**1. Introduction**

In the early 2000s, the Maritime Safety Committee (MSC) of the International Maritime Organization (IMO) adopted the item goal-based new ship construction standards (GBS) [1], which present new ship design and construction concepts for the long-term organizational work plan. They then developed safety level approach (SLA)-based GBS that are applicable to all ships [2]. The IMO has since actively strengthened the Safety of Life at Sea (SOLAS) standards based on the GBS to reduce the underlying causes of marine accidents and environmental pollution from ship construction and to prioritize ship safety [3].

To assess safety in the ship construction stage, a hazard identification and risk analysis (HIRA) is conducted to identify and evaluate the risk of the system installed in a ship. Specific evaluation

methods for analyzing hazards in HIRA include hazard identification (HAZID), hazardous operability (HAZOP), what-if/checklist, and failure mode and effects analysis (FMEA) [4].

FMEA, a type of risk assessment method, was developed for the Apollo project by the National Aeronautics and Space Administration (NASA) in the mid-1960s. Since then, three major US automakers have introduced their own assessment system "QS-9000" [4]. However, FMEA is the most common way to evaluate device reliability [5]. It is a preventive reliability assessment method performed at the design stage for system or component changes, and it uses an empirical perspective for the analysis and component changes to achieve the optimal results. It is extensively used to assess the design, process, and system risks across all industries including the shipbuilding and marine sectors.

FMEA is advantageous in that it enables systematic analysis using simple methods. The evaluation criteria for the expected severity, occurrence, and detection are established using the risk priority number (RPN) technique, and the failures for individual components are assessed [5,6]. These results are combined to obtain the criticality. However, the logic is inferior to other methods because it uses a qualitative evaluation, and the evaluation results may vary depending on the experience or inclination of the evaluator assessing the failure.

Researchers have performed various studies to increase the objectivity of FMEA. Research has been conducted on an approach combining FMEA and the Boolean representation method (BRM) [7], a method that describes the elements required for FMEA and then develops and applies an appropriate FMEA form for an effective evaluation. Studies have also used a computer system method that supports FMEA evaluations on the Internet [8], the risk priority ranks (RPR) approach to prioritize failure modes [9], a method based on fuzzy logic that considers the interdependence between various failure modes [10–14], a fuzzy-based FMEA performance improvement method using GRAY relationship theory [15], and a method that provides a framework for automatically generating FMEA from past FMEA data using functional inference techniques [16]. Research has additionally been conducted on how to most effectively apply the FEMA system due to difficulties related to its numerous subsystems and the lack of consideration for the indirect relationship between the components in the RPN technique.

In particular, in recent years, in order to apply environmentally friendly ships, ships using hybrid fuel cells, batteries, etc. are being operated mainly on small coastal ships. These vessel systems are very different from the diesel engines used as conventional ship power sources, so new FMEA evaluation criteria and items should be provided to evaluate the safety and reliability of such vessels. However, even in shipyards that are currently building vessels, FMEA evaluation criteria or items have not been specifically set.

Therefore, in this study, the proposed FMEA was conducted to secure the safety and reliability for applying the fuel cell-based (molten-carbonate fuel cell (MCFC; 100 kW), battery (30 kW), and diesel generator (50 kW)) test bed to the actual ship. We analyzed various problems in evaluating RPN, which is mainly used in FMEA, and formed an FMEA expert team to select evaluation criteria and items. As a result, we developed a worksheet applying the reestablished RPN evaluation criteria, and applied Kendall's coefficient of correspondence to the existing evaluation results and the reestablished evaluation results for objective determination of the reestablished evaluation criteria. It was confirmed that the reestablished assessment in the FMEA evaluation of the combined power source showed more reliable results. In addition, the criteria for establishing countermeasures based on the results of the FMEA were prepared, and the proposed evaluation method was found to be effective for the application of the assessment of the safety and reliability of the combined power source.

#### **2. Theoretical Background of FMEA and RPN Introduction**

#### *2.1. What is FMEA?*

FMEA was first used in the NASA Apollo project in the 1960s. In 1974, it was used to develop United States Navy missiles and was established as the United States MIL-STD-1629 standard. Afterwards, the QS-9000 standard was established by the United States automobile industry, and FMEA was introduced in all industries, including shipbuilding [4]. The FMEA method prioritizes resources,

ranks risks, and creates an activity and control plan to analyze the target system [5,6], thereby analyzing failure types and their influence and examining improvement measures with consideration of criticality [17].

The objectives of FMEA are as follows:


Figure 1 illustrates the typical FMEA process.

**Figure 1.** Block diagram of the typical failure mode and effects analysis (FMEA) process.
