Who is responsible for approving respirators (like N95s) for occupational use?

NIOSH (National Institute for Occupational Safety and Health, part of the CDC) is the federal agency responsible for testing and approving all respirators used in U.S. workplaces. OSHA's respiratory protection standard then requires that, when respirators are needed, only NIOSH-approved respirators be used — but OSHA itself does not do the approval testing. The FDA has a narrower, separate role regarding certain surgical N95s intended for specific medical claims, and the EPA is unrelated to respirator approval.