Event planners should take health & safety aspects at their events very serious. Most of them do this already. As part of the licensing requirements event planners need to create (and implement) a risk assessment. Accidents still happen though.
The following article discusses the risks of amusement rides at events. The article starts out with some gruesome examples but I guess that brings home the message.
Kevin Moore works in risk management services in America and has written this article about event safety issues for the Kentucky Forward.