By John W. Mittendorf
The last “Reading A Building” article covered one of the most dangerous types of building construction suppression personnel can encounter on the fireground – fascias. Although any type of construction exposed to fire can present a significant hazard, specific types of construction are capable (and willing) to pose unique hazards. Such is the case with unreinforced masonry construction (URM). Fortunately, this type of construction is often easily recognizable. You can expect buildings of this type to present a specific hazard when exposed to fire – collapse.
Prior to 1933, brick buildings featured the following characteristics:
- Mortar consisting of sand and lime only;
- A lack of rebar;
- Exterior walls about 13″ thick and tapering vertically upward (reducing in thickness);
- Parapet walls (which can often be of a noteworthy height) around the perimeter of a roof;
- Floor and roof joists that were “let” (resting in a cavity) into the exterior walls; and
- Roof and floor joists that were “fire cut” (ends are cut at an angle) so they would pull away from a wall and fall into the interior of a building without collapsing the exterior walls.
After the disastrous Long Beach, CA earthquake in 1933, building codes were revised to provide enhanced earthquake safety for new masonry buildings. Simultaneously, it also became apparent that these buildings were prone to collapse during fire conditions. As a result, the following revisions were implemented for new masonry construction:
- Cement to be used in the mortar;
- Steel rebar to be used;
- Exterior walls to be at least nine inches thick; and
- All joist and rafters to be anchored to exterior walls. This was normally accomplished by bolting a ledger board to a wall and attaching the joist/rafter to the ledger via a metal hanger.
After the Tehachapi, CA earthquake in 1959, many building codes (applied to masonry construction, and specifically URM construction) were modified (including some retrofits) as follows:
- Four to six inch concrete “cap” on top of parapets along public walkways and exits;
- Parapet could be no more than 16″ high (including the “cap”);
- Rafters and joists had to be anchored to exterior walls with a steel anchor bar or rod.
The Sylmar, CA earthquake of 1971 further emphasized the need for additional modifications to URM buildings. These modifications were primarily retroactive corrections adopted in California and partially or completely adopted by states outside California. These modifications were primarily designed to prevent exterior walls from collapsing outwardly by stabilizing a URM building by:
- Anchoring walls to floor and roof systems; and
- Strengthening roof construction (metal straps, etc).
With this brief history of URM modifications, one would think these buildings have been adequately strengthened to withstand the effects of earthquakes – and for our discussion, the effects of fire. However, this isn’t the case. Some of the aforementioned modifications have significantly increased the hazard of collapse to fireground personnel. The next article will explore specific hazards and how to identify URM buildings.
John W. Mittendorf joined the Los Angeles City (CA) Fire Department (LAFD) in 1963, rising to the rank of captain II, task force commander. In 1981, he was promoted to battalion chief and in the year following became the commander of the In-Service Training Section. In 1993, he retired from LAFD after 30 years of service. Mittendorf has been a member of the National Fire Protection Research Foundation on Engineered Lightweight Construction Technical Adisory Committee. He has provided training programs for the National Fire Academy in Emmitsburg, Maryland; the University of California at Los Angeles; and the British Fire Academy at Morton-in-Marsh, England. He is a member of the editorial advisory board of Fire Engineering and author of the books Truck Company Operations (Fire Engineering, 1998) and Facing the Promotional Interview (Fire Engineering, 2003).