An innovative active noise control earplug for the protection of first aid ambulance drivers

Introduction
The drivers of ambulances of emergency service 118 are exposed to noise generated primarily by the siren. Measurements in some Italian provinces indicate the possibility for drivers to exceed the lower action value of 80 dB (A) of the daily noise exposure LEX established by the Legislative Decree 81/2008 (European Union noise Directive 2003/10/EC).

Methods
We have developed a prototype of a special active noise control earplug device, based on two-channel system ATH311 developed by Active Ltd, which can track the fundamental frequencies generated by the siren of an ambulance and drop them in real time in the driver’s ear canal. The system was tested in the acoustics laboratory of the Department of Occupational Hygiene of INAIL (formerly ISPESL), via the use of a B&K 4128 dummy head and torso simulator (HATS) and a test ambulance.

Results
The Active Insertion Loss, the difference between the sound level in the ear canal with the ANC system OFF and ON, was greater than 10 dB in both ears of the dummy during the normal operation of the siren of the ambulance with the engine off and windows closed, bringing the perceived noise level well below the lower action of 80 dB (A) set by noise Directive 2003/10/EC.

Discussion
The trial results showed an excellent capacity of the active control earplug to reduce the sound levels generated by the siren of an ambulance, without interfering with other signals (spoken voice, radio) during the course of the service required. Given the flexibility of the system ATH311, it is expected to extend the device to drivers of other public safety services and emergency services (police, fire, ...). The company ARES 118 of the Lazio region that manages public service emergency department is ready to adopt the device as soon as it will be engineered.