"Protecting the means of escape” using suppression means ensuring that survivable conditions are kept throughout the escape route.
Traditionally, guidance documents relied only on compartmentation, i.e. passive fire protection measures such as walls, fire doors, and door closers to ensure a fire would be contained only within the room where it started, keeping the escape route detached from the risk. It is assumed that a) the corridor would not be the location of the fire, they would be “sterile”, and b) that the “protected corridor” designed through the property would be free of smoke and heat from a fire in another room (because fire doors would be closed).
Fire suppression to protect the escape route should be in all the rooms not separated from the escape route by fire doors or walls, where the large fire loads are present, as opposed to the “sterile” corridors when used as a compensatory measure. Paraphrasing David Purser CBE: suppression should "address the fire rather than the escape route itself, protecting the escape route by taking the energy out of the fire".