On GMs the "BCM" has nothing to do with airbag deployment, it's all within the SDM (Sensing Diagnostic Module)The airbags are on top of the dash and aren't easy to trigger when working around them. There are multiple sensors that need to be tripped and the BCM needs to command deployment.
True, on modern airbag systems as used in the Volt the "remote" crash sensors such as those under the hood or on the rad support will not on their own trigger a deployment, however mishandling the SDM (located in the center console) while connected to the main airbag harness CAN trigger an inadvertent deployment. (and yes it has happened)
Most of the concern when "digging around" in the vicinity of an airbag is the potential of inadvertent deployment due to unknown wiring damage that might exist and manipulated during service. All the airbag needs is B+ on one circuit and GND on the other and a bag is out and in your face. (the SDM does not need to be involved) Yes it initially is delivered towards the windshield but is designed to deflect rearward off of the glass
The best defence when servicing areas in the proximity of the airbags, crash sensors, or SDM is to follow the GM service information steps to properly and when called upon to properly disable the airbag system completely (or zoned disabling). The take no prisoners approach is to shut the car off, remove all FOBs, and disconnect battery negative. Wait 2 minutes. Work away
Which is exactly what is listed as "STEP 1" in the blower motor replacement procedure, (due to the proximity) which shouldn't be ignored