The Burma Banks are a series of large underwater flat-topped sea-mounts that lie approximately 180 kilometers (100 nautical miles) northwest of the Similan Islands. The banks' surrounding water is over 350 meters deep and large areas rise to within the depth limits of recreational scuba diving.
The name derives from the fact that this 1,500 square kilometre area lies within the exclusive economic zone of Burma. The banks offer some exciting, stimulating diving, but since this is true open-ocean diving, they certainly are not for everyone. These mountains rise very gradually from the depths and are covered with hard coral growth and large patches of sand. Although the huge plate corals (some of these 'plates' could seat all the knights of the round table easily) are in many areas fantastic, that is not the reason for travelling so far out to sea.
The reason is for different types of environments not found in Thailand. And, at the banks, you have a good chance of seeing sharks.
Although not as common as in years past, the chances are better here than in Thailand for sure.  These days, most boats are spending more time in the Mergui Archipelago proper (further inshore) than out at the banks for five reasons.

• First, the diving inshore is so good.

• Second, we tend to see more sharks like gray reef sharks inshore and not here at the banks.

• Third, the currents can get very strong out here, and novice divers have no business being here at all.

• Forth, there is no protection from any kind of weather.

• Fifth, the distances out to the banks are far, and often times not worth it. Your dive master is going to be in the best position to make this decision.

When you see sharks at the banks, the most common type of shark is the nurse shark that grows to over 3 meters in length.
Where else can you go to see nurse sharks freely swimming nose-to-tail over the top of the reef, which have so little fear of divers that they sometimes accidentally swim harmlessly (for both parties) into us?
They are truly the clowns of the banks as it is difficult not to laugh at their frenzied movements. Not enough? How about large silver tip sharks that when attracted by bait swim within range of your Nikons 15 mm lens? If the nurse sharks are the clowns, then the silver tips are the stars.  Reaching an impressive length of two to three meters, these sharks-often compared to the Galapagos shark and easily identified by the white trailing edge on their pelvic, dorsal, and caudal fins-are full-bodied, serious predators.  In addition, you'll see larger reef fish than in other areas of Thailand, such as huge sweet lips and the occasional grouper.  The most common diving technique at the banks are large drift dives over the mountain flats. Currents can be quite tricky here-sometimes changing in direction 90º to 180º very quickly-and very fast.
It is common to drift over one kilometre on certain dives-assuming the current is taking you in the directly you originally planned!
All dive operators that dive at the banks are strict with safety rules. Although these vary slightly from operator to operator, it is roughly agreed that all divers must dive with a 'safety sausage', a whistle or other signaling device, and that either the dingy or the larger vessel should follow the diver's bubbles on the surface.
Finally, it is a must that buddy pairs stay together at all times, and in fact some operators insist that divers dive in a group of at least four.
To become separated from your dive boat this far from land would surely be a disaster.