4. Rows facing each other will not allow fire spread provided the knee gap is greater than 18 in (0.46 m – measured front to front) apart AND tables or other intervening furnishings are "fire resistant” per 46 CFR 116.423;
  5. Carpet or other floor coverings meeting the low flame spread requirements of IMO FTP Code4 Annex 1, Parts 2 and 5 (for floor coverings) will not become involved in a fire originating on seating that meets the requirements of this policy.

These results form the basis for a set of performance guidelines that can be used by industry, as an alternative to a full performance-based analysis to obtain a relaxation of the structural fire protection required for areas of refuge, embarkation areas, and external escape routes. These guidelines are listed in the below.

This report of the study did not address every possible scenario involving the use of 5A spaces aboard passenger vessels. Arrangements not addressed in the guidelines may require additional performance-based analysis.

Space Performance Guidelines

These performance guidelines are intended to guide designers and operators in the design and maintenance of Type "5A” spaces as equivalent to the structural fire protection requirements in 46 CFR Subchapter K. Where NVIC 9-97, Change 1 calls for a performance-based analysis, these guidelines may be used instead.

A. 5A Space Requirements and Conditions

  1. Transient fire load must be controlled:
    1. To prevent a fire from extending past the row of origin.
    2. To prevent the obstruction of aisles or escape paths.
    3. Not to exceed a combustible weight of 0.5 lb/ft2 (2.5 kg/m2).
  2. Seating density and restrictions:
    1. No more than five contiguous seats in a row.
    2. No more than 300 seats in any space.
    3. Seats must be fixed and arranged to comply with 46 CFR 116.820.
    4. A 5A space with an interior or exterior refuge area directly above is limited to a maximum enclosed volume of 24,750 ft3 (700 m3) and a minimum volume of 8,830 ft3 (250 m3).
    5. The minimum acceptable distance between rows facing the same direction is 30 in (0.76 m).
    6. The minimum acceptable distance between rows facing each other is 18 in (0.46 m).
    7. Tables and other intervening furnishings must be "fire-resistant.”
    8. Back-to-back seating arrangements of a maximum of 10 total seats are permitted.
    9. The combustible fire load in the space from construction and outfitting materials must not exceed 5 kg/m2 (1 lb/ft2).
  3. All carpet or other floor coverings must meet the low flame spread requirements of IMO FTP Code Annex 1, Parts 2 and 5.
  4. Primary engine room access must not open to a 5A space or any corridor directly accessing a 5A space.
  5. The following conditions must be met per NVIC 9-97, Change 1, Section 4.2:
    1. Fire load calculations, in accordance with section 4.3 of NVIC 9-97, Change 1, must be used to demonstrate compliance with the limits set in this guideline.
    2. Any installed interior finishes or trim must be approved.Any installed interior finishes or trim must be approved.
    3. Furniture and furnishings, draperies, curtains, rugs, and carpets must be fire-resistant in accordance with 46 CFR 116.423.
    4. Any aluminum frame windows fitted in the bulkheads used to separate refuge areas, lifeboat embarkation stations, or escape routes from type 5A spaces must be either Coast Guard-approved A-0 windows, or provided with steel retaining clips. Ordinary glass (tempered or laminated) with steel clips is acceptable for the exterior bulkheads of 5A spaces located below or adjacent to areas of refuge.
    5. The aluminum deck of a 5A space does not require top-side A-class insulation.
    6. A USCG-type-approved fire detection and manual fire alarm system must be installed in accordance with 46 CFR 118.400. Smoke detectors must be fitted in all accommodations, control stations, and service spaces.
    7. A fire pump and fire main system complying with 46 CFR 181.300-320 must be installed for vessels greater than 65 ft (19.8 m).
    8. The shell plating and framing below the main deck must be A-0 construction for a distance that extends at least 12 in (0.3 m) below the lightest load waterline. Insulation is not required for voids and fuel tanks that meet conditions (i) and (j) below.
    9. Fuel tank boundaries may be un-insulated aluminum or steel construction, provided they meet USCG conditions.
    10. Voids and other spaces where the fire load does not exceed 0.5 lb/ft2 (2.5 kg/m2) and constructed of steel or aluminum do not require insulation.
    11. Stairs and ladders located entirely within a type 5A space or stairs located entirely within a stair tower enclosure may be constructed of un-insulated aluminum or steel.
    12. 5A vessels may be allowed excursion permits if the proposed function is within the approved arrangement and fire load assumptions.
    13. In public areas, one A-II portable fire extinguisher must be provided for every 500 ft2 (45 m2) of deck area or fraction thereof.
  6. Seat construction restrictions:
    1. Must have noncombustible frames.
    2. Total combustible weight of each seat must not exceed 3.85 lb (1.75 kg).
    3. Cushions and upholstery must be tested and determined to be fire-resistant in accordance with USCG NVIC 9-97, Change 1, Section 4.2.

B. Equivalence Allowed (Provided the requirements and conditions listed above are satisfied, the following arrangements may be accepted.)

  1. Boundaries between 5A spaces and refuge areas may be non-combustible and smoke tight (C-Class) in lieu of A-0 bulkheads required by 46 CFR 114.400.
  2. Up to 0.5 lb/ft2 (2.5 kg/m2) of the weight of floor coverings that meet the IMO FTP Code Annex 1, Parts 2 and 5 may be excluded from the 1 lb/ft2 (5 kg/m2) fire-load limit.
  3. Stanchions within a 5A space that support a deck between two 5A spaces may be of un-insulated aluminum construction.
  4. Bathrooms with a single toilet and sink with vanity, which do not have storage provisions for other materials, may be considered part of the space in which they are located, and not necessarily a separate Type 8 space.
  5. Consistent with the treatment of areas of refuge on other U.S. passenger vessels, the space above need not be considered an area of refuge for the purposes of a fire in a space, if there is sufficient refuge located elsewhere on the vessel.

LCDR John H. Miller is with the U.S. Coast Guard.


  1. Title 46, Code of Federal Regulations, Government Printing Office, Washington, DC, 2014.
  2. Navigation and Vessel Inspection Circular (NVIC) 9-97 "Guide to Structural Fire Protection,” Change 1, U.S. Coast Guard, Washington, DC, 2010.
  3. Shriner, N. ”Fire Growth Evaluation for Regulations of Fire Load for Type 5A Spaces on Seafaring Vessels.” MS Thesis, Department of Fire Protection Engineering, University of Maryland, College Park, 2012.
  4. Fire Test Procedures Code, International Maritime Organization, London, 2010.