The US Centers for Disease Control (CDC) National Institute for Occupational Safety and Health (NIOSH) regulates respirators (N95 masks) for occupational health. NIOSH maintains an extensive list of approved N95 respirators. These NIOSH-rated respirators are intended for industrial use, but are appropriate for healthcare use under the emergency circumstances brought on by the COVID-19 pandemic, hence these respirators will not be found on the FDA Establishment Registration & Device Listing database.
FDA 510(k) Cleared
The US Food and Drug Administration (FDA) requires manufacturers of certain classes of products to submit a technical dossier to demonstrate that the device is "substantially equivalent" to a predicate device (i.e. a product already cleared for sale in the US). The FDA reviews the 510(k) submission and "clears" the specific device. Certain classes of medical devices require such clearance before they can be legally distributed in the United States. Products on the supplier list with a regulatory status of FDA 510(k) Cleared are listed in the FDA Premarket notification database.
CDC NIOSH/FDA Memorandum of Understanding (MOU) for N95 respirators
The FDA last cleared an N95 respirator in April, 2018. From this point forward, there is an agreement that N95 respirators will not require 510(k) clearance from FDA but rather will be certified by NIOSH. This MOU does not apply to surgical masks which are still regulated as surgical and infection control devices; Class II medical devices within product category FXX.
FDA EUA List
During the COVID-19 crisis, the FDA issued Emergency Use Authorizations (EUAs) that waived certain regulatory requirements and specifically authorized the importation and distribution of specific items listed in the EUA for the uses described in the EUA, so long as the importation, distribution or use of such items fell within the scope of authorization in the EUA. On June 30, 2021 the FDA removed a number of products from the EUA list, including KN95 masks as well as decontamination and bioburden reduction systems to disinfect disposable respirators. This action was taken in response to an increase in domestically-manufactured NIOSH-approved N95s available throughout the country. You can read the full announcement from the FDA here
While the FDA has revoked its EUA for KN95 masks, it does not mean that these respirators are not adequate for consumer use, only that they are no longer appropriate for healthcare workers given the abundant supply of N95 respirators.