Almost everyone has inhaled the helium from a balloon at some point or another, and then roared with laughter as we all sound like Alvin from the Chipmunks cartoon program. So imagine the fun deep sea divers must have as they breathe a mixture which contains helium for diving to unusually deep depths for relatively long periods of time. But why is it that the gas can change our voices in this way?
How our voices work
We all know that we have a so called voice box, more scientifically called the larynx. What this consists of, in effect, is a triangular shaped opening in our trachea, the tube through which oxygen passes into our lungs, and across the sides of this triangular opening are two horizontal folds of mucous membrane, known as the vocal folds or vocal cords.
When we exhale, the air leaving our lungs causes the underside of these vocal chords to vibrate, which causes the movement of the air molecules. By manipulating these molecules by moving our tongue in various ways and incorporating this with the movement of our lips, we are able to produce the wide range of different sounds which we use to speak. As we all have lungs and necks suited to each of our individual bodies, we all produce a different sounding voice unique to us as individuals, as although we all have the same voice making mechanisms, the size of these mechanisms is unique to all of us.
Why helium creates a different sound
The driving force behind speech is the air which vibrates our vocal chords when we exhale. As the air that we breathe is composed mostly of nitrogen (78%), and oxygen (20%), with smaller percentages of other gases like argon and carbon dioxide (both less than 1%), the molecular weight of the air which vibrates our vocal cords is the molecular weight of these elements present in air. This is further enhanced by the fact that the speed of sound through air is set at around 331 m/s when the air is composed of these elements. We are used to hearing noise, in this cases people’s voices at this speed of sound.
When helium is inhaled however, the situation in the voice box is changed dramatically. Helium isn’t a regular constituent of Earth’s air, and will quickly dissipate through our atmosphere into space when released into the atmosphere. This is because the molecular weight of helium is much lower than that of our planet’s air, and therefore much lighter. What this means for our voice boxes is that the molecules in helium are manipulated much faster than those in the gases we normally breath. This in turns means that the path of resistance for sound is far less in helium, so that the speed of sound through helium is greatly increased.
Therefore, the strange effect helium has upon our voices is due to the increased speed of sound at which helium allows our voice to travel through the air, which is now composed of helium due to having inhaled helium. The vocal cords are manipulated in exactly the same way, but have a greater effect upon the helium molecules. Expressed another way, sound travels in wavelengths. Due to helium being lighter than regular air, the wavelength through helium is much shorter than through regular air, which leads to a faster, more high pitched sound. As your voice moves into the resistance of the heavier air however, this wavelength will again be slowed down, so that the noise which reaches other people’s ears is still your usual voice, but at a higher pitch.
Dangers of inhaling helium
As helium isn’t a usual constituent of the air which we breathe, breathing helium isn’t at all conducive to our health. This is because inhaling helium places a strain upon our lungs, as our bodies can’t respire helium. This basically means that whilst we are breathing helium, no oxygen is reaching the cells of our body, so that inhaling helium is the equivalent of holding our breath. As holding our breath can obviously lead to unconsciousness if held for too long, the same can happen if we don’t breathe after having inhaled helium.
This isn’t too much of a problem as to speak we naturally have to exhale, which will lead to an instinctive inhalation, purging the helium from our lungs. Also, the helium used to fill up balloons also has some oxygen content.
Helium which is kept in canisters should never be inhaled however, as in a canister the helium is under high pressure. This means that when this helium enters your lungs, which are at a much lower atmospheric pressure to the inside of the canister, the lungs will expand rapidly and very likely burst, which of course results in death.
The only time that helium should be and is regularly inhaled from a tank is in the example of deep sea diving when trimix solutions are used. This means that the air in the diving tanks is composed of oxygen, nitrogen and helium, with helium forming the main component. This is to prevent oxygen or nitrogen narcosis, a kind of gas induced drunken stupor, which occurs when nitrogen and oxygen are breathed under the increased pressures found in deep water which increases lung pressure. As the pressure of the oxygen and nitrogen matches the increased pressure found at depth when entering the lungs, helium has to be added to reduce the percentage of oxygen and nitrogen breathed, as less oxygen and nitrogen breathed at increasing depths is equivalent to the normal levels of oxygen and nitrogen breathe on the surface due to the increased pressures.