Double hearing protection: combining earplugs and earmuffs

When a combination comes into question

At very high sound pressure levels a single hearing protector may not be enough. According to section 4.4 of DGUV Rule 112-194, a tested combination of earplugs or custom-moulded earplugs with earmuffs then comes into question. The order of measures applies first: reduce noise at the source before combining hearing protection.

Conditions for earplugs and earmuffs

• Earplugs: in principle all earplugs are suitable except banded earplugs.
• Stem and handle: with flanged earplugs and custom-moulded earplugs, the stem or handle must not touch the inside of the earmuff, otherwise the fit can change, pressure points can occur or rubbing noises can arise.
• Earmuffs: models with headband or for helmet mounting are possible, as are noise-protection helmets.
• Fit: the earplugs must not slip when the earmuffs are put on (section 7.9.1). So insert the earplugs first and check the fit, then put on the earmuffs (How to insert earplugs correctly).

What the combination achieves

The attenuation values of the two protectors cannot simply be added: adding M 35 dB of a foam earplug and M 28 dB of an earmuff would give 63 dB. For tested combinations the rule instead gives values of up to about M = 40 dB in the mid-frequency range (section 7.9.1). That is a guide value from the rule, not the attenuation of a particular pair of products.

Real-world deduction for combinations

For calculating the residual level, annex 1 of the rule applies a real-world deduction of 9 dB or 5 dB for combinations of earplugs and earmuffs, depending on the type of earplug: 9 dB for earplugs that are shaped before use, 5 dB for pre-moulded ones. With qualified use the deduction does not apply (Qualified use).

Example from the rule: blasting

Annex 1 works through a case of CO₂ blasting: the continuous level is about 124 dB(A) over eight hours and the noise class is M. For 85 dB(A) at the ear, M = 124 − 85 + Ks is required.

No single hearing protector reaches 44 or 48 dB. As solutions the rule names the combination of earplugs and earmuffs, if possible under the blasting hood, taking the hood attenuation of about 5 dB into account, and qualified use with training. With a hood and qualified use, hearing protectors with M ≥ 34 dB are enough.

From 110 dB(A): special training

At a daily noise exposure level of 110 dB(A) and above, section 7.9.1 makes special training mandatory, so-called qualified use. It comprises practical exercises at least four times a year and a check of the protection actually achieved by the individual.

Communication in very high noise

Where communication is needed despite the high level, hearing protectors with safety-relevant communication come into question; they transmit by radio (for example Bluetooth, DECT or PMR 446) or cable (section 4.6.2). Warning signals must be checked with the complete equipment (hearing warning signals).