A combination of factors including the outdated use of lead sealants as well as a blowtorch with a overly hot flame likely caused a fire which damaged a SingTel Internet exchange in October.

SingTel's Board Committee of Inquiry, which comprised three independent members of the company's board, presented its findings at a briefing on Monday evening.

The findings showed that the fire in an underground cable chamber at the Bukit Panjang exchange on Oct 9 was started when an employee used an unauthorised blowtorch to heat one of the lead seals that keep water and gas out of the chamber at the points where cables exit. The committee learnt that the employee, who was a 30-year veteran with the company, had forgotten to bring the required blowtorch which produced a 450-degree flame and instead borrowed another from a contractor, which had a flame twice as hot.

The lead-based sealant and polyethylene plastic sheaths on the cables overheated and began to smoulder undetected.

When the worker left for lunch afterwards, he neglected to turn on the smoke detector, which had been turned off during the work.

The committee's report called the use of lead sealants a fire risk, and the use of such hot works in cable chambers "outdated, unnecessary and hazardous".

The fire took down banking, payment and Internet services in many parts of Singapore for more than 24 hours.

SingTel chairman Simon Israel said the company's management has accepted all of the committee's findings and recommendations. These include switching to lead-seal alternatives that do not require hot works by the end of 2014, as well as switching to flame-retardant PVC instead of polyethylene, and working with the telecoms industry to collaborate on disaster recovery, among others.