In February 2021, a damaged recoil spring assembly for an excavator had been removed from the track arrangement and stored outside a heavy mobile plant workshop. The following morning, a fragment of the spring separated while under compression and travelled approximately 28 metres across the yard and through a workshop wall, coming to rest in a walkway beside a workbench.
The fragment, weighing 9 kilograms, penetrated the shed wall at approximately 6.5 metres above floor level. While employees located at the opposite end of the workshop heard a loud bang when the spring fragment impacted the wall, no persons were present in the areas where the fragment came to rest or outside where the spring was being stored.
Contributory causes
- The recoil spring assembly is designed to be installed and removed as a pre-assembled unit with the spring compressed/pre-loaded by approximately 58,000 kilograms of force.
- No information was provided by the original equipment manufacturer (OEM) on the potential hazards associated with performing work on the track recoil assembly with a damaged spring.
- Prior to removal, the recoil spring was inspected via the inspection window on the side track frame, which identified sections of the spring were cracked and missing.
- Although the spring had cracks and segments missing, the assembly remained under compression/load after it had been removed from the excavator, despite the integrity being compromised and susceptible to failure while under load.