The picture above shows a locking bar that was installed up-side-down (note the "Lift Up" text):
The locking bar is pinned in place by TWO hairpin cotter pins (one visible at each end).
And the right leaf has a dead-bolt that pins into the floor at the bottom (which probably would not be visible should a crowd of people rush the door)
Additionally, the signage applied to the door should be worded:
NOTICE: This door shall remain unlocked during occupancy.