"Do not scrub or scratch the skin", Guam authorities advise, adding that the hair should be washed with shampoo or soap, while conditioner should not be used as it would bind radioactive material to the hair.
The small USA territory of Guam has become a focal point after North Korea's army threatened to use ballistic missiles to create an "enveloping fire" around the island.
The guidance includes taking cover quickly in a concrete structure, preferably underground.
President Trump assured Mr Calvo that Guam is safe during a phone call.
Trump on North Korea - Military solutions are locked in place. "I'm working with Homeland Security, the rear admiral and the United States to ensure our safety, and I want to reassure the people of Guam that now there is no threat to our island or the Marianas". Guam officials are disseminating fact sheets to help residents prepare for a possible missile attack from North Korea. The chilling two-page fact sheet details what citizens of the 162,000-populated island that houses 6,000 USA troops should do to survive the worst outcome of the boiling tensions between Washington and Pyongyang.More news: Anthony Scaramucci says White House 'plotters' are working to oust Donald Trump
More news: Google Fire Software Engineer Over Offensive Memo
More news: Global Stocks Selloff Stops at Wall Street; Gold, Yen Tick Up
Officials have not raised the USA territory's threat level after Pyongyang said it had laid out plans to strike near the island in the coming weeks.
Guam's Office of Civil Defense began disseminating fact sheets Friday to help residents prepare for a North Korea missile attack.
The island houses about 7,000 USA troops spread between Andersen Air Force base and Naval Base Guam.
Still, Dee Cruz, a senior watch officer with Guam Homeland Security, concedes that "folks here are concerned because there's a lot of talk about it" - alluding to extensive media coverage of the public statements made by Trump and his counterpart in North Korea, Kim Jong Un. Lying flat on the ground while covering your head would also be a sensible decision if caught outside, the document reads, as "it could take 30 seconds or more for the blast wave to hit".