 Excessive noise can cause hearing loss in marshallers, either imperceptibly over years or after a one-time acoustic trauma.In the United States noise limits at work are set by the Occupational Safety and Health Administration (OSHA).Aircraft signals vary slightly among the North Atlantic Treaty Organization (NATO) Standardization Agreement 3117, Air Standardization Coordinating Committee Air Standard 44/42A, the Appendix 1 of the Annex 2 to the Chicago Convention on International Civil Aviation, and Federal Aviation Administration (FAA) signals.