# Dropped Object Impact Analysis Considering Frequency and Consequence for LNG-FPSO Topside Module
## 3 Research Basis  
The FPSO unit can produce and store liquefied natural gas (LNG) in the sea and transfer LNG products through offloading facilities to LNG carriers worldwide. The LNG-FPSO is movable and can be reused in other offshore applications [24].  
In this study, the LNG-FPSO fractionation module was selected for the QRA of dropped objects on the offshore platform [25]. Fractionation is part of liquefaction, as shown in Figure 2. Fractionation was selected because of its high frequency of accidents among the liquefaction processes, and the QRA procedure and results of a heavy weight drop are discussed in this context.  
The fractionation module consists of a process deck, mezzanine deck, and upper deck. The key locations in the module are shown in Figure 3. The first process entails a separation/extraction system. The separation process separates the gas into hydrocarbons C1-C2, C3-C4, and other configurations via a demethanizer and stabilizer, as shown in Figure 2. The second process entails a liquid petroleum gas (LPG) system, where C3 and C4 are stored in respective LPG tanks.  
The maintenance equipment of the module is divided into 15 types, as listed in Table 1. Equipment specifications are subdivided into size, quantity, weight, and force. The heaviest equipment listed in Table 1 is the LPG compressor, and the lightest is the condensate cooler. These specifications are provided by a project named QRA based on design verification technology for highly hazardous accidents of offshore installations (10041090). Figure 4 shows the material handling route for the process deck and upper deck. Table 2 describes the material handling symbols.  
Figure 2: LNG-FPSO production process flow.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Tag**} & \multirow{2}{*}{**Description**} & \multicolumn{3}{c}{**Size (m)**} & \multirow{2}{*}{**Quantity**} & \multirow{2}{*}{**Weight**} & \multirow{2}{*}{**Force**} \\ \cline{3-3} \cline{5-8}  & & **W/Dia** & **L/Dia** & **H** & **(Set)** & **(Ikg)** & **(N)** \\ \hline
1 & Boiler 1 & 0.5 & 4.0 & 0.5 & 1 & 653 & 6409 \\ \hline
2 & Cooler 1 & 0.4 & 1.2 & 0.4 & 1 & 170 & 1669 \\ \hline
3 & Boiler 2 & 7.0 & 4.0 & 0.7 & 1 & 942 & 9237 \\ \hline
4 & Condenser 1 & 0.8 & 4.0 & 0.8 & 1 & 1091 & 10,698 \\ \hline
5 & Pump A/B (1) & 2.1 & 0.8 & 0.8 & 2 & 618 & 6063 \\ \hline
6 & Demethanizer & 1.4 & 1.4 & 12.5 & 1 & 4296 & 42,143 \\ \hline
7 & Stabilizer 1 & 1.1 & 1.1 & 12.5 & 1 & 3369 & 33,047 \\ \hline
8 & Stabilizer 2 & 1.6 & 4.0 & 1.6 & 1 & 2395 & 23,496 \\ \hline
9 & Flash Drum 1 & 2.4 & 2.4 & 6.8 & 1 & 4018 & 39,418 \\ \hline
10 & Flash Drum 2 & 2.0 & 2.0 & 5.9 & 1 & 2903 & 28,477 \\ \hline
11 & Suction Drum & 1.6 & 1.6 & 6.8 & 1 & 2673 & 26,224 \\ \hline
12 & Surge Drum 1 & 2.2 & 2.2 & 5.8 & 1 & 3141 & 30,808 \\ \hline
13 & Condenser 2 & 1.5 & 2.0 & 2.2 & 1 & 1666 & 16,346 \\ \hline
14 & Compressor 1 & 2.7 & 9.6 & 2.7 & 1 & 9260 & 90,840 \\ \hline
15 & Pump A/B (2) & 1.0 & 1.0 & 1.5 & 2 & 619 & 6068 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Maintenance equipment list.  
Figure 3: Overall layout of the fractionation module.