Airport, What would you want in your plan? Rescue of people involved in a trench collapse need both training and understanding as to the dangers to themselves and others, equipment to facilitate this etc. In addition each trench would likely to have it's own unique problems, depth, air quality, water, design? I would expect a policy with a robust SSoW to prevent such occurrences, monitor and check that this is actually being carried out and deal robustly any short cuts! Management plan as to should be done, as you indicate time is of the essence, especially with regards to informing the emergency services who are trained and equipped to carry this out without endangering others?