It's no problem. A spark is a phenomenon in which small particles are produced by colliding objects, absorbing the heat generated by the collision and burning. Due to the good thermal conductivity of copper, so that tools and objects friction or impact, the heat generated can be rapidly conducted open, so that copper can not reach the high temperature of the ignition point, another reason because copper itself is relatively soft, not easy to produce small metal particles, but also because copper is soft, iron will not produce small metal particles, so will not produce sparks.