MANILA, Philippines – It’s been almost a month since the explosion at Unit 501B in Two Serendra, a posh enclave in Taguig City.

A week after the May 31 blast that killed 3 and injured 4, Interior Secretary Mar Roxas held a press conference to announce findings that the explosion was caused by a gas leak, and not a bomb.

Three weeks since the announcement however, and as public interest slowly wanes — and with it, liability — the source of the leak still remains a mystery. No official updates since the June 7 press conference have likewise been made.

But facts from the investigation could explain how the explosion happened, or who should be held responsible. Rappler lists them and corresponding questions below.

Fact 1: Residents did not smell anything unusual

Commercialized liquefied petroleum gas (LPG) contains an odorant. The most commonly used chemical additive, mercaptan, is added to LPG to provide a distinctive smell so that in the event of a gas leak, residents are alerted by the foul odor.

Without mercaptan or an odorant, it is virtually impossible to detect gas leaks by smell. The Serendra investigation found that Angelito San Juan, the man renting Unit 501B, did not report any unusual smell when he talked to his friend, Herminia Ochoa, before the explosion, although he did mention feeling suffocated, a symptom of a gas leak.

When Ochoa visited the apartment to see San Juan, she reportedly did not smell any gas from the doorway, and neither did the two guards with her, according to Roxas. Residents from the same building whom Rappler talked to also did not report any unusual odor.

But Roberto Kanapi, Pilipinas Shell vice president for communication, said Shell injects more than the required “chemical additive called ethyl mercaptan in [the gas] we supply.” Pilipinas Shell Petroleum Corp is the gas supplier of Bonifacio Gas Corp (BGC), the exclusive provider of centralized piped-in gas in Bonifacio Global City.

Questions

• Was the gas supplied to Serendra odorless? Is mercaptan really injected to BGC’s gas supply? If Kanapi is to be believed, and the residents did not smell gas, does this mean the mercaptan, by the time it had reached Serendra, had diminished?
• Rappler research shows that mercaptan odorant may fade in rare circumstances. These include times when it sticks to the inside surface of metal storage containers, or is absorbed by the following: the vapor space of used containers, soil, the inside wall of gas pipings, rough wall surfaces, furniture, and fabrics. Could this be what happened, and if so, were the containers or gas pipes used by BGC the culprit?

Fact 2: Burn marks in other units

Roxas said units 506 and 306 had evidence of burn marks, and even a used fire extinguisher. Unit 506 is across the hall and two units away from 501, while unit 306 is one floor below 501.

The same gas pipe provides gas to units 506 and 306. Burn marks and evidence of fire in both units indicate gas continued to flow in those apartments causing the burning, and that the pipe supplying both units was busted.

Question

• Did the pipe break before or after the blast? If the pipe was already broken before the blast, it may be the source of the leak. Gas could have leaked there, but spread down the hall and into 501, hence the explosion. Or did it break from the impact of the blast?

Fact 3: Damage to other units

In a statement released by Ayala Land Inc on the day of the blast, it said 10 units on the 5th floor were damaged by the blast. Ayala spokesperson George Marco said, two apartment units were completely blown out. Others suffered shattered windows, broken doors, and at least one unit on the floor had evidence of burns.

An expert Rappler talked to said it is likely that if the explosion happened inside 501 with the door closed, the extent of damage in the other units would not have been as massive. San Juan’s burns mostly on his back, and his reported plans to leave his apartment just minutes before the blast suggest he was on his way out and his door was open.

Question

• What does the widespread damage on the 5th floor mean? Could it mean there was gas along the corridor, which was also ignited, hence the damage? If so, where did the gas along the corridor come from?

Fact 4: Unit 501 was the source of ignition

The explosion on Unit 501 means it was the source of the ignition. But this does not mean it was also the source of the leak. Gas may have simply entered the unit from the leak’s origin. It is unknown what ignition caused the blast, but in the press conference, geoscientist CP David said it could have come from a mere light switch.

San Juan’s counsel, Raymund Fortun, told Rappler his client did not cook while he was at the apartment, as there are no utensils in the unit.

Questions

• With San Juan still intubated owing to injuries from the blast and without his testimony, investigators have yet to determine the source of the ignition. Was it a light switch? A match? From the information at hand, however, Roxas said investigators have concluded San Juan’s behavior was “normal.”
• And if the leak did not come from Unit 501, then how did the gas enter the apartment? If the unit’s gas was unused, as Fortun says, could the gas have then seeped through the door and not through the pipes?

Fact 5: No alarm went off

No gas detector sounded before the explosion, despite there having been gas present. Residents Rappler talked to said their gas detectors are extremely sensitive that, they are set off even by detergent or insect repellant. They said the sound is so loud it can be heard from outside the unit. But not a single alarm was reported to have gone off on the 5th floor.

Questions

• Were the gas detectors on the 5th floor not working? Or were none of them plugged, which is the residents’ responsibility? If the gas detectors were not working, why not?
• A One Serendra resident told Rappler a Serendra inspection of her gas detector showed it was defective, as it did not detect gas sprayed onto it. How many gas detectors in Serendra are defective and why were they not monitored? – Rappler.com