2.1 Laminates, sandwich panels and stiffeners formed by polymers, fibres and core
materials may be combined in different ways to make up FRP elements on ships. Within
these guidelines, FRP is defined as multi-material compositions of monolithic or
sandwich constructions. Monolithic constructions and skin layers of sandwich
constructions are based on long-fibre reinforced resins. Reinforcements can be for
example fabrics of glass, carbon, aramide or basalt fibres. Resins shall be based on
duromer (thermoset) resin. Sandwich core materials are typically based on structural
foams or honeycombs. Coatings (gelcoats, topcoats or paints), casting masses and
adhesives are handled under these guidelines as well. Some typical FRP composite
materials and compositions used in shipbuilding are further described in appendix B
(FRP composite materials and compositions used in shipbuilding). It also exemplifies
fire behaviour of typical FRP composite constituents and compositions. Relevant fire
properties of the particular materials considered in an alternative design must be
derived by tests for each specific design case (see appendix D (Fire testing of FRP
composite)).
2.2 Use of FRP composites on SOLAS
vessels is generally not allowed due to prescriptive requirements on use of
non-combustible materials. However, when design or arrangements deviate from the
prescriptive requirements of SOLAS chapter II-2, review and approval can be carried out in accordance
with SOLAS regulation II-2/17. Combustible FRP elements and related safety measures
can thus be treated as alternative fire safety design and arrangements. Engineering
analysis, evaluation and approval shall then be carried out based on a procedure
summarized in the regulation, whilst more detailed descriptions are contained in the
Guidelines on alternative design and arrangements for fire safety (MSC.1/Circ.1002, as amended by MSC.1/Circ.1552). Life safety performance criteria are contained in
MSC.1/Circ.1552. These guidelines support the use of performance-based
methods of fire safety engineering to verify that the fire safety of a ship with
alternative design and arrangements is equivalent to the fire safety stipulated by
prescriptive requirements, a concept often referred to as the "equivalence
principle". Briefly, the procedure can be described as a two-step deterministic risk
assessment carried out by a design team. The two major parts to be performed
are:
- .1 the preliminary analysis in qualitative terms; and
- .2 the quantitative analysis.
In the first part, the design team is to define the scope of the analysis, identify
hazards and, from these, develop design fire scenarios as well as develop trial
alternative designs. The different components of the preliminary analysis in
qualitative terms are documented in a preliminary analysis report which needs
consent by the design team before it is sent to the Administration for review. With
the Administration's approval, the preliminary analysis report documents the inputs
to the next step of the assessment, the quantitative analysis. At this stage, the
design fire scenarios are quantified and outcomes are compared with performance
criteria determined based on the fire safety objectives and the functional
requirements of the SOLAS regulations. The criteria are quantified with reference
to relevant prescriptive requirements or by comparison to the performance of an
acceptable prescriptive design. The documented level of fire safety of the
alternative design and arrangements may therefore not be absolute but relative to
the fire safety of a traditional design, which is a product of the fire safety
implied by prescriptive regulations. Accounting for uncertainties when comparing
levels of fire safety, the final documentation of the engineering analysis based on
SOLAS regulation
II-2/17 (hereafter referred to as "SOLAS regulation
II-2/17 assessment") should with reasonable confidence demonstrate that
the fire safety of the alternative design and arrangements is at least equivalent to
that of a prescriptive design.
2.3 According to SOLAS regulation II-2/17, alternative design and arrangements for
fire safety should provide a degree of safety at least equivalent to that achieved
by compliance with the prescriptive requirements. It is therefore important that the
approach used to assess safety can properly describe the effects on fire safety
posed by the alternative design and arrangements, i.e. descriptions of uncertainties
must be sufficient to establish appropriate safety margins. This is a particularly
relevant consideration when evaluating FRP composite structures. Depending on the
scope, an assessment in accordance with MSC.1/Circ.1002, as amended by MSC.1/Circ.1552, could appear overly complex or insufficient.
Recommendations and requirements for the method used to assess the safety of an
alternative design involving FRP composite structures are discussed in appendix C
(Recommendations regarding the assessment). It may also be relevant to consider the
Guidelines for the approval of alternatives and equivalents as provided for in
various IMO instruments (MSC.1/Circ.1455), which describe an approach which is more adaptable to
the scope of the alternative design and arrangements. MSC.1/Circ.1455 was developed to provide a consistent process for the
coordination, review and approval of alternative design and arrangements in general,
i.e. not only concerning fire safety. It may therefore provide additional guidance
when the use of FRP composite structures affects other aspects of safety than those
related to fire (see appendix A (Issues other than fire safety)). In detail it also
describes the risk-based approval process surrounding the assessment. As referred to
in SOLAS, the guidelines in this document take basis in MSC.1/Circ.1002, as amended byMSC.1/Circ.1552.
2.4 One of the first and most foundational steps in the SOLAS regulation
II-2/17 assessment is to form an approval basis. This is done by
identifying the prescriptive requirement(s) deviated by the alternative design and
arrangements (SOLAS regulation II-2/17.3.2). With an understanding of their
associated functional requirements, the deviated prescriptive requirements are then
used to define performance criteria, as described in MSC.1/Circ.1002, as amended by MSC.1/Circ.1552, paragraphs 4.4, 5.1.2 and 6.3.2 and in SOLAS regulation
II-2/17.3.4. However, owing to limitations in the current regulations,
identification of deviated prescriptive requirements may not form a sufficient basis
to ensure equivalent safety. When considering FRP composite structures, deviations
fundamentally concern the required non-combustibility of structures. With the
assumption that non-combustible structures are used, the fire safety regulations
include unwritten (implicit) safety requirements. In order to establish an
appropriate approval basis, it is therefore required in each design case to perform
the necessary investigations to identify all relevant effects on fire safety. This
is further described in appendix C (Recommendations regarding the assessment). In
particular, the achievement of each fire safety objective and functional requirement
should be judged independently, including the functional requirements in purpose
statements at the beginning of the regulations. Potential challenges to fire safety
objectives, functional requirements, purpose statements and prescriptive
requirements in SOLAS chapter II-2 when considering FRP elements are
exemplified in chapter 3 (Important factors to consider when evaluating FRP elements
with starting point in the regulations of SOLAS chapter II-2). Further recommendations regarding an assessment of
fire safety involving FRP elements are presented in appendix C (Recommendations
regarding the assessment).
2.5 A number of fire hazards may be introduced by the use of FRP elements. A useful
starting point for the hazard identification is the investigation of challenges to
regulations and thus chapter 3 (Important factors to consider when evaluating FRP
elements with starting point in the regulations of SOLAS chapter II-2). Fire hazards relevant for further investigation,
categorized according to the regulations in SOLAS chapter II-2, are particularly:
- .1 probability of ignition;
- .2 fire growth potential;
- .3 potential to generate smoke and toxic products;
- .4 containment of fire;
- .5 firefighting; and
- .6 structural integrity.
2.6 The fire hazards and performance of safety measures may be quantified by tools
for fire safety engineering and risk assessment and with reference to fire tests
(see appendix D (Fire testing of FRP composite)). Sufficient safety may be assured
within delimited areas separately, e.g. covered by functional requirements or
regulations, or included in a holistic estimation of effects on safety. The former
is illustrated along with further examples of an assessment in appendix E
(Assessment examples).
2.7 Key terms are defined in MSC.1/Circ.1002, as amended by MSC.1/Circ.1552, and MSC.1/Circ.1455, as well as in fire safety engineering guidelines for
buildings, e.g. ISO 23932.