We strongly recommend that you have travel insurance that includes coverage for SCUBA diving. Or separate travel and diving insurance.
Why diving insurance?
Diving related accidents are rare but when they happen they can be serious. Phuket has three hyperbaric chambers and the dive boats all carry emergency oxygen. The evacuation procedure from boat to hospital is very efficient. But recompression chambers are expensive.
A typical US Navy Table 6 treatment in a Phuket hyperbaric chamber costs about US$ 4,000, and you may need multiple treatments. That’s not including all the associated costs of hospital care, medication, transport and so on.
Most Thailand dive boats cover divers for these costs on their insurance policies but these policies require you to pay first and claim back later. They also do not cover repatriation to your home country or follow care in your home country. So it’s preferable to have your own insurance that will get you treatment quickly and repatriate you if required.