While many people measure snorkeling skills by how deep they can freedive or how long they can stay beneath the surface, the real measure of skill is the ability to remain relaxed.
Deep snorkeling results in overpressure in our lungs. The pressure underwater goes up about 1 atm for every 10 m deeper that you go. But as long as you don't try to exhale you are completely safe. Knowing your limits and not exceeding those limits is excellent advice for people engaged in snorkeling.
Limit the depth of your snorkeling adventure to the length of the snorkel (tube) and your breathing capacity.
Diving and Snorkeling in Palawan, Philippines. Eastern Caribbean Cruises. British Virgin Islands (Tortola) Best Sites or Areas: Norman, Peter and Salt Islands. The Indians sites, near Norman Island, are excellent both for snorkeling and diving, having areas as deep as 60 feet or as shallow as five. It is really deep snorkeling at Black Rock.