One is to evenly apply layers of intumescent paint bringing the total coating to the required thickness. If the steel is pre-primed then the intumescent paint can be directly applied. If there is any rust present then a rust kill/converter needs to be applied followed by a primer (red ox is usually used) before the intumescent paint can be correctly applied.
The other, is to use a tested fire board system. This system is commonly used on the likes of I beams as it is a quick, effective and aesthetically suitable option.
Either system can sustain a rating of up to 2 hours