Dr Campbell Murn, a previous member of the government's zoo expert committee and lecturer at the University of Reading, said while it was a tragic incident, determined people could get inside zoo enclosures.
"I view it in the same way a determined thief will get into somebody's house or somebody's car and despite the best security systems and enclosures sometimes these things happen," he said.
"One of the fundamental approaches of a modern zoo is to give people a wildlife experience and keep them safe so they can learn and they can enjoy being near the animals, but keeping a safety distance that is relevant but not making it too heavy handed."
Speaking on BBC Radio 4's Today programme, Murn said public safety was an "enormous consideration" for zoo standards in the UK.
A spokesperson for the Born Free Foundation, which campaigns to phase out zoos, called for an "urgent review" into "how the man managed to enter the enclosure and what happened next".
Born Free's co-founder Will Travers said: "Putting dangerous wild animals on public display in zoos and safari parks creates a false relationship with humans.
"Visitors are encouraged to get up close and personal - that is a deeply unnatural situation and not without risk."