Health concerns arising from low frequency sound in a chemistry lab.

Bill Gibson, Environmental Health and Safety Officer, Risk Management Office, Trent University

Initial Report of Illness

September, 2006, Voice mail:

Staff member working at a computer in a research lab had “passed out”.

Investigation

Several staff (not all) experiencing periodic bouts of illness;

Illness appeared to be limited to a single research lab;

Rapid recovery on leaving the lab (less than one hour);

Symptoms had been experienced for about one week.

Investigation

Reported symptoms include:– Nausea– Dizziness– Inability to focus– ‘Faint’ feeling (no actually loss of consciousness)– Some reported feeling a ‘pressure change’ in the

lab

Investigation

Lab work temporarily halted Consultations included

– Lab staff including Principal Investigator (review of lab operations)

– Science Facilities Manager– Physical Resources (Mechanical/Electrical) staff and a

review of air supply/exhaust systems (physical and reports)– Third party Environmental Consultants, colleagues

Investigation

Lab involved with studies of biogeochemistry of freshwater

Carbon dioxide <<1000 ppm

No evidence of combustion gases

No evident source of contamination

Investigation

Lab staff agreed to resume work and keep diary of symptoms, but symptoms return by mid-morning;

PI researched symptoms of exposure to sound <20 Hz and found a good match with symptoms;

Pinchin Environmental retained to conduct a sound survey

Chemical Sciences Building

Opened September, 2004;

35,532 sq. ft. Houses

– Chemistry Department– Teaching labs– Research labs

(Chemistry, Environmental Science)

“State-of-the-Art”

Chemical Sciences Building

The Survey

Acoustic data measured with a Bruel & Kjaer (B&K) Model 2260 Precision Integrating Sound Level Meter configured in 1/3 octave mode.

The Survey

The Survey

The Survey

Sound level distribution is consistent with an acoustic mode:

Droom =N(wavelength of sound/2); N an integer 1,2,3,…

The Survey

Conclusions

Sound peaks occur in this lab, where room dimensions ‘match’ the wavelength of the sound

Low frequency sound explains the illness experienced when working at the fume hoods at either end of the lab.

Conclusions

The main fumehood duct appears to be generating the low frequency sound;

Attempts to confirm these findings by changing the exhaust fan RPM failed then the entire system shut down (believed due to control system issues)

The Solution

Inhibit motion of the duct walls by installing neoprene-lined ‘hoops’ at several locations on the duct.

Follow up

Separate maintenance concerns led to the discovery that one of the fume hood dampers had worked itself closed;

Re-opening the damper reduced static pressure, duct vibration and fan RPM;

There have been no further reports of health concerns;

Hoops have not been installed.