It is good practice to reduce noise levels at the source, or move noise away from workers. However, this is often not a practical option in the aviation maintenance environment. Therefore, hearing protection - like earplugs or ear defenders - should always be used for noise of any duration, above 90 dB. This means that the aviation maintenance engineer will almost always need to use some form of hearing protection when in reasonably close proximity to aircraft whose engines are running. Noise levels can be reduced by up to 20 decibels using earplugs and 40 decibels using earmuffs. However, using ear protection will tend to adversely interfere with verbal communication. Despite this, ear protection must be used consistently and as instructed to be effective.