They aren't allowed and never have been. Chainsaws work on a different principle to the spinners in the arena. Chain saw takes lots of little bites and so a fabric can jam it up. Spinners generally unleash energy in a single large impact. Your chainsaw trousers would be useless to absorb it.

Look into thick pieces of wood if you want to absorb the energy from a spinner whilst still fighting on. 2 to 3 inch thick plus.