in the future if appropriate countermeasures are to be taken.
Figure 3 Estimation of Mean Rig Age
4. Estimation of Accidents due to Insufficient Maintenance
Accidents are classified into 21 types as shown in Table 1 [1], by code and shorttext. Detailed explanation of each type is same as in reference 2.
Figure 4 Relation between Rig Age and Number and Rate of Accident
Usually an accident, which occurs in the reality, is a event of accident sequence, such as ST-LI-CA(structural damage followed by list and then final capsize)as in the case of Alexander L.Kielland [5]. So one "accident" can be classified into several types of accident.
Figure 4 shows the relation between rig age against
Table 1 Type of Accident
number of accidents(relative presentation assuming that number of accidents for 0-1 year old is 100)and also against accidents rate based on data of reference 1. For the calculation of accident rate, number of same age rig is summed up all over the period of statistics and the number of accidents for corresponding age is devided by summation of rig number of corresponding age. Initial high accident rate rapidly decreases till 10-11 years old but after that it starts to increase till it shows its peak value at age of 14-15 years old then it decreases again till the final increase after 26 years old.
Figures 5 through 8 show the relation between rig age and accident rate for individual type of accidents. Figure 5 is for ST (structural damage). This type of accident has happened most frequently as shown in Figure 9. Figure 6 is for BL (blowout) and FI(fire). BL and Fl are very closely related and they are 2nd (Fl) and 5th (BL) in number as shown in Figure 9. Figure 7 is for CA(capsize).CA is 4th in number in Figure 9. And Figure 8 is for CL(collision). CL is 9th in number in Figure 9. Types of accident used for Figures 5 through 8 are selected on the bases that they are main types of accident and that they are imagined to be somewhat different from each other in relation to maintenance. ST is imagined to be most closely related to maintenance and collision is least related. It is rather difficult
