A safety interlock system for an arc welder is described. The safety interlock system is interfaced with and turns on the arc welder in response to a user pressing a button 15. There may be an optional delay from when the user presses the button until when the arc welder is turned on. The safety interlock system maintains the arc welder operative for a predetermined period of time within which time an arc must be struck. The safety interlock system has a latching circuit 29 responsive to a parameter indicative of a welding operation underway, and will maintain the arc welder operative until the parameter ceases. Once the parameter ceases or if an arc is not struck within the predetermined period of time, the safety interlock system turns off the arc welder.