It is not the safety of the photographer but the safety of the camera at stake here. Some flashes use very high voltages in the trigger circuit that may be high enough to fry your camera’s circuit board. If you are temped to buy cheap flashes from garage sale or off eBay to expand your strobist arsenal, check this site first to make sure it is safe to use on your camera or other triggering devices’ hotshoe.
If the flash you are interested in is not listed, you can follow the instructions (scroll down until you see How to Check the Trigger Voltage) to measure it yourself. My Starblitz 200 DNX isn’t listed in there. The voltage on the sync terminal is ~11 volts. I put it on my Nikon D200 and it works just fine. According to Nikon D200 manual, the accessory shoe on the camera can support up to 250 volts.
Keywords: Flash photography, Strobist, Sync Voltage