Michael Malinowski and his two friends had been in the stormwater drain for about an hour when they heard a deep rumble that he later described as like an "earthquake".

On January 20 last year, the three graffiti artists, Mr Malinowski, 27, Holly Legge, 21, and Dwaine Larrosa, 25, had gone down the manhole at Lurline Bay to paint a mural, after learning about the site from the urban explorers known as the "Cave Clan".

Michael Malinowski, left, survived, but Holly Legge, top right, and Dwaine Larrosa, whose funeral service was in North Ryde, bottom, died.

It had been a clear day, about 25 degrees on the surface when they descended five floors to do their art, Detective Sergeant Neil Apolony told Glebe Coroner's Court today.

But within a couple of hours the conditions changed dramatically.

