The Taiwan Transportation Safety Board published the final investigation report of TRA Train No. 2721 occurrence at Zhuoshui Station.

At 1610 on June 1, 2020, Train number 2721, Local Train of Taiwan Railways Administration, MOTC (TRA) ran between Yuanquan Station and Zhuoshui Station (Jiji Line). Due to lubricating oil leaking from the joint between oil returning pipe and turbocharger on the underframe of the first car (No. DR1012), the driver noticed the Oil Pressure indicator was off and stopped the train immediately. The fire was burning out from the bottom of the first compartment (on the hood of the turbocharger) and was put out by the driver with a dry powder fire extinguisher. The Train Master evacuated the passengers onboard and reported to Zhuoshui Station. There were no fatalities or injuries in this occurrence.

In accordance with the Transportation Occurrences Investigation Act, R.O.C., and the definition of major transportation occurrences specified therein, the Taiwan Transportation Safety Board is the independent agency in charge of investigating the railway accident. The agencies (institutions) invited to participate in the investigation includes the Taiwan Railways Administration (TRA) and Railway Bureau, MOTC.

Findings

This investigation report summarizes three categories of investigation findings on the basis of factual information and comprehensive analyses collected during the investigation period: findings related to probable causes, findings related to risk, and other findings.

Findings related to probable causes

1. During the train operation between trip No. 2716B and No. 2721, the outer bolt at the joint between the oil returning pipe and turbocharger on the trainset was loosed and lost. The lubricating oil leaked from the joint, adhered to the inner heat shield of the turbocharger, and caused the fire when over-temperature. The temperature of the inner layer could reach 364°C and surpass the fire point 266°C of the lubricating oil according to the measurement on-site.
2. The loose bolt may be caused by inadequate maintenance, without following the pre-fastening method and torque value required from the maintenance manual suggested by the manufacturer during the latest Level 3 Maintenance Process. Additionally, the bolt tightening checking process has not been clearly defined within Level 1 Maintenance and the loose condition of the bolt could not be noticed in time before the occurrence happens.

Findings related to risk

1. The TRA does not fully comply with the requirement according to the maintenance manual suggested by the manufacturer and failed to require the maintenance staff to fasten the bolt between the joint of the oil returning pipe and turbocharger with the suggested torque value to ensure the required fastening of the bolt of trainset DR1000.
2. The TRA has adopted the non-original manufacturer spare part for the bolt with removable washer when performing the maintenance job to the oil returning pipe and the turbocharger of trainset DR1000. It is possible that the loosen bolt was caused by failing to apply the washer.
3. The TRA maintenance staff evaluates the adequate fastening of the bolts mainly by knocking on the bolts during the Level 1 and 2 Maintenance, and it is not an ideal method for determining the loosened bolt.
4. The TRA failed to clearly define the troubleshooting procedures and the conditions to restart the engine under low lubricating oil pressure conditions on trainset DR1000. In this occurrence, the driver pushed the reset button to restart the engine without confirming the lubricating oil volume and pressure level. This might cause damage to the engine and affect operational safety.
5. The contents of inspection item lists, inspection records, and inspection procedures for Level 1 to 4 Maintenance are not consistent, the practical work could not be performed properly by following the standard operational procedures.
6. The TRA failed to define the job responsibilities and function clearly for the supervisor, inspector, and technical assistant in the depot and main workshop for Level 1 to 4 Maintenance, and this might cause difficulty to manage and ensure the maintenance quality.

Other Findings

1. The firefighting process performed by the Train Master and Station Master in the occurrence is consistent with the relevant procedures of TRA.
2. In the current inspection records for Level 1 to 4 Maintenance of TRA, only the name of the devices and inspection items are provided, together with a simple checkbox for marking, but the implementation procedures and qualification criteria are not specified for each inspection item.
3. In the current Level 4 Maintenance inspection records of TRA, the adopted gap allowance standards for assembling the turbocharger parts are not consistent with those suggested in the manufacturer's maintenance manual.

Safety Recommendations

To TRA

1. Enhance the inspection procedures for trainset DR1000, especially the necessity of the bolts which must be fastened by using a torque wrench for the key facilities, marking the fastened position, and the relevant confirmation procedures during the maintenance for ensuring the bolt fastening performance.
2. Introduce the proper checking and verification procedures before adopting non-original manufacturer spare parts for the bolt and enhance the procedures to ensure the bolt fastening with the washer for eliminating the risk of a loosen bolt.
3. Amend the current work contents, inspection methods, used tools, and pass-fail criteria defined in the Level 1 to 4 Maintenance documents of trainset DR1000 by referring to the manufactured maintenance manual in order to attain the maintenance quality suggested by the manufacturer.
4. Clearly define the job responsibilities and functions for the supervisor, inspector, and technical assistant in the depot and main workshop in each maintenance level to ensure the quality of maintenance and supervision.
5. Clearly define the trainset DR1000 Driver’s troubleshooting procedures under low lubricating oil condition/pressure to ensure the work could be done properly.

Full Final Report in Chinese is available for download at https://www.ttsb.gov.tw

Vivi Yang, Secretariat Office
Tel: +886-2-7727-6217
E-mail: viviy2314@ttsb.gov.tw