Yes, you can open the door. We recommend opening quickly and infrequently.
Guidelines from UK Power Networks state that in the event of a power cut or when power has been turned off, food is safe in your fridge for 4-6 hours with the door closed and a full freezer can last up to 24 hours.
As Equivents last up to 1 hour maximum, it is safe to open your fridge door quickly to minimise the amount of warm air you let in. We would also suggest minimising the number of times that you open a fridge/freezer door during an Equivent.