# Comparative Analysis of Marine Alternative Fuels for Offshore Supply Vessels
## 2 Methodology
### Safety Impact  
In this section, an analysis of fuel characteristics, which serve as a critical parameter in terms of safety, and a review of the safety regulations and guidelines for potential alternative fuels are conducted to impart a comprehensive understanding of the safety assessment of various fuel options. A number of crucial inherent characteristics of alternative fuels, including electricity, have a direct impact on the safe application of these fuels onboard. The analysis of these aspects is critical in understanding the safe utilisation of alternative fuels in the maritime environment.  
Table 14 presents an overview of the fuel characteristics of relevant fuels.  
Safety regulations for alternative fuels are developed after the technology reaches technical maturity. Over the past decade, the IMO has established regulations to mitigate risks for marine fuels. Interim guidelines for methanol, ethanol, fuel cells, and LPG have been introduced based on limited operational experience, as seen in Figure 5. These guidelines are expected to be integrated into the IGF Code soon, with additional regulations applied for fuel cells depending on the fuel used.  
The IMO has not yet focused on ship battery use, though this may change with new GHG targets. Development is mostly led by Flag States, such as through the UK's guidelines for lithium-ion batteries. Safety standards for ammonia, hydrogen, and batteries follow MSC.1/Circ.1455, which outlines alternative fuel approvals. The IGF Code requires a HAZID study during design to assess risks. Safety readiness for alternative fuels is evaluated based on two criteria: (a) fuel-specific requirements for handling and storage, and (b) onboard energy systems like propulsion, fuel cells, and batteries. Ships must comply with both, as shown in Figure 6.  
Safety regulations for mechanical and electrical propulsion systems for LNG, methanol, and HFO are available, but regulations for ammonia and hydrogen are still under development. Once fuel-specific requirements are established, mechanical propulsion regulations will apply through the IGF Code or interim guidelines. Electric propulsion systems are  
\begin{table}
\begin{tabular}{p{113.8 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt}} \hline \hline
**Property** & **Ammonia** & **Hydrogen** & **Biodiesel** & **Methanol** & **LNG (Methane)** \\ \hline Chemical formula & NH\({}_{3}\) & H\({}_{2}\) & RCOOCH\({}_{3}\) & CH\({}_{3}\)OH & CH\({}_{4}\) \\ \hline Toxicity & Highly toxic & Not toxic & Not toxic & Low acute toxicity & Not toxic \\ \hline TWA [ppm] & 25 & - & - & 200 & - \\ \hline STEL [ppm] & 35 & - & - & 250 & - \\ \hline \multicolumn{4}{p{113.8 pt}}{} \\ \multicolumn{4}{p{113.  
governed by SOLAS Chapter II-1, which covers electrical power generation. For lithium-ion batteries, this analysis assumes limited application based on UK regulations. Some biofuels have flashpoints between 52 \({}^{\circ}\)C and 60 \({}^{\circ}\)C, with IMO guidelines still in development, meaning full regulatory readiness is not yet achieved.  
The evaluation of the potential risk posed by ship fuel necessitates a thorough examination of its physical properties and characteristics, including toxicity, corrosioness, and flammability. Based on Table 15, the final rating numbers are indicated in Table 16.  
Figure 5: A brief overview of the formulation process in the IMO for IGF Code and interim guidelines.  
Figure 6: Flow chart for evaluation of safety regulation readiness.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Rating Number** & \
\begin{tabular}{c} **Toxicity** \\ **(TWA ppm)** \\ \end{tabular} &
\begin{tabular}{c} **Corrosiveness** \\ **(Range of Flammability, ULF-LFL)** \\ \end{tabular} \\ \hline
5 & 0–200 & Too low & 0–4 \\ \hline
4 & 201–400 & Low & 5–8 \\ \hline
3 & 400–600 & Moderate & 9–20 \\ \hline
2 & 600–800 & High & 21–30 \\ \hline
1 & 800–1000 & Too high & 30- \\ \hline \hline \end{tabular}
\end{table}
Table 15: Rating numbers for fuel characteristics.