Each year, about 600 fires/explosions of freestanding gas grills occur nationally, with an average of 30 people injured. (see this article: http://www.townofbrookfield.com/Documents/Tidings/2002/Tidings%202nd.pdf) These numbers are fairly low, considering the number of outdoor gas grills in operation. These are the main precautions to avoid an accident:
1 Never use a grill within 10 feet of a building.
2 When you use a gas grill that has been idle for quite a while, check for blockages in the tubes from built-up grease or insects, and inspect the hoses for cracks or brittleness.
3 Make sure the hoses are not near any dripping grease or hot surfaces.
4 Do not store gas containers near the grill and do not smoke near it.
Using the proper sequence for starting the grill will prevent excess gas from accumulating inside the grill before it is ignited, thus avoiding a fire/explosion.
To start the grill, you should: open the lid, turn on the gas, turn the ignition burner to high, light the ignition, turn the second burner on if needed.
For more info, see: http://www.gasgrillsnow.com/GasGrillSafety.htm