Capstone: a hearing conservation program

This capstone brings the whole course together. You will work through the design of a hearing conservation program for an invented company, Larkspur Metal Works, using the methods from earlier lessons: assessing exposures, ranking sources, choosing engineering and administrative controls, selecting protectors, planning training and audiometric testing, and setting up evaluation. Larkspur is fictional, and its noise levels, costs and staffing are illustrative, but the problems it faces are typical of real plants. At the end, you will review a weak draft program and identify what it is missing.

The plant

Larkspur Metal Works is a 95-person metal fabrication plant in Ohio. It makes steel enclosures and brackets for the electrical industry on two 8-hour shifts and one 10-hour weekend maintenance shift. The plant has a stamping area with four mechanical presses, a fabrication bay with shears, grinders and welding stations, a paint line with a compressed-air blow-off station, an assembly and packing area, a maintenance shop and offices. It is covered by federal OSHA and 29 CFR 1910.95, and it has a labor-management safety committee.

Until now, Larkspur's noise management has consisted of earplug dispensers at the doors of the stamping area and a sign reading hearing protection required. There has never been a full noise assessment, and audiometric testing was dropped five years ago after a change of provider. Two long-serving press operators have recently filed hearing loss claims, and the new health and safety coordinator has been asked to build a proper program.

Step 1: assess exposures

The coordinator hires an occupational hygienist, who runs a noise survey with area measurements, full-shift dosimetry on at least three workers in each job group over several days, and task-based measurements for the main tasks. The table summarizes the task data for five similar exposure groups.

import math

def lex8(tasks):
    """tasks: list of (hours, dBA). Lex,8 normalized to 8 hours."""
    return 10 * math.log10(sum(h * 10 ** (L / 10) for h, L in tasks) / 8)

groups = {
    "Press operators":   (12, [(6, 98), (1, 90), (1, 70)]),
    "Fabricators":       (18, [(1.5, 102), (2, 94), (3.5, 86), (1, 70)]),
    "Paint line":        (8,  [(2, 99), (5, 84), (1, 70)]),
    "Assembly/packing":  (30, [(7, 83), (1, 70)]),
    "Maintenance (10 h)": (7, [(4, 96), (4, 88), (2, 80)]),
}
over = 0
for name, (n, tasks) in groups.items():
    L = lex8(tasks)
    dose = 100 * 10 ** ((L - 85) / 10)
    flag = "over 85" if L > 85 else ("within 3 dB" if L > 82 else "")
    if L > 85:
        over += n
    print(f"{name:<19} workers {n:>2}  Lex,8 {L:5.1f} dBA  dose {dose:6.0f} %  {flag}")
print(f"Workers over 85 dBA Lex,8: {over} of {sum(n for n, _ in groups.values())}")

Press operators     workers 12  Lex,8  96.9 dBA  dose   1536 %  over 85
Fabricators         workers 18  Lex,8  95.8 dBA  dose   1194 %  over 85
Paint line          workers  8  Lex,8  93.3 dBA  dose    678 %  over 85
Assembly/packing    workers 30  Lex,8  82.5 dBA  dose     56 %  within 3 dB
Maintenance (10 h)  workers  7  Lex,8  93.7 dBA  dose    737 %  over 85
Workers over 85 dBA Lex,8: 45 of 75

Four of the five groups are over an 85 dBA exposure, the OSHA action level and the NIOSH limit, so they must be in the hearing conservation program. Using OSHA's 5 dB rule, the press operators, fabricators and maintenance mechanics are also over the 90 dBA PEL, which triggers the requirement for feasible engineering or administrative controls. Assembly and packing is within 3 dB of 85 dBA, so the coordinator decides to include that group too, as a precaution.

Step 2: rank the sources and plan engineering controls

The hygienist's source measurements and switch-off tests identify the main contributors in each area. The coordinator and the maintenance manager estimate the reduction and cost of possible controls, and rank them by the exposure reduction they buy and the number of workers who benefit.

The plan puts the cheap, high-value measures first: air nozzles, lined chutes and bins, and exhaust silencers in the first three months, followed by the grinding improvements and ceiling baffles in the first year, and the press enclosures in the second year as part of the capital budget. The coordinator documents why the press enclosures cannot be done immediately, including cost and the need to redesign material handling, and sets a review date. Buy-quiet requirements are added to all purchase specifications, with a target of 80 dBA at the operator position.

import math

def lex8(tasks):
    return 10 * math.log10(sum(h * 10 ** (L / 10) for h, L in tasks) / 8)

before = {
    "Press operators": [(6, 98), (1, 90), (1, 70)],
    "Fabricators": [(1.5, 102), (2, 94), (3.5, 86), (1, 70)],
    "Paint line": [(2, 99), (5, 84), (1, 70)],
}
# Phase 1 (nozzles, lined chutes, silencers) and phase 2 (grinding, baffles, enclosures)
phase1 = {
    "Press operators": [(6, 98 - 6.2), (1, 90), (1, 70)],     # chutes 5 dB plus silencers 3 dB combined
    "Fabricators": [(1.5, 102), (2, 94), (3.5, 86), (1, 70)],
    "Paint line": [(2, 89), (5, 84), (1, 70)],
}
phase2 = {
    "Press operators": [(6, 98 - 6.2 - 7), (1, 90 - 3), (1, 70)],
    "Fabricators": [(1.5, 102 - 6), (2, 94 - 3), (3.5, 86 - 3), (1, 70)],
    "Paint line": [(2, 89), (5, 84), (1, 70)],
}
print("Group             before  phase 1  phase 2   (Lex,8, dBA)")
for g in before:
    print(f"{g:<16} {lex8(before[g]):7.1f} {lex8(phase1[g]):8.1f} {lex8(phase2[g]):8.1f}")

Group             before  phase 1  phase 2   (Lex,8, dBA)
Press operators     96.9     91.0     84.6
Fabricators         95.8     95.8     90.6
Paint line          93.3     85.5     85.5

The paint line group drops close to the limit with the air nozzles alone. Press operators improve by several decibels in phase 1 and are brought to around the limit by the enclosures in phase 2. Fabricators improve less, because welding and shearing remain, so they will need hearing protection for the foreseeable future. Hearing protectors therefore remain part of the program, but the exposures they must control are much lower.

Step 3: administrative controls

The coordinator adds a few administrative measures: grinding is concentrated at two booths rather than done anywhere in the bay; the break room is relocated away from the stamping wall and soundproofed; maintenance work on presses is scheduled when neighboring presses are stopped where possible; and walkways are rerouted so that assembly workers no longer pass between the presses. Job rotation is considered for press operators but rejected, because it would bring more workers into high exposure without reducing the total.

Step 4: hearing protection

Protector selection is based on each group's exposure after phase 1 controls, derated attenuation, the noise spectrum and the needs of the work. The coordinator buys a fit testing system and trains two staff to use it.

Step 5: training, zones and supervision

Every worker in the program receives a 45-minute session with hands-on fitting and a fit test, followed by short toolbox talks every quarter. Supervisors receive an extra session on enforcing zones, checking fit visually and handling complaints. The noise map is used to mark zone boundaries with floor tape and signs, and the rule is simple: everyone entering a marked zone wears hearing protection, including managers and visitors. Dispensers and a selection of protectors are placed at every zone entrance.

Step 6: audiometric testing

Audiometric testing is required under 1910.95(g) for all employees at or above 85 dBA. A provider is contracted to conduct baseline tests for all workers in the program within the first six months, after at least 14 hours without workplace noise, and annual tests thereafter, with review by an audiologist. New hires receive a baseline before their first noisy shift where possible. Standard threshold shifts trigger the follow-up in 1910.95(g) and recordkeeping review under 1904.10.

Step 7: evaluation and budget

The program sets measurable indicators and a budget, which the coordinator presents to senior management with the hearing loss claims as context.

costs = {  # first-year costs, illustrative
    "Noise survey by hygienist": 9000,
    "Phase 1 engineering controls": 1500 + 6000 + 2400,
    "Grinding improvements and ceiling baffles": 22000 + 40000,
    "Fit testing system and training": 7500,
    "Protectors (75 workers)": 75 * 120,
    "Audiometric testing (75 workers)": 75 * 45,
    "Training time (75 workers, 1.5 h at $40)": 75 * 1.5 * 40,
}
for item, c in costs.items():
    print(f"{item:<44} ${c:>9,.0f}")
total = sum(costs.values())
print(f"{'Total first-year cost':<44} ${total:>9,.0f}")
print(f"Cost per worker in program: ${total / 75:,.0f}")

Noise survey by hygienist                    $    9,000
Phase 1 engineering controls                 $    9,900
Grinding improvements and ceiling baffles    $   62,000
Fit testing system and training              $    7,500
Protectors (75 workers)                      $    9,000
Audiometric testing (75 workers)             $    3,375
Training time (75 workers, 1.5 h at $40)     $    4,500
Total first-year cost                        $  105,275
Cost per worker in program: $1,404

The first-year cost is substantial but modest compared with the cost of hearing loss claims, lost productivity from communication problems and the human cost of permanent hearing loss and tinnitus. The press enclosures are budgeted separately for year two.

Reviewing a weak draft

Before the coordinator arrived, a consultant had drafted a short program for Larkspur. Reviewing it is a useful test of everything in this course.

Bringing it together

The Larkspur program illustrates the main lessons of this course. Assess before acting, and assess people, not just places. Rank sources and attack the dominant ones first. Treat hearing protectors as a necessary but fragile last line of defense, chosen with derating and fit testing, and worn all the time in zones. Use audiometric testing as the program's report card, with follow-up for every significant shift. Give the program an owner, resources and measurable targets. And remember that the goal is not compliance on paper but workers who retire with the hearing they started with.