Sound experts spar over appropriate wind turbine noise standards 

MONTPELIER – Acoustic experts representing proponents and critics of industrial wind power squared off for the first round of public hearings on sound decibel standards.

At a meeting Friday in the Capitol Plaza Hotel, Stephen Ambrose, a sound consultant and member of the Institute of Noise Control Engineering, argued that sound levels permitted in Vermont are too high and are causing sleeplessness, distress and other health-related symptoms. [See video, below.]

Presenting the opposite view were Payam Ashtiani, principal for Aercoustics Engineering Limited, and Dr. Chris Ollson, senior environmental health scientist for Ollson Environmental Health. The two experts represented the Department of Public Service and testified that current standards are adequate for protecting public health.

The experts spent a lot of time talking about a Health Canada study from 2012 to 2014 that led to at least eight peer-reviewed publications on wind turbine noise.

“At the end of the day they found that at 46 dBA [decibels adjusted] or less – and 820 feet was the closest home to a project – there was not an association between self-reported or measured determinants of health,” said Ollson.

Based on that research, Ollson concludes that noise levels emitted from industrial turbines at 46 dBA or less – as measured from outside a home – should be an acceptable standard for current and future turbine projects.

Ambrose argued that the dBA limit should be set in the low-30s, and added that a 45 dBA limit is only acceptable for urban environments with other sources of background noise.

In a rural setting, where ambient noise levels are lower, Ambrose said complaints typically start at 30 dBA. If levels hit 40 dBA, local residents start opposing projects. At 45 dBA, residents begin abandoning their homes.

The discussion shifted to how decibel counts should be measured – by averages or by peaks, and for how long a duration. Ashtiani recommended measuring decibel averages over one-minute intervals to help eliminate random noise spikes that contaminate test data. Ambrose countered that spikes come from the turbines and should be part of the measurement.

The experts also discussed appropriate distance limits between homes and turbines. Ambrose said the commonly accepted distance of 10 times the height of turbines is often not far enough, and he cited cases in Australia and New Zealand where people set back 15 to 20 times the height of turbines still reported adverse effects. Ashtiani and Ollson argued against setting distance limits.

Ollson argued that most sound complaints from turbines can be attributed to “annoyance.”

“We’ve known out of the early research out of Europe in the last decade, that what is the larger source of annoyance is visual cue and community attitude towards the projects,” he said.

At the end of the hearing, those who favor stricter sound standards said they were frustrated that they didn’t get enough time to make their case. Members of the PSB said there would be more opportunities for everyone to be heard.