Yes, it is safe to power nixie tubes all the time, the power consumption is below 1W per tube, they stay at room temperature. Our clocks are powered from power adaptor which is able to deliver only 24W, in case of short-circuit of any kind in the clock/tube, the power adaptor cuts off the power. No risk of setting surroundings on fire. Another safety feature is a PTC fuse in the clock itself, it also cuts off power in case of short.