THE human factor was behind the infamous incidents in Chernobyl in the former Soviet Union and the Three Mile Island in the US.

"It may be wise to remember that explosions could very easily occur if an engineer does not exercise due care and diligence.

"When an engineer carries out tests in a power station, there are a few sequence of procedures that he has to strictly adhere to," said A. Ramanath, NEB/TNB's former deputy general manager (Planning and Construction Division).

Investigations into the Chernobyl disaster of April 26, 1986, showed that the engineers in charge of conducting the safety test had failed to follow the established rules and follow the prescribed procedures.

A day before the accident, one of the reactors was scheduled to be shut down for maintenance as it was nearing the end of its first fuel cycle. An experiment was proposed to test a safety emergency core cooling feature during the shutdown procedure.
But due to a whole sequence of events caused by human errors, the valves in the system leading the water to the reactor which should have been left open were shut and those which were required to be shut were opened, resulting in increased pressure within the reactor vessel.

In the Three Mile Island Power Station explosion on March 28, 1979, test engineers had failed to follow the prescribed operating and test procedures.

"The reactor pressure relief valve had operated when the wrong valve was closed during a safety test," said Ramanath.