one more thing though... no air bag will ever deploy unless you are sitting in the seat and have the seat belt on...
other than that I see no reason why would the airbag go off if the truck was hit from the side...
Usually as it is explained in the Owners manual - air bag would deploy if you are in the frontal collision and the truck is hit anywhere within 30 degrees off the center of the truck.
Here's what I copied from Wikipedia:
"Triggering conditions
Air bags are typically designed to deploy in frontal and near-frontal collisions, which are comparable to hitting a solid barrier at approximately 8 to 14 miles per hour (mph) (13 to 23 km/h). Roughly speaking, a 14 mph (23 km/h) barrier collision is equivalent to striking a parked car of similar size across the full front of each vehicle at about 28 mph (45 km/h). This is because the parked car absorbs some of the energy of the crash, and is pushed by the striking vehicle. Unlike crash tests into barriers, real-world crashes typically occur at angles, and the crash forces usually are not evenly distributed across the front of the vehicle. Consequently, the relative speed between a striking and struck vehicle required to deploy the air bag in a real-world crash can be much higher than an equivalent barrier crash.
Because air bag sensors measure deceleration, vehicle speed and damage are not good indicators of whether an air bag should have deployed. Occasionally, air bags can deploy due to the vehicle's undercarriage violently striking a low object protruding above the roadway surface. Despite the lack of visible front-end damage, high deceleration forces may occur in this type of crash, resulting in the deployment of the air bag.
The airbag sensor is a MEMS accelerometer, which is a small integrated circuit chip with integrated micromechanical elements. The microscopic mechanical element moves in response to rapid deceleration, and this motion causes a change in capacitance, which is detected by the electronics on the chip, which then sends a signal to fire the airbag. The most common MEMS accelerometer in use is the ADXL-50 by Analog Devices, but there are other MEMS manufacturers as well.
There was some work initially in mercury switches but they did not work very well. Before MEMS, the primary system used to deploy airbags was called a "rolamite". A rolamite is a mechanical device, consisting of a roller suspended within a tensioned band. As a result of the particular geometry and material properties used, the roller is free to translate with very little friction or hysteresis. This device was developed at Sandia National Laboratories. The rolamite and similar macro-mechanical devices were used in air bags until the mid-1990s when they were universally replaced with MEMS.
Most air bags are designed to automatically deploy in the event of a vehicle fire when temperatures reach 300 to 400 degrees Fahrenheit (150 to 200 °C). This safety feature helps to ensure that such temperatures do not cause an explosion of the inflator unit within the air bag module.
Today, airbag triggering algorithms are becoming much more complex. They try to reduce useless deployments (for example, at low speed, no shocks should trigger the airbag to help reduce damage to the car interior in conditions where the seat belt would be an adequate safety device) and to adapt the deployment speed to the crash conditions. The algorithms are considered as very valuable intellectual property. Experimental algorithms may take into account such factors as the weight of the occupant, the seat location, seatbelt use, and even attempt to determine if a baby seat is present."
