Issues regarding air purging in the S&W ethylene plant

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I would like to ask the experts: In the design of S&W ethylene plants, pipelines are typically introduced after a gas-phase dryer, which is used for purging the plant during the initial startup phase. Propylene refrigeration compressors and ethylene heat-pump compressor systems are utilized to carry out tasks such as pipeline purging and drying. Such a setup also has a drawback: since the vapor dryer is located at the fourth-stage outlet of the pyrolysis gas compressor, if communication is not established properly during the purging of downstream equipment or if valves are opened and closed too quickly, it can lead to fluctuations in the flow rate at the compressor outlet, which in turn may cause compressor surging or even shutdown. During the preparation of the plant purging plan, it was proposed on several occasions to run temporary lines directly from the fifth-stage outlet line of the pyrolysis gas compressor to the ethylene plant, the propylene plant system, and even the propylene tower system, for use in the initial startup purging. They believe that using five stages for venting is more controllable compared to using four stages; it has less impact on the pyrolysis gas compressor and is more conducive to its stable operation. However, during the air operation of the pyrolysis gas compressor, could the temperature at the fifth-stage outlet be too high, given that it is used as the purge gas source for the refrigeration compressor? Is it not good for downstream system devices? Why is a five-stage air source not used during the purging of so many ethylene plants, whereas a four-stage air source from the cracking gas compressor is employed? I would appreciate your advice; thank you!