SINGAPORE - The double deaths were not just rare, they should not have happened at all.
Mr Song Shing Hae, president of the Singapore Underwater Federation, the national sports authority for diving and underwater activities, said this emphatically.
"Unforeseeable circumstances can catch even the most experienced instructors by surprise. But it is important to mitigate all possible incidents."
Although investigations are still underway, dive experts give The New Paper some possible scenarios.
1 Lack of air
The Tioman dive shop operator, Mr Reynolds Esteva, claimed that checks after the accident revealed that Dr Lee Yong Yeow's tank, had run out of air while instructor Tan Seah Heng had 30 bars of air left, reported Shin Min Daily News on Monday.
Divers would usually start their dive with 200 bars of air and resurface when there is 50 bars of air left.
Instructors would also not risk allowing a student to dive without a full tank during training, said Mr Song, who has more than 30 years of diving and instructing experience.
In a situation where a diver runs out of air, another will share air with their buddy via an extra hose, also known as the octopus. Divers are also supposed to check the amount of air that is left in their tank every 5 to 10 minutes, said the experts.
"You will realise when your tank is running low because you will find it difficult to breathe," said Mr Welson Tesorio, 31, a diving instructor at Waikiki Dive Centre. He has been diving for eight years.
The most common trigger for a diving incident is lack of air. If the diver is caught unaware, lack of air will result in a loss of consciousness in less than five minutes, and even less if the diver panics, said Dr Soh Chai Rick, director at the Hyberbaric & Diving Medicine Centre at the Singapore General Hospital.
2 Lack of experience
The experts also pointed out that the first diving experience can be overwhelming and it is important for a new diver to feel comfortable in such a situation.
Mr Leon Boey, 34, who owns diving operator Living Seas and has seven years of instructor experience, said: "For a firsttimer, they could get stressed over small problems with their masks or regulators.
There will be warning signs like erratic movements.
"It is the instructor's duty to address these problems before the student does something drastic like tearing off their mask, trying to resurface, or grabbing at anyone or anything."
Emergency ascent is the most common dangerous behaviour in an incident, said Dr Soh. This happens when a diver tries to resurface suddenly, and arterial gas embolism takes place.
This means that bubbles will be formed in the bloodstream, explained Dr Soh. This takes place in a matter of seconds.
3 Lack of proper equipment and procedures
Faulty equipment would have been picked up during the usual vigorous checks before a dive, said the experts.
Mr Esteva also told Chinese newspaper Shin Min that checks on the tank after the accident revealed that the equipment was not faulty.
A diving instructor, who wanted to be known only as Mr Tan and who has four years of experience, said: "It is possible for one person to have a faulty tank, but for two people's equipment to be faulty at the same time is rare."
In January, the Singapore Standards Council and the National Water Safety Council introduced a guide that outlines the roles and responsibilities and safety requirements for divers and operators.
A new certification scheme, DiveSafer, to accredit operators and instructors based on the new guidelines, was launched in April. But the take-up rate has not been too encouraging, said Mr Song.
So far, only eight operators and 13 instructors have signed up, according to its website.
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