Data-center noise: construction vs operations, workplace vs neighbors

Construction: pile driving, concrete, steel erection, deliveries and haul routes, temporary generators during commissioning. Hours are set locally. FHWA’s Construction Noise Handbook inventories highway-construction equipment categories and example levels at 50 ft (Table 9.1). Those are construction-equipment facts, not operating-campus ratings.

Operations: cooling plant (chillers, dry coolers, cooling towers, rooftop or yard units), transformers, and emergency generator testing. Mostly steady plant sound, plus intermittent tests. Loudoun County’s public page notes HVAC units and backup generators as common sources, and that much of the complaint load is tonal hum rather than a single loud event.

Emergency stationary engines under the RICE NESHAP (40 CFR 63 Subpart ZZZZ) have limits on hours used for maintenance checks and readiness testing. Under 40 CFR § 63.6640(f)(2), that allowance is up to 100 hours per calendar year for the purpose specified there. Related paragraphs also discuss non-emergency operation caps (including a 50-hour path). These are air-toxics operating-hour rules.

What that means for a proposal review: a test schedule is a fair ask. Do not present the hour cap as a property-line noise limit. Loudoun County’s public page separately states that most data centers there run backup diesel generators about one hour, once per week, for mandatory testing.

Mostly local governments. Under the Noise Control Act framework, EPA established the Office of Noise Abatement and Control (ONAC). EPA’s Title IV noise page states that in 1981 the Administration concluded noise issues were best handled at the state and local level, ONAC closed, and primary responsibility moved to state and local governments. EPA’s 1974 Levels Document remains guidance: 70 dB (24-hour) identified to prevent measurable hearing loss; 55 dB outdoors and 45 dB indoors identified for activity interference and annoyance.

• General industry: 29 CFR 1910.95. Table G-16 PEL is 90 dBA for an 8-hour day. Hearing conservation program required at 85 dBA 8-hour TWA.
• Construction: 29 CFR 1926.52 Table D-2 uses the same 90 dBA / 8-hour schedule.
• NIOSH REL: 85 dBA averaged over an eight-hour workday (recommendation, stricter than the OSHA PEL).

These protect electricians, HVAC/R techs, pipefitters and other trades on the job. They are not fence-line standards for neighbors. Related DCST pages: NFPA 70E checklist (electrical safety, not noise), on-site systems.

1. Construction hours and haul routes, named in the proposal (not “per local rules” alone).
2. Operations equipment list (chillers, dry coolers, cooling towers, rooftop/yard units, transformers) and locations relative to nearest property lines and homes.
3. Generator test schedule for emergency stationary engines (hours, days, expected duration). RICE NESHAP hour caps are air rules; still ask for the schedule in plain words.
4. Named AHJ ordinance and the exact limits the proposer relies on (zoning district, day vs night, measurement point, A-weighting vs other methods).
5. Dated acoustic study by a named firm, if one exists (pre-construction and any required post-occupancy study).
6. Whether the study addresses tonal / narrow-band hum and low-frequency content, not only a single A-weighted number. Some counties note dBA alone under-states steady tonal noise.

• Invented “typical data center is X dB” claims with no named facility filing or ordinance.
• Treating OSHA or NIOSH workplace numbers as neighbor/property-line limits.
• Treating RICE NESHAP 100-hour testing allowances as a noise ordinance.
• Pasting FHWA highway-construction equipment levels onto an operating campus.
• “Quiet campus” marketing without a named ordinance citation or dated acoustic study.

Loudoun County, Virginia (home to a large data-center cluster) publishes a noise-and-air page that states:

• Data centers must submit a pre-construction noise study at site-plan review and a post-construction noise study between 1 and 12 months after the first Certificate of Occupancy.
• Maximum sound levels are measured in dBA at the receiving property line; for residential properties the published maximum is 55 dBA.
• Much complaint traffic is about tonal hum; the county notes dBA-only rules can under-capture tonal and low-frequency content, and that plan/zoning amendments on this topic have been in work.
• Most data centers there run backup diesels about one hour, once per week for mandatory testing (county’s published description).

Cite Loudoun as one worked example of the pattern (property-line limits by zoning district, required studies, generator-test practice). Other counties differ. Always open the AHJ text for the site you are reviewing. County hub: loudoun.gov/datacenters.