As anyone with access to news, social media, or other people will know, protests are currently happening worldwide. Sparked by the unjust death of George Floyd, the US has seen protests representing the Black Lives Matter movement in every state, with the national guard being deployed in at least 23 of these (Haddad, 2020).
Predominantly used by the military, there have been reports of a number of police departments using LRAD in response to the protests. While many claim this to be for communication, sources show that at least Portland PD have used these as a sonic weapon for crowd dispersal by “[emitting] a tone that is very hard to be around” (Jaquiss, 2020).
LRAD are Long Range Acoustic Devices, systems designed to carry messages at high loud levels over long distances. These systems are primarily developed by Genasys, a company who claim on their website that they create “solutions to help keep people safe” (Genasys Inc., 2020). Genasys state their products are able to communicate messages up to 5,500 metres, which begs the question – how loud does that make it at short range?
There are a lot of figures floating around regarding this level, with some claiming a level of over 150dB, but the most common figure that comes up appears to be 137dB at 1m. If you have no experience with sound or noise control related fields, this figure may not hold any significant meaning, so I will try break it down briefly.
The decibel is a logarithmic unit, used in this case as a measurement of sound level. The measurement of sound is not a linear scale for example an increase of 10dB is ten times louder. Due to this we have to use logarithmic equations to calculate different sound levels.
If we take the sound level at 1m to be the sound power level, we can calculate how loud it will be at certain distances with this equation:
For this LP represents the sound pressure level (SPL) at a given distance, LW the sound power level (taken as 137dB), and S the distance.
Using this equation, the SPL at 100m would be 117dB and at 10m it would be 127dB. For reference, a jet engine produces around 120dB at close range (Pulsar PLC, 2019). Granted, this will vary with outdoor conditions, but for these purposes, this is accurate enough.
There are laws in place stating the safe exposure levels of noise in the workplace, after a certain level, employers are obliged to take action and provide protection. In the UK, the regulations are as follows:
|80dB||“Employers must assess the risk to workers’ health and provide them with information and training”|
|85dB||“Employers must provide hearing protection and hearing protection zones”|
|87dB||“Above which workers must not be exposed”|
These regulations are in place to protect workers from noise exposure related hearing loss and are fully detailed in the Control of Noise at Work Regulations 2005. Exposure to 85dB requires hearing protection as exposure to these levels can cause permanent hearing damage. Over 100dB, very little exposure is needed to cause loss of hearing.
Safe noise exposure is calculated as an acceptable amount over a working day – based on 8 hours – comparable to a maximum daily dose. As noise is increased, the acceptable amount of exposure is reduced. In the UK, this is calculated using ISO 9612:2009 as a standard method. Following this standard, an increase of 3dB halves the time before reaching this maximum dose.
Following this, the maximum exposure for 88dB is four hours, 91dB is two hours, etcetera. By 120dB, this time is reduced to a matter of seconds. Using this pattern, at 100m the maximum exposure in a day to LRAD is only fourteen seconds. If you are 10m away from the system, the maximum exposure is less than two seconds. If these levels are imposed by law for all workplaces, protective measures should be in place for protesters and the general public.
In the case of extremely loud sounds, the ear has somewhat of a defence mechanism, this is called the acoustic of tympanic reflex. This reflex causes muscles – stapedius and tensor tympani – in the ear to contract when exposed to sounds over 75dB. The stiffening reduces the transmission of sound through the ossicles, protecting the inner ear from damage (Howard and Angus, 2006). It takes up to 120ms for the muscles to contract in this way, so it is not an instantaneous reaction to sounds of this level. Being exposed to noise as loud as LRAD can still cause hearing damage before the tympanic reflex has enough time to react to it.
One of the most commonly known forms of hearing damage is tinnitus. If you have ever been to a loud concert and have come out with a ringing in your ears, you have experienced a level of what this condition is like. In some cases, that ringing will go away within a day or two, but the effects can be permanent. While this condition can be caused by a number of things, one of the most common causes is high levels of noise exposure. High levels of exposure can cause damage to the small hairs in the inner ear, which causes conditions such as tinnitus (Davis, 2017).
As well as tinnitus, the flattening and tearing of these hairs – cilia – can lead to a loss of hearing sensitivity. Permanent hearing reduction comes when these hairs are damaged to an extent that overwhelms the healing.
The hairs that pick up higher frequencies are the first which sound reaches in the inner ear. Due to this, hearing loss often occurs first at higher frequencies. A degree of this happens through presbycusis with age, but this can be accelerated by dangerous levels of sound exposure.
Another form of hearing damage is hyperacusis, a decreased threshold of discomfort from sounds. Essentially, this reduces the threshold of pain for hearing. This can range from mild discomfort from louder sounds to discomfort caused by everyday sounds.
Fears of hearing damage such as this, caused by the excessive noise levels of LRAD have in the past left some warning friends “if you hear this, plug your ears and run” (Kesslen, 2015). Without any hearing protection, there is little else that can be done when faced with such high sound levels. In cities where police are known to use such measures against protestors, some form of hearing protection should be carried.
The Canadian Centre for Occupational Health and Safety gives suggestions of three types of hearing protection to reduce the risks of hearing damage from noise exposure:
“Ear plugs are inserted in the ear canal. They may be remoulded (preformed) or mouldable (foam ear plugs). Disposable, reusable or custom moulded ear plugs are available.
Semi-insert ear plugs which consist of two ear plugs held over the ends of the ear canal by a rigid headband.
Ear muffs consist of sound-attenuating material and soft ear cushions that fit around the ear and hard outer cups. They are held together by a head band”
Most ear muffs are reasonably priced, though may not be practical in the setting on a protest for everyone, they are quite bulky to carry around, and could fall off. While custom moulded earplugs are a very effective form of noise protection, if you are not using them for other purposes they are quite expensive. Foam ear plugs can be bought in bulk for very cheap; these are frequently single use so no harm is done if they are lost, and carrying several pairs allows for helping fellow protesters. If you prefer reusable ones, perhaps to reduce waste, there are a number of options available. Several brands make ear plugs that come in a case which is designed as a keyring – you will be less likely to forget or lose these.
Different types of hearing protection will work for different people, but it is becoming increasingly important to have some form of this when at a protest. Of course, this is primarily crucial in cities where LRAD is known to be used, but there are also high levels of noise from other sources at these events, so having hearing protection regardless would not be unwise.
CCOHS. 2017. Hearing Protectors : OSH Answers. [online] Available at: <https://www.ccohs.ca/oshanswers/prevention/ppe/ear_prot.html> [Accessed 11 June 2020].
Davis, K., 2017. Tinnitus: Symptoms, Treatment, Home Remedies, And Causes. [online] Medicalnewstoday.com. Available at: <https://www.medicalnewstoday.com/articles/156286> [Accessed 10 June 2020].
Genasys Inc. 2020. Communication. Critical To Saving Lives. | Genasys, Inc.. [online] Available at: <https://genasys.com/> [Accessed 9 June 2020].
Haddad, M., 2020. Mapping US Cities Where George Floyd Protests Have Erupted. [online] Aljazeera.com. Available at: <https://www.aljazeera.com/indepth/interactive/2020/06/mapping-cities-george-floyd-protests-erupted-200601081654119.html> [Accessed 9 June 2020].
Health and Safety Executive, 2005. The Control Of Noise At Work Regulations. London.
Howard, D. and Angus, J., 2006. Acoustics And Psychoacoustics. 3rd ed. Oxford: Focal, pp.70-71.
Hse.gov.uk. n.d. HSE – Noise: Regulations. [online] Available at: <https://www.hse.gov.uk/noise/regulations.htm#:~:text=The%20level%20at%20which%20employers,training%20is%20now%2080%20decibels.> [Accessed 10 June 2020].
International Standards, 2009. ISO 9612:2009 Acoustics — Determination Of Occupational Noise Exposure — Engineering Method.
Jaquiss, N., 2020. Portland Police Deployed A “Long Range Acoustic Device” Friday Morning For Crowd Control. [online] Willamette Week. Available at: <https://www.wweek.com/news/2020/06/05/portland-police-deployed-a-long-range-acoustic-device-thursday-night-as-crowd-control-device/> [Accessed 9 June 2020].
Kesslen, B., 2015. ‘Plug your ears and run’: NYPD’s use of sound cannons is challenged in federal court. NBC News, [online] Available at: <https://www.nbcnews.com/news/us-news/plug-your-ears-run-nypd-s-use-sound-cannons-challenged-n1008916> [Accessed 11 June 2020].
MED-EL, 2014. How The Ear Hears Sound | The MED-EL Blog. [online] The MED-EL Blog. Available at: <https://blog.medel.com/how-the-cochlear-understands-so-many-different-sounds/> [Accessed 10 June 2020].
Plc, P., 2019. What Are Decibels, The Decibel Scale &Amp; Noise Measurement Units?. [online] Pulsar Instruments Plc. Available at: <https://pulsarinstruments.com/en/post/understanding-decibels-decibel-scale-and-noise-measurement-units> [Accessed 10 June 2020].