For a number of years, we have advised many of our clients to consider using large numbers and when possible, directional lettering (i.e. 1W for a front exterior door facing the West). This can help emergency responders arrive faster at the location at a school where they are needed when seconds count. This approach can also be helpful for daily wayfinding, helping visitors locate the appropriate door during a special event, or even for improving communications for maintenance requests. Our preference is for schools to place these numbers above the door on the exterior for outside way finding and low on the interior to help occupants evacuate in the event of a fire.
There are, however, times when external numbering could prove to be helpful to an aggressor. For example, during an assessment project for an independent school overseas, we advised a client not to utilize exterior door numbering. The school is at unusually high risk for terrorist attacks and is surrounded by a high privacy wall to make it harder for terrorists to conduct surveillance of the school. The campus is rather large with many buildings and can be difficult for someone who is not familiar with the layout to navigate. Due to unreliable law enforcement response in the region, we felt the benefits of this type of numbering were outweighed by the risks of terrorists being able to more rapidly locate victims in an attack on the campus. Trusted armed security personnel who would respond to an attack can utilize printed virtual tours and their familiarity with the campus for emergency wayfinding.
In the U.S., a far more common hazard involves situations where classroom and office numbers are placed on outside windows. This could allow someone coming to a school to attack or attempting to abduct a specific person to more easily locate a particular victim or group of victims. We suggest school and public safety officials weigh the advantages and disadvantages of this approach before marking individual rooms on the outside of the building.