A plumber was killed and his associate injured in a freak accident that saw a residential septic tank explode in Cakung, East Jakarta on Monday.

According to the police, the victims were hired by the homeowner, named Agus Sholeh, to extract waste from the septic tank, which was buried underneath his house, using an industrial vacuum. In order to convince Agus that all the waste had been sucked up, one of the victims lit up a newspaper on fire and tossed it inside the septic tank.

Convinced, Agus then went out to withdraw money to pay the plumbers. While the plumbers were waiting for his return, this happened:

Based on their preliminary investigation, police say that the fire is believed to have triggered the explosion.

“The gas that had accumulated in the septic tank for decades was exposed to fire,” Cakung Police Crime Investigation Unit Head Tomi Sirait told reporters yesterday.

One of the plumbers was killed from injuries he sustained when he fell into the hole that opened up in the explosion. His associate reportedly suffered minor injuries.

“It was a workplace accident. The plumber caused it, and he was the victim,” Tomi added.

In light of the incident, the Indonesian Institute of Sciences (LIPI) warned that gas build up in septic tanks could pose a serious threat to anyone.

“By scientific logic, inside septic tanks there is methane gas that is highly flammable. The incident in Cakung is very likely to be the result of a clogged gas output pipe or the lack of such an outlet [for the gas],” LIPI researcher Neni Sintawardani told CNN Indonesia.

Neni added that methane in septic tanks, which is the byproduct of micro organic reactions in human waste, is generally harmless in small quantities, so homeowners should ensure that their septic tanks have an outlet for the gas to escape.

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