The regulatory body was investigating the disaster on 9 December which killed 22 people, many of them tourists and their guides, out of 47 people visiting White Island in New Zealand.
The eruption on the White Island Volcano, also called Whakaari, was investigated by WorkSafe, which regulates workplace-related incidents in New Zealand. It imposed the maximum fine of NZ$1.5m (£790,000) on 10 parties and three individuals were charged with a maximum fine of NZ$300,000 (£160,000).
Issuing a statement on Monday, WorkSafe said the 10 organisations and three individuals had failed to meet their health and safety obligations while taking tourists to the active volcano.
"This was an unexpected event, but that does not mean it was unforeseeable and there is a duty on operators to protect those in their care," said Phil Parkes, chief executive of WorkSafe.
The active volcano, which has been erupting since 2011, was visited by thousands of tourists before the eruption. None have visited since the fatal incident last year.
GeoNet, the volcano monitoring service of New Zealand, raised the alert level to "moderate to heightened volcanic unrest" at Level 2 out of 5 just weeks before the disaster.
Mr Parkes described the investigation as the "most extensive and complex" in the history of WorkSafe.
“Those who went to the island did so with the reasonable expectation that there were appropriate systems in place to ensure they made it home healthy and safe,” Mr Parkes said.
The WorkSafe investigation did not focus on rescue and recovery of the dead and injured people, which means there would be no charges related to post-disaster work.
The 22 victims on the island were mostly from Australia as well as others from New Zealand, Germany, China, Britain and Malaysia.