But that means that a person would be killed even if they are miles away? Maybe tens of miles.

Found it: Based on sonar guidelines and studies on sound propagation, a diver exposed to 235 dB low-frequency sonar would likely need to be more than 1.5–2 kilometers (1–1.2 miles) away to ensure safety.

However, pings are conical and the strongest sonar is at the bow. So you could literally be safe if you were diving behind it.