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”
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
Sound level distribution is consistent with an acoustic mode:
Droom =N(wavelength of sound/2); N an integer 1,2,3,…
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.