Thomas E. Gill 1, John A. Knox2, Castle A. Williams2, L.V. Boggs2, E. Schumacher2, K. Arney2, N. Bagley2, I. Boatman2, J. Croft2, J. Printup2, J. Rackley2, C. Scarborough2, J. White2, David J. Novlan3
1University of Texas, Geological Sciences/ Environmental Science and Engineering, El Paso, TX, USA, 2University of Georgia, Geography Dept., Athens, GA, USA, 3National Weather Service, Santa Teresa, NM, USA
Portable inflatable amusement devices (PIADs), variously known under many names including “bounce house,” “jumping castle,” “moon walk,” “brinca-brinca,” etc., are popular play structures for children, widely used at both public events and on private property. Since they are air-inflated, comprised of PVC or polyester, generally affixed to the ground only at corners but not always securely, and deployed in flat, open areas, they can be effectively visualized as large, loose, ultra-low-density boulders exposed to wind. It is no surprise that they are vulnerable to aeolian transport.
We have documented and cataloged more than 60 events (reported from various news media sources) between 2000 and 2015 wherein human-occupied PIADs were moved by the wind, sometimes when “properly” anchored, causing injury or death. These incidents, creating a hazard not only to those inside the structures but also to bystanders in the path of the moving mass, have taken place in more than a dozen nations on every inhabited continent, causing at least 270 injuries and multiple fatalities.
Meteorological data from the vicinities of these cases, combined with images/video and media interviews related to these events, have allowed us to understand the aeolian forcings and modes of transport of these “castles in the air”: they are effectively the same phenomena involved in wind transport of sediments. Some PIADs were entrained by synoptic-scale winds related to pressure gradients, fronts, etc.: others were moved by mesoscale winds such as gust fronts from thunderstorms. Intense microscale winds (dust devils, tornadoes) can lift and transport bounce houses as well as soil. Synoptic-scale and mesoscale winds tend to move PIADs in creep and/or saltation, much like mineral grains, while intense microscale wind vortices can physically suspend them vertically and make them take flight (with humans inside), in some cases soaring over houses and trees tens of meters downwind. At least in North America, events are concentrated in the regions and seasons also prone to aeolian sediment transport- during the spring and early summer months, in the drylands from interior California and southwestern deserts to the southern Great Plains.
We conclude with some calculations of the winds and forces required to move PIADs and maintain their transport, and a critical review of current regulations and instructions for securing these objects against aeolian detachment and promoting their safe use. We provide recommendations to (literal) stakeholders on PIAD wind safety, so that in the future aeolian transport will be strictly limited to natural materials.