In accordance with 46 CFR 139.110, classification societies that are recognized and/or authorized meet the requirements of a TPO.

These classification societies are approved by regulation to perform certain work as a TPO without further Coast Guard approval.

Organizations other than recognized and/or authorized classification societies that conduct TPO functions for towing vessels must be Coast Guard-approved.

An organization seeking approval as a TPO under Subchapter M must, at a minimum, submit an application package containing all the information listed in 46 CFR 139.120. The application package must be submitted to the Towing Vessel National Center of Expertise, which will review the information and determine if the organization meets the minimum standards for approval as a TPO. TPO approvals are granted for a period of five years,

...the USCG informed.

A complete list of all Coast Guard approved TPOs can be found here.