Whether the EC replies or not:
SSMA s62 part 2
(1) An owners corporation must properly maintain and keep in a state of good and serviceable repair the common property and any personal property vested in the owners corporation.
(2) An owners corporation must renew or replace any fixtures or fittings comprised in the common property and any personal property vested in the owners corporation.
You have made the EC aware in writing of a common property defect which is clearly a health and safety risk to lot owners and visitors. If committee members were more aware of possible unrestricted liability for harm resulting from their failure to act on this issue (tort of negligence) it would be brave of them to ignore their personal liability. Remind EC members, individually and jointly, in writing, documenting your evidence of delayed access by emergency services and request that this design defect is repaired forthwith.
I agree with Jimmy T's suggestion to table your letter at the next GM with a motion to repair/rectify the defect