I reckon I'm probably qualified to add my 2 cents on this subject. I have a soda blasting business. I use food grade bicarbonate soda which is run through a purpose built machine which is worth a small fortune. The soda is slightly alkaline so yes it will kill off your grass if left on it. It also very dusty although is not harmfull. However you wouldn't want to breathe in too much so a mask and eye protection should always be worn. I do a lot of automotive paint removal on steel, fibreglass and aluminum which would be about 80% of my business. This ranges from car, truck and trailer restorations. The rest is stripping paint from antique furniture both wood and steel as well as motorbike frames, engine parts etc etc. The process is much softer than garnet & sand as it doesn't harm the base stucture or cause flash rusting or damage rubber, glass, chrome, seals etc. As mentioned it needs a substantial amount of the soda to do the job sucessfully as well as a good aircompressor supplying a large constant air supply. Moisture is your worst enemy as clogging in the line causes all sorts of headaches. Using one of these small suction type systems may be fine for a small job ocassionally but they certainly won't be up to the bigger tasks. To put it in prespective my unit is a 4.5l John Deere deisel engine running a 210cfm compressor with air tank, filters, condensor and a soda pot with a blast hose attached. I use a 25kg bag of soda per 1/2 hr at 90psi for say on a motorbike frame. It takes approx 40 minutes to completely strip a MX frame back to bare metal. Once used the soda is reduced to a talcum like powder with very little abrasive properties so re-use for the same purpose isn't usually viable. There are no issues with sparks using bicarbonate soda however it is recommended that the machine be grounded to prevent electrostatic discharge near anything flammable as a precaution
Prior to re-painting or powder coating the blasted item will require a thorough wash to remove the residual soda. If you don't you will be in a world of trouble with adhesion issues. The Vaqua (vapour) blasting process of using glass bead suspended in water at high pressure gives excellent results on alloy parts of cars and motobikes. It gives a semi polished finish. I have one of these units on order which will hopefully compliment the business. This process has already been covered elsewhere on this site by Firko and worth a read. Hopefully this info has been of some value. Cheers Dave