Sulfur hexafluoride (SF6) is a colourless, odourless gas which is produced from the reaction of sulfur with fluorine gas. It is a very unreactive gas which has a density about five times greater than that of air.
Sulfur hexafluoride has a very low toxicity but, as with other gases, it poses an asphyxiation hazard as it can displace air. Its high density means that it will accumulate in low-lying areas and therefore, good ventilation must be ensured in an area where the gas has been released.
When inhaled, sulfur hexafluoride has the effect of lowering the timbre of the voice, the opposite effect of a gas of low density, such as helium. Inhaling sulfur hexafluoride is very dangerous as the high density of the gas makes it difficult to expel from the lungs. Therefore, there is a significant risk of death by asphyxiation in carrying out this activity. Inhaling any inert gas can have serious health consequences and can potentially lead to asphyxiation; please see the references below for more information about the dangers of inhaling industrial gases.
Sulfur hexafluoride is a potent greenhouse gas, which does not break down in the atmosphere, and has a very high global warming potential 23,900 times that of carbon dioxide. Due to its low reactivity, the only way to dispose of sulfur hexafluoride is to release it to the atmosphere. As it is a greenhouse gas, the importation of sulfur hexafluoride is subject to licensing and handling requirements and its cost is quite high—probably prohibitive for most schools.
|Taking into consideration the asphyxiation hazard of using sulfur hexafluoride, as well as the environmental concerns, Science ASSIST does not endorse the use of sulfur hexafluoride in schools and recommends that schools do not carry out any activities, experiments or demonstrations using sulfur hexafluoride.|
Substitution of a safer alternative
To demonstrate a gas with a greater density than air, the less hazardous and cheaper alternative to sulfur hexafluoride is carbon dioxide, which has a density 1.6 times that of air. This property of carbon dioxide can be demonstrated by floating bubbles on a bed of the gas or by ‘pouring’ the gas from a jug or bucket into a vessel which contains lighted candles of different heights.
Dry ice also has associated cryogenic and asphyxiation hazards; please see the Science ASSIST Standard Operating Procedure 'SOP: Handling dry ice' for more information.
Another alternative is to show a YouTube video that demonstrates the properties of sulfur hexafluoride. For example, https://youtu.be/DzLX96VWTkc demonstrates the buoyancy of the gas. (Note: We advise against promoting videos that encourage the extremely hazardous practice of inhaling this gas.)
Australian Government Department of Sustainability, Environment, Water, Population and Communities, 2012, Sulfur hexafluoride (SF6) and the equivalent carbon price, https://web.archive.org/web/20130509133305/http://environment.gov.au/atmosphere/ozone/sgg/equivalentcarbonprice/publications/pubs/fs11-ecp-sf.pdf (Link updated to Internet Archive copy, July 2019)
Bennett H., 2019. Magnificent molecules: Sulfur hexafluoride. Royal Society of Chemistry website. https://edu.rsc.org/magnificent-molecules/sulfur-hexafluoride/4010538.ar... [Reference added February 2020]
Scottish Environment Protection Agency, Scottish Pollutant Release Inventory, Sulfur hexafluoride, http://apps.sepa.org.uk/spripa/Pages/SubstanceInformation.aspx?pid=10 Accessed February, 2015.
Wilkinson, Steven. Science Business Manager, Investigative Chemistry Division, ChemCentre, Curtin University, Bentley W.A. (Personal communication, February, 2015)
Further information on the dangers of inhaling helium, sulfur hexafluoride and other industrial gases
Australia New Zealand Industrial Gas Association, Safety Advice No. 22, The Dangers of Industrial Gas Abuse, October 2012, http://www.anziga.org/public/editor_images/Publication/142_-022_Safety_A...
ELGAS LPG, Be Gas Wise - Community Service Announcement, November 16 2014, https://youtu.be/0In9O0CXAFs
Hahn, Eric, ELGAS LPG Gas Blog, Helium Balloon Gas Safety, http://www.elgas.com.au/blog/1030-helium-balloon-gas-safety-don-t-be-a-d... Accessed February 2015
News Limited, Inhaling gas from helium balloons no laughing matter, it can kill, November 15, 2014, http://www.news.com.au/lifestyle/health/inhaling-gas-from-helium-balloon...