Do a little studying of the Lapeyre Stairs alternating tread stairs.
https://www.lapeyrestair.com/product...-tread-stairs/

Before retirement, I was an engineer in the water/wastewater industry designing treatment plants all over the country. Our architects used the Lapeyre stairs in many plants where space was limited. They called them modified ships ladders. The manufacturer provided training for all the operators on the proper way to use the ladders safely. The ladders proved quite effective.