As acoustical and vibration consultants, we are occasion- ally called upon to make measurements inside animal facilities. In some cases, the institution's interest is in
protecting their animals from additional noise and vibration
due to construction in, or adjacent to, the facility. In other
cases, the institutions are interested in evaluating a new or
renovated space that may hold animals. A typical measurement involves a monitoring system capable of measuring floor
vibration and sound, both audible and ultrasonic.1 Operating 24 hours a day, these systems are used to archive data,
send alarms at pre-set levels (e-mail and text), and provide
real time viewing on the internet. During off hours and on
weekends the data provides an excellent look at the levels the
animal population experiences, in the absence of construction.
In addition to long term monitoring, we also receive requests
to specifically measure for ultrasonic noise and, if high levels are present, to locate the source. In some cases we have
identified ultrasonic noise levels that are dangerous to animals,
in particular, to rodents. In these instances we use portable
systems to identify the offending sound source.
WHY IS ULTRASOUND IMPORTANT?
It is important to clarify what is meant when discussing “
ultrasound” as the term applies to animal facilities. Ultrasound, or
ultrasonic sound, is defined as sound with frequencies above
the range of human hearing. Human hearing is generally considered to be within the range of 20 Hz to 20 kHz. 2 The hearing
range of laboratory animals can range from 500 Hz to 100 kHz,
depending on the species. Rats and mice are particularly sensitive to the higher frequencies in this range.
Note that the ultrasonic spectrum does not end at 100 kHz. The
sound generated during ultrasonic imaging can reach 2 MHz or higher.
This is still considered ultrasound. These frequencies are at least 20
times higher than those in the range of animal hearing. Thus, care
must be taken when referring to the “ultrasonic range.”
Behavioral studies have shown that the hearing threshold
for rats is 10 dB SPL3 at 38 kHz4 and for mice the threshold
level is about 20 dB at 50 kHz. 5 At very high exposure levels,
ultrasound has been shown to cause seizures and even death
in small laboratory animals. It can also confound research by
adversely affecting normal behavior. Faith and Miller6 cite an
extensive list of publications documenting the negative effects
of ultrasonic noise exposure, including the induction of sei-
zures in susceptible strains. Castelhano-Carlos and Baumans
write “Strikingly, exposing rats to ultrasounds of 50–80 kHz at
80–90 dB in the four days during the mating period reduced
fertility by 73.2% and productivity by 84%.” 7
CASE STUDY: SOLVING AN EXISTING PROBLEM
A subpopulation of mice was experiencing seizures while being
transported out of their holding rooms. We visited the facility
and measured ultrasound (up to 80 kHz) throughout the facility; in the holding and procedure rooms, as well as the hallways
connecting the rooms.
This facility was equipped with motion detectors that turned on
the lights when people were present. We found that the motion
detectors in the corridors were emitting extremely high levels of
ultrasound. From the outward appearance of these detectors it was
obvious that two different types of detectors had been installed.
Not surprisingly, the ultrasonic tone emitted by each type of detector was different. Figures 1 and 2 show the results of our measurements. The units most commonly in use, labeled Detector Type 1
on the graph, emitted ultrasound at 33,700 Hz. The less common
units, labeled Detector Type 2, emitted ultrasound at 40,000 Hz. In
both cases we measured levels as high as 100 dB at a distance of
about one foot below the devices and about 85 dB at a distance of
20 feet. Animals transported across the hallway inevitably passed
within 20 feet of the detectors.
We presented our results and presume that the motion detectors
have been replaced with detectors that do not emit ultrasound.
CASE STUDY: TESTING BEFORE OCCUPANCY
An existing non-animal facility was undergoing a fit-out to
house small animals. We were asked to measure the baseline
vibration and noise prior to occupancy. We observed very high
levels of ultrasound; 31,500 Hz at a level of approximately 97
dB. Again the source was traced to a motion detector. We informed our client of the potential issue and remedial action was
taken to replace the detectors.
CASE STUDY: THINKING PROACTIVELY
An existing animal facility was being renovated. As part of
the renovation, the florescent lights were being upgraded to
LED bulbs. The project owners were aware of the potential of
electrical equipment to produce ultrasonic sound and wanted
to proactively determine the suitability of the new lighting in
Ultrasound in the animal laboratory
Concerns, measurement, mitigation, and planning