Carbon monoxide killed a supervisor and an engineering draftsman when they entered a lime kiln to check the thickness of the metal walls. The kiln was not blocked off from another nearby kiln which had an induced draft fan in operation. When the two were missed, coworkers put on self-contained breathing equipment and entered the kiln. They found the victims about 160 feet (nearly 50 meters) from the opening. This incident could have been prevented if a blank flange or similar device had blocked the flow of air from the operating kiln to the one being checked.