How to Measure Noise on Your Own Jobs
Why this matters
Published tool levels give you a range ten decibels wide, and ten decibels is a factor of ten in sound energy. Whether your crew is over the line depends on your blades, your materials, your enclosures and how many minutes each tool actually runs, none of which a table knows. A shop that has measured its own five loudest tasks can make every later hearing decision from its own numbers: which jobs need muffs over plugs, who goes into an audiometric program, and whether a quieter tool earns its price. A shop that has not is guessing, usually low.
This card is the method. Which limit applies, and how a day's dose is read against it, is owned elsewhere: see related: Noise: The 85 Decibel Line and Hearing Conservation.
The instrument decides what the number can be used for
Three tools, three jobs:
- A phone app. NIOSH publishes a free sound level meter app for iOS devices, and in NIOSH's own laboratory testing the better apps read within a couple of decibels of a reference meter under those test conditions. With the phone's own microphone it is a screening tool: good for "is this task anywhere near 85 dBA," not for a compliance record. An external calibrated microphone that plugs into the phone narrows the error.
- A sound level meter. A Type 2 (or Class 2) meter, built to ANSI S1.4 or IEC 61672, is the accepted field instrument for spot readings of a task. It reads what is happening at one place and one moment, or averages over the minutes you hold it there.
- A noise dosimeter. A small meter, built to ANSI S1.25, clipped to the worker's shoulder with the microphone near the ear, worn for the whole shift, integrating every minute into a dose. For a mobile worker moving between tools, only a dosimeter captures the day as lived. It is what OSHA's monitoring requirement at 29 CFR 1910.95(d) is normally met with, and many models log OSHA and NIOSH settings at the same time.
The phone tells you where to send the dosimeter. It does not replace it, for reasons step 8 lays out.
The steps
Pick the five loudest tasks from your tickets, not from your ears. Pull a month of jobs and list the tools that ran longest at high level: blowers and trimmers for a lawn crew, rotary hammers and grinders for an electrician, cut-off saws for a hardscape crew. Reason: the tasks that set the dose are the ones that combine level and minutes, and the loudest-sounding tool is often not the one that runs longest. Skip it and you measure the dramatic tool and miss the one that runs three hours a day.
Check the instrument against a known level before and after. A sound level meter is checked with an acoustic calibrator, a small device that produces a fixed tone (commonly 94 or 114 dB at 1,000 Hz), before the session and again after. A phone app is checked by reading it side by side with a calibrated meter on a steady source and setting the app's offset to match. Reason: a microphone drifts, and a phone's microphone is tuned for speech. Skip it and every reading inherits an unknown error; if the after-check differs from the before-check by more than about 1 dB, the session's readings are suspect.
Set A-weighting and slow response, and know where peak lives. A-weighting (dBA) approximates how the ear responds and is what both OSHA and NIOSH limits are written in. Slow response averages over about a second and is the setting OSHA's noise standard specifies. For impulse tools such as nail guns and powder-actuated tools, read the peak (dB peak, often C-weighted or unweighted) separately. Reason: a slow-response average turns a 140 dB peak into a modest-looking number. Skip it and the most damaging tool on the truck reads as the safest.
Put the microphone at the ear of the person doing the work. Readings belong in the operator's hearing zone, which the OSHA Technical Manual describes as a sphere about two feet in diameter around the head; in practice, within about six inches of the ear facing the tool. The operator cannot hold a meter while running a grinder, so a second person holds it, or the operator wears it clipped at the collar. Hazard: the person holding the meter is now beside a running tool, so they wear hearing protection, safety glasses and whatever the task requires, stand beside the operator rather than in the tool's discharge path (the blower's air stream, the trimmer's throw, the grinder's spark line), and never reach toward a moving blade or a mower deck. Reason: a reading from across the yard can be 6 dB or more low, which is a quarter of the energy.
Measure a representative stretch, and read the average, not the needle. Record at least two minutes of normal work, the way the task is actually done, including the pauses. Use the meter or app's equivalent continuous level, written LAeq, which is the energy average over the time you held it there. Note the maximum too. Reason: the needle swings with every pass; the LAeq is the number that goes into a dose. Skip it and you write down the loudest moment you happened to see.
Keep wind and handling off the microphone. Outdoors, fit the foam windscreen, and keep the microphone out of any air stream, including the one a blower makes. Do not let the phone rub on a jacket. Reason: wind across a microphone reads as low-frequency noise that is not reaching the ear in that form. Skip it and a blower measurement is inflated by the blower's own wind.
Log the task, the tool, the material and the minutes. Every reading gets a line: the task, the tool and blade, the material, indoors or out, the distance, the LAeq and max, and how many minutes per day that task typically runs from the tickets. Reason: a level without minutes cannot become a dose, and a dose is what the limits are written in. Skip it and the readings cannot be reused next year when a new hire asks.
Escalate by result, and know what the phone cannot do. Below 80 dBA LAeq, the task contributes little under either yardstick. From 80 to 85, it depends on minutes, so work out the day. Above 85, protect the crew now, and put a dosimeter on the worker for a full shift before deciding who enters an audiometric program. The phone cannot integrate a whole shift unattended in a pocket (a covered microphone reads low), cannot follow a worker between tools reliably, carries no type rating, and its result is not a monitoring record. Skip the dosimeter and a program decision rests on two minutes of a phone held by someone else.
A worked measurement: one lawn crew, one day
A three-person lawn crew; the shop wants to know whether the crew lead needs more than plugs. A coworker holds a phone with the NIOSH app, offset checked against the shop's Type 2 meter at the start and end of the day (both checks within 0.5 dB of each other), at the lead's ear.
NOISE LOG crew lead route day (screening, phone)
Task Tool LAeq Max Min/day
Blowing gas backpack 99 104 120
Trimming gas trimmer 96 101 90
Mowing stand-on mower 88 93 180
Driving truck cab 72 78 90
Total minutes 480
Notes: windscreen on; held clear of blower air
The ticket review set the minutes, and they total 480, an 8-hour day. Under the NIOSH yardstick (85 dBA criterion, 3 dB exchange), the allowed times are about 0.32 hours at 99, 0.63 hours at 96, 4 hours at 88 and 161 hours at 72, so the doses are 2.0 divided by 0.32, about 6.35, plus 1.5 divided by 0.63, about 2.38, plus 3.0 divided by 4, 0.75, plus a negligible 0.01: a total of 9.49, a TWA of about 94.8 dBA. Under OSHA's 5 dB method the allowed times are about 2.30, 3.48 and 10.56 hours, the 72 dBA drive is below the 80 dBA threshold and does not count, and the dose is 0.87 plus 0.43 plus 0.28, or 1.59, a TWA of about 93.3 dBA. Lawn maintenance is general industry, so 29 CFR 1910.95 is the standard, and 93.3 is over its 90 dBA PEL.
The shop's calls, and why. Blowing is the target: it is about two-thirds of the NIOSH dose (6.35 of 9.49) from a quarter of the day (120 of 480 minutes), so a quieter blower or a shorter blowing route moves the total more than anything done to mowing. Plugs alone are marginal for blowing: at 99 dBA, a foam plug labeled NRR 32 and derated the way OSHA's technical manual does it leaves roughly 86 or 87 dBA at the ear even when fitted well, and a poorly fitted one far more, so the lead gets muffs over plugs for that task (see related: How to Fit Earplugs So They Actually Work). A dosimeter goes on the lead next week, because a screening reading over the PEL starts the monitoring and program duties under 1910.95, and those rest on a proper measurement.
What changes the answer. If the crew switched to battery blowers that read, say, 90 dBA at the ear, the NIOSH blowing dose falls from 6.35 to 2.0 divided by 2.52, about 0.79, and the day's total drops from 9.49 to about 3.9. Still over the recommendation, now dominated by trimming, and a different conversation about the next tool to replace.
The failure mode. The first attempt at this survey had the lead hold the phone himself at arm's length while blowing, pointed toward the air stream. The blower read 106 with wind roar and the trimmer read 89 from an arm's length away; one task was overstated and the other understated, and the shop nearly spent its money on the wrong tool.
How to verify you got this right
- The before and after calibration checks agree within about 1 dB, and the log says so.
- Every task line carries minutes, and the minutes add to a real day (here, 480).
- The dosimeter result, when it comes back, lands within about 3 dB of the screening TWA. If it does not, trust the dosimeter and find out why the phone disagreed, usually microphone placement or wind.
- Re-measure when a tool, blade or route changes, not on a calendar.
References
- 29 CFR 1910.95, Occupational Noise Exposure, including the monitoring requirement at (d)
- OSHA Technical Manual, Section III, Chapter 5, Noise, for instrument settings and the hearing zone
- NIOSH Sound Level Meter app and NIOSH's published evaluation of smartphone sound measurement apps
- ANSI S1.4 and IEC 61672 (sound level meters), ANSI S1.25 (personal noise dosimeters), the instrument standards a purchased meter states compliance with
- See related: Noise: The 85 Decibel Line and Hearing Conservation; How to Fit Earplugs So They Actually Work