Fitting, fit testing and wearing hearing protection

A hearing protector is only as good as its fit and the time it is worn. Lesson 8 showed that laboratory ratings overstate real-world protection, mainly because of poor fit. This lesson is about closing that gap: how to fit each type of protector, how individual fit testing measures the protection a worker actually gets, why wearing time matters so much, and how to deal with the practical problems, such as communication, heat, other equipment and comfort, that lead workers to remove protectors.

Fitting foam earplugs

Slow-recovery foam earplugs are the most common protector and the most sensitive to technique. Inserted correctly, deep in the canal, they can give some of the highest attenuation of any protector. Inserted shallowly, with most of the plug sticking out, they may give only a few decibels.

Premoulded plugs must be the right size. Most come in two or three sizes, and many people need a different size in each ear. They are inserted with the same pull-up-and-back technique and should feel snug, with a slight sense of pressure. Custom-moulded plugs are inserted with a twisting motion until they sit fully in the canal; their fit should be verified when they are new and periodically, because ear canals change with age and weight. Banded protectors are pressed into or against the canal entrance; leaving the band resting on clothing or allowing the pods to sit loosely gives very poor attenuation.

Fitting earmuffs

Earmuffs are easier to fit consistently because the user can see and feel the position. The cups must completely enclose the ears, the cushions must seal against the head all the way round, and the headband must provide enough force. The main enemies of an earmuff seal are safety glasses, long hair, hoods and caps, and worn or hardened cushions. Wearing safety glasses with thick temple arms under earmuff cushions can reduce attenuation by several decibels; thin-armed glasses, glasses designed for use with earmuffs, or gel cushions reduce the loss. Cushions and foam liners should be replaced according to the manufacturer's schedule, often every six months with heavy use, or sooner if they are cracked, hard or flattened.

Why individual fit testing matters

Because individuals vary so much, the only way to know how much protection a particular worker gets from a particular protector is to measure it. Field attenuation estimation systems, commonly called hearing protector fit testing, do exactly that. They produce a personal attenuation rating, or PAR, for the worker with the protector fitted as they normally fit it. The PAR replaces the population rating on the package with a measurement for that person.

CSA Z94.2 recognizes the value of fit testing in protector programs, and several provinces' guidance recommends it, especially for workers with high exposures or hearing shifts. It is not yet a general regulatory requirement in Canadian jurisdictions. ANSI/ASA S12.71, published in 2018, sets performance requirements for fit testing systems and is used by Canadian programs too.

Fit testing has value beyond the number. Many workers discover during their first test that they have been inserting their plugs far too shallowly, and the test becomes a training session: the technician coaches the worker, they try again and see their PAR improve. Testing also identifies workers who need a different size or type of protector.

import random, statistics

random.seed(9)
# Personal attenuation ratings (dB) for 40 workers with the same foam plug,
# before and after hands-on training (illustrative).
before = [max(0, round(random.gauss(14, 8))) for _ in range(40)]
after = [min(36, b + max(0, round(random.gauss(9, 4)))) for b in before]

needed = 15   # attenuation needed to bring a 98 dBA exposure to 83 dBA
for label, data in [("before training", before), ("after training", after)]:
    ok = sum(p >= needed for p in data)
    print(f"{label:<16} median PAR {statistics.median(data):4.1f} dB, "
          f"range {min(data)}-{max(data)} dB, adequate {ok}/{len(data)}")

before training  median PAR 13.5 dB, range 0-30 dB, adequate 18/40
after training   median PAR 22.0 dB, range 5-36 dB, adequate 33/40

Before training, many workers in this illustrative group get too little protection from a plug rated far higher. Training improves the median and lifts most workers above the needed attenuation, but a few still fall short and need a different protector. This is the pattern often reported in workplace studies.

Wearing time: the most important factor

Protectors protect only while they are worn. Because the decibel scale is logarithmic and allowable time halves with every 3 dB, even short periods without protection in high noise destroy most of the benefit. The effective protection over a shift depends on the fraction of time the protector is worn:

where A is the attenuation while worn and f is the fraction of noisy time the protector is worn.

import math

def effective(atten_db, fraction_worn):
    return -10 * math.log10(fraction_worn * 10 ** (-atten_db / 10) + (1 - fraction_worn))

shift_min = 480
print("Attenuation while worn: 30 dB")
for removed in [0, 5, 15, 30, 60, 120]:
    f = 1 - removed / shift_min
    print(f"  removed {removed:>3} min of {shift_min}: effective protection {effective(30, f):5.1f} dB")

Attenuation while worn: 30 dB
  removed   0 min of 480: effective protection  30.0 dB
  removed   5 min of 480: effective protection  19.4 dB
  removed  15 min of 480: effective protection  14.9 dB
  removed  30 min of 480: effective protection  12.0 dB
  removed  60 min of 480: effective protection   9.0 dB
  removed 120 min of 480: effective protection   6.0 dB

A protector giving 30 dB while worn delivers only about 20 dB if it is removed for 5 minutes of an 8-hour noisy shift, and about 12 dB if removed for 30 minutes. Removing it for an hour reduces effective protection to about 9 dB. No protector rating, however high, makes up for intermittent wear.

This is why supervisors must insist on protectors being worn for the whole time a worker is in a noise zone, why protectors should be comfortable enough to wear all day, and why practical problems that lead to removal must be solved rather than tolerated.

Why workers remove protectors

Communication and hearing warning signals

Workers often fear that protectors will stop them hearing speech and warnings. In fact, for people with normal hearing, speech in loud noise can be as intelligible or more intelligible with moderate protection, because protectors reduce both the speech and the noise and bring the sound to a level where the ear is not overloaded. The problem arises with over-protection, with workers who already have hearing loss, and with low-level signals. Selection should aim for the 70 to 80 dBA protected range, warning signals should be designed to be audible to protected workers (often 10 to 15 dB above the masked threshold) or supplemented by flashing lights, and workers with hearing loss should have individual assessments.

Workers who must hear radio communications or work near mobile equipment may benefit from communication headsets or level-dependent earmuffs. These devices must themselves be selected so that the sound they deliver to the ear does not add to the worker's noise exposure; some products limit their output to a safe level.

Care, hygiene and replacement

Disposable foam plugs should be used once or for a single shift and discarded if they become dirty, hard or misshapen. Reusable plugs should be washed with mild soap and water, dried and stored in a clean case. Earmuffs should be wiped clean, inspected for cracked cups, worn cushions and loose headbands, and stored where they will not be crushed or distorted. Bending the headband to make it more comfortable reduces clamping force and attenuation. Workers with ear infections, discharge or pain should not use earplugs until cleared by a health professional, and should use earmuffs instead.

Supervising protector use

Supervisors are the key to consistent wear. They can make protectors easy to get by placing dispensers at zone entrances, model correct use themselves, check fit visually during walk-throughs (for foam plugs, only a small part of the plug should be visible from the front), correct poor use promptly and respectfully, and pass worker complaints about comfort or communication to the program coordinator. Many programs use short observations during regular walk-throughs, recording the percentage of workers in a zone wearing protectors correctly, as a leading indicator.