He has not left his apartment since out of fear and does not know what has happened to his work, which he thinks has been destroyed.
"That's nothing compared to the lives lost. There's still a sense of bewilderment here."
Mr Clapshaw, who lives about 100m away from the site, had been in the area earlier on Monday evening and had been at the intersection about three minutes before the explosion.
"I'd just driven past. I stopped to talk to a friend and then heard the blast. I thought it was lightning."
Volunteer paramedic Marko Cunningham, of Wellington, was among the first medical aid to arrive on the scene.
"There were bodies everywhere - some were shredded," he told Radio NZ. "There were legs where heads were supposed to be. It was horrific."
A group of Kiwi Muai Thai kickboxers in Bangkok for a tournament have been confirmed safe.
Vaimoana Tapaleao