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TRANSOM WINDOWS: An often forgotten modern fire behavior danger lurks in Legacy constructed buildings

If you attended an older school like I did growing up I guarantee your teacher or even you yourself performed a ventilation technique and didn’t even know it when you opened them, what am I talking about? It’s the transom window and their effect on your operations in legacy buildings need be taken into consideration, especially with all that has been recently disseminated to our fire service in regards to ventilation and fire behavior.

A transom window is a window above a door that is usually hinged to a horizontal crosspiece over the door to provide cross-ventilation while maintaining security and privacy (due to their small size and height above floor level) they were a common feature of office buildings and apartments before air conditioning became common. These windows are usually still single pane glass and can fail under fire conditions and worse yet their presence could be hidden by drop ceilings or wood coverings as an energy conservation method or for aesthetic reasons.  

Many times these windows may also be painted over or covered with some type of decorative material hiding their existence. Failing to identify the presence of a transom window can create problems, such as allowing high heat and smoke to exit into common areas. Although employing the correct strategy of controlling the door and flow path, a firefighter may miss this problematic detail. The consequences of this error will critically affect life safety of both firefighters, civilian in unprotected areas and allow for rapid fire spread which is already a major concern in Type III ordinary constructed occupancies.

Our education rightfully so, speaks of the modern fire environment and I believe, many times mistakenly leads many younger firefighters into thinking that every environment will not only be of modern combustibles with faster heat release rates than seen with legacy furnishings but also modern construction and the hazards associated with. In the coming years I hope some emphasis is placed on the modern fire environment in legacy buildings.

If you are aware of their existence and believe you have an active fire you must consider rapidly changing conditions caused by their possible failure, another reason to go in with a charged hoseline and a crew ready to attack fire!

The failure of transom windows contributed to a rapid fire spread at the Our Lady of Angels fire which occurred in Chicago on December 1st 1958 and tragically took the lives of three teachers and 92 students.  As noted in several after action reports, when this tragic fire was discovered many of the teachers closed their doors in an attempt to “shelter in place” and protect their students; the fire, which began in the basement and raced up the open stairwell feeding off the combustible interior finish of the hallways intensified and caused the transoms to break thus allowing high heat and smoke into the classrooms.


A good engine company officer at 0300 may not notice them under fire conditions when stretching in on an ordinary constructed apartment building but the smart company officer will recognize and familiarize their crew prior to the incident at a walk through, building inspection, or medical call. If you protect an older “legacy” area, it is highly likely you have these windows educate yourself and when studying current fire behavior don’t forget to incorporate their unique hazards to your members.


Stay Safe

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