While I can't speak to sewing machines, as they are far more likely to have metal bits floating around if there is also a mechanical issue, canned air is generally safe and good maintenance for computers if used properly. Keep the can upright, and the computer off and unplugged. I also press the power button with the PC unplugged to discharge capacitors before opening it up (not enough voltage to hurt you, but perhaps the machine) Trying to clean the computer while it is still running does allow for the potential to short something if the can lets out any liquid..... but is a bad idea for plenty of other reasons. Processor heatsinks will eventually clog to the point that they will insulate the processor and cause it to overheat and die if you don't clean them... and uness you have an professional air compressor of the quality you might paint a car with, (never even seen one in a computer shop) canned air is the only reasonable way to do it. Keep the can right side up, and the PC off, and you'll be good. Turn the can upside down, or PC running, and you might be tempting trouble.