NEW YORK (Reuters) – Three firms that bought crude oil last year from U.S. emergency stockpiles raised concerns about dangerous levels of a poisonous chemical in the cargoes, according to internal Energy Department emails and shipping documents reviewed by Reuters. FILE PHOTO: An oil storage tank and crude oil pipeline equipment is seen during a tour by the Department of Energy at the Strategic Petroleum Reserve in Freeport, Texas, U.S., June 9, 2016. REUTERS/Richard Carson/File Photo Problems with crude quality would make the U.S. Strategic Petroleum Reserve (SPR) less useful in an emergency because refiners would need to spend time and money removing contamination before producing fuel. The reserve is the world’s largest government stockpile, currently holding 665 million barrels. Hydrogen sulfide (H2S) occurs naturally in crude and natural gas, but oil producers typically decontaminate such products before delivery to buyers. High levels of H2S can corrode refinery parts […]