Typically, those releases are enforceable against normal hazards and also against ordinary (regular) negligence (carelessness); to try to get around them, you'd have to show gross negligence (extraordinary carelessness) or an intentional bad or wrongful act.The fact that a windstorm sent the barricade flying into you probably makes it impossible to hold them liable, since it would be very difficult to show that they should have anticipated an unusually powerful gust of wind, strong enough to pick up a barricade and send it careening into a person--or that someone would be out during such a severse storm. You would probably not be able to recovery money from them even if there was no waiver, since people are usually not responsible for weather-related injuries unless there were circumstances which would have put them on notice or guard of the possibility of harm; and given that there is a waiver and it would be very difficult to show gross negligence or intentional wrongful acts, it is even less likely that you would recover money.