In the first hours after the attack, most of the thousands of rescuers and workers rushed into the clouds of dust and smoke without much regard for their lungs, the reports say, based on surveys of the workers.
Among those who had severe cases of a cough, 93 percent said they used respirators "rarely or not at all" on the first day and only a little more in subsequent days.
Reviews of the emergency response concluded that this was partly the result of the urgency of the job and also because New York City officials and federal officials simply did not have the right gear on hand.
A week passed before most workers were wearing the device that federal worker-health officials decided was best suited to the conditions: a half-face respirator, a rubbery mask that seals around the nose and mouth and can be fitted with different filters.
During their first hours at the site, firefighters often had inappropriate protection. Most either had no lung protection or used paper masks. Others relied on self-contained breathing apparatus used to fight conventional fires. But these SCBAs provided air for only about 8 to 15 minutes.