Noise & Health
Boulder’s noise limits are not taste standards. They are health standards — and the science behind them has only gotten stronger since they were written.
- Where 55/50 come from. The limits trace to the U.S. EPA’s 1974 determination of the outdoor level "requisite to protect the public health and welfare with an adequate margin of safety" (55 dB), and to World Health Organization guidance identifying 55 dB as the threshold of serious annoyance.
- Nights matter most. WHO’s health-based night guideline is 40 dB — ten decibels below Boulder’s night limit. WHO places the thresholds for hypertension and heart-attack risk at 50 dB at night: exactly where Boulder’s limit begins. There is no margin of safety in our night limit.
- What the medicine shows. Chronic noise exposure raises ischemic heart disease risk about 8% per 10 dB (rated high-quality evidence in WHO’s systematic review). Sleep disruption begins at levels as low as 33 dB at the pillow — harm does not require waking. A 5 dB increase in chronic exposure was associated with a two-month reading delay in children.
- The bass problem. Standard meters under-count bass. At equal readings, bass-heavy amplified music is roughly 3–6 dB more intrusive than ordinary noise — a party that "complies" on a meter can still be shaking a neighbor’s windows. Colorado state noise law reflects this.
More than half of University Hill’s noise complaints occur during sleeping hours. The people absorbing that exposure include children, night-shift workers, the ill, and the elderly.
Sources
- U.S. EPA, Levels Document (1974)
- WHO, Guidelines for Community Noise (1999)
- WHO, Night Noise Guidelines for Europe (2009)
- WHO, Environmental Noise Guidelines for the European Region (2018)
- Basner et al., The Lancet 383:1325 (2014)
- van Kempen et al., IJERPH 15:379 (2018) — WHO cardiovascular review
- Leventhall, Noise & Health 6(23):59 (2004) — low-frequency noise