Last month's fire at a SingTel's Bukit Panjang Internet exchange which crippled critical services across Singapore was caused by an employee who did not follow strict maintenance procedures, including the use of an unauthorised blowtorch.
SingTel said this in a statement on Wednesday adding that it had completed preliminary investigations into the Oct 9 incident which occured during maintenance work at one of the lead-in pipes located in the cable chamber.
The fire, which took down banking, payment and Internet services, was localised in one of three pipes that houses cables connecting to customer homes and business premises.
The blaze damaged 149 fibre optic cables, two-thirds of which belong to national fibre broadband network builder OpenNet.
As a result, services of operators like StarHub and M1, which buy wholesale fibre links from OpenNet, were also disrupted.
During the incident, SingTel said it immediately activated contingency and diversification plans, including re-routing traffic through other exchanges to minimise disruption to the majority of its customers.
In the statement, the telco said it treats the incident "very seriously" and has always ensured that its contingency plans and safety measures meet global benchmarks.
The telco said it has since strengthened existing processes and measures to prevent a recurrence of similar incidents.
The measures include limiting maintenance work which requires heat to be applied and reinforcing training on safety requirements and operations.
An independent review by the SingTel Board Committee of Inquiry (BCOI) is on-going. The BCOI reports to the Board of SingTel.
The BCOI is responsible for investigating the facts and circumstances leading to the fire, reviewing and recommending improvements into the company's incident management, network design and contingency processes.
Ms Chua Sock Koong, SingTel group CEO, said: "We recognise the importance of reliable communication services to customers and Singapore's status as a leading financial and business hub.
"We apologise unreservedly to all our customers for any inconvenience caused. We are committed to learning from this experience and welcome recommendations from the BCOI and independent experts to enhance our operations."
SingTel added it will make the BCOI findings and recommendations public in the interest of transparency.