The answer may surprise you.
Industrial hygienists are often asked if earbuds (in-ear headphones to listen to music) can be used in place of earplugs or ear inserts. The National Institute for Occupational Safety and Health (NIOSH), which tests and approves plugs or inserts for noise attenuation, does not rate earbuds as they are not intended for noise reduction. There are different styles of earbuds that may reduce noise, but only by a few decibels. Noise reduction through the use of earbuds should be considered minimal at best.
Earbuds can have either soft rubber pieces that fit in the ear or a hard plastic earpiece. The length of the earbud can be short or long, and each length will offer a different level of noise reduction. The length of the ear canal in individual workers is also variable. All of these factors can change the amount of noise reduction that can occur. Earbuds are designed for comfort and sound quality, not noise reduction.
When earbuds are used, employee noise exposure consists of the ambient noise plus the sound of the music. This is similar to increasing the volume of a car radio when traveling at high speeds as opposed to when in a quiet neighborhood. The music may make the noisy workplace more pleasant, but the overall sound level is higher. Noise is just unwanted sound.
Some employees wear earmuffs over earbuds to provide noise reduction, but this is not recommended. The combination may prevent the employee from hearing necessary warnings, such as fire alarms, back-up alarms from industrial trucks, or communication or other warnings from adjacent employees or public address systems. If noise is a hazard in the workplace, hearing protection should be used properly.
Bottom line: Do not use earbuds if hazardous noise levels are present, or levels above 85 decibels.