The most important prevention step is to remain on groomed runs, resisting the urge to ski or snowboard through the trees during deep powder conditions, no matter how inviting the untracked powder looks.
If you do decide to venture off the groomed runs, remember:
It is critical to ski or ride with a partner who remains in visual contact* at all times.
Some of the deaths on mountains in North America which have occurred due to tree well incidents may have been avoided had:
It does NO GOOD for your safety if you are under the snow and your partner is waiting for you at the bottom of the lift. If you have any question about what a "timely manner" is to assist someone in a tree well, hold your breath now as you are reading this and the amount of time until you need air is approximately how much time your partner has to help get you out of danger. Other factors such as creating an air pocket or the nature of how you fall into the well may extend this critical timeframe.
*Visual contact means stopping and watching your partner descend at all times, then proceeding downhill while he or she watches you at all times. IF YOU LOSE VISUAL SIGHT OF YOUR PARTNER, YOU COULD LOSE YOUR FRIEND.
The same basic essentials as backcountry skiers or snowboarders: a transceiver, shovel, probe, and whistle.
If you are a skier, remove your pole straps before heading down a powder slope. Trapped skiers have difficulty removing the pole straps, which can hamper efforts to escape or clear an air space to breathe.
Hopefully, your partner will have seen what happened and will come to your rescue within minutes. If not, experts advise staying calm while waiting for assistance. Survival chances are improved if you maintain your air space. Over time, heat generated by your body, combined with your rocking motions, will compact the snow, and you may be able to work your way out.
Deep snow can be fun, but it can also be extremely dangerous. Follow these guidelines and remember, safety starts with you!