# Modelling Prefabricated Construction Safety
## 3 Results and Discussion
### Injuries in Prefabricated Construction Accidents
#### 3.6.3 Injury Prior Activity  
Figure 14 shows the number of accidents under prior activity to cause injury in PCC. The X-axis represents the years and the y-axis represents the percentages of occurrence. Overall, the most common prior activities to cause injury is 'employment tasks' (44%), followed by 'lifting/lowering/loading/unloading' (21%) and 'unknown' (21%). Interestingly, the remaining are less than 11%. Overall, 'employment tasks' is the most common prior activity in all type of PCC (business classification). However, 'unknown' surpasses the rest, indicating the lack of clarity around reporting the injury. Only the prior activity of 'getting on/off/in/out of' is associated with Conc. A huge gap has been observed in 'employment tasks' (54%) in comparison to the other prior activities for Metal_P. In the last five years, declines have been observed for 'employment tasks' and 'walking/running', but a slight increase was observed in 'lifting/lowering/loading/unloading' and 'ascending/descending'. There is more variation in 'using/operating (no machine)' as a prior activity. Understanding of injury through prior activity and associated risks determination is essential for safety assessment [21]. Figure 13: ARIMA models for accident forecasting by injury causes (2017–2027). According to Figure 15, in comparison to onsite construction, 'employment tasks' (39%) are relatively lower, as well as workers involved in 'lifting/lowering/loading/unloading' (14%) and 'using/operating (no machine)' (10%). This indicates using tools and plants are relatively safer in an offsite construction environment. However, for the 'unknown' (21%) category, prior activities are more frequent. Offsite, four times fewer accidents were reported for 'employment task', three times for 'lifting/lowering/loading/unloading', six times for 'using/operating (not machine)', four times for 'walking/running', but were almost similar for 'ascending/descending'. Injury prior activities were modelled with simplistic equations to determine the weightage of each prior activity under each classification. This helps to determine the critical prior activities to accidents, and is useful to design work methods, manage, and schedule activities. \[\text{Injury prior activity (Wood\_S)}=40\ \times\ \text{Employment tasks + 21 $\times$ Lifting/lowering/loading/unloading +}\\ 8\ \times\ \text{Using/operating + 4 $\times$ Walking/running + 4 $\times$ Ascending/descending + 26 $\times$ Other} \tag{28}\]  
\[\text{Injury prior activity (Conc)}=44\ \times\ \text{Employment tasks + 11 $\times$ Lifting/lowering/loading/unloading +}\\ 6\ \times\ \text{Using/operating + 5 $\times$ Walking/running + 3 $\times$ Getting on/off/in/out of + 31 $\times$ Other} \tag{29}\]  
\[\text{Injury prior activity (Alum)}=40\ \times\ \text{Employment tasks + 25 $\times$ Lifting/lowering/loading/unloading +}\\ 5\ \times\ \text{Using/operating + 4 $\times$ Walking/running + 2 $\times$ Ascending/descending + 24 $\times$ Other} \tag{30}\]  
Figure 14: Number of accidents by prior activity to injury in prefabricated construction (2017–2022). In this section, accident frequency is forecast for the injury prior activity. Table 6 and Figure 16 show the optimized ARIMA models for each prior activity. The main trend is that 'using/operating (not machine)' is declining, but the rest are somehow increasing, except for 'lifting/lowering/loading/unloading', which has relatively steady trend. 'Employment task (not classified elsewhere)' is the most critical, having a somehow gradual increase in the next five years. This highlights the need for standard operating procedures to be strictly followed. There is no model for 'Walking/running' and 'Getting on/off/in/out of', as all models have negative R\({}^{2}\).