The past few decades have seen a resurgence of urban redevelopment that has prompted the adaptive reuse of century old buildings and warehouses into multi-unit residences. While such urban renewal projects offer new life to old neighborhoods, city planners are challenged in how to apply modern building codes to such retrofitted structures to ensure resident safety.
ESi encountered such in a case involving a century old building that had been converted to residences primarily occupied by students attending a nearby city college. Unfortunately, while several students were utilizing the building’s fourth floor fire escape as an evening gather space, the vintage steel structure broke away from its supporting masonry wall and tragically killed one student while seriously injuring two others.
ESi was retained to investigate material related aspects of the fire escape collapse.
Our Approach
ESi performed a site inspection of the building four months after the incident. The top-most fire escape platform steel angle iron cross support was connected to the building wall with two bolts embedded in the masonry just below a door sill. Two angled struts also supported the outboard portion of the platform and were embedded in wall masonry a couple of feet below the upper platform bolted wall attachments. During the site inspection, the remnants of the bolts were observed buried in the wall and had corroded to conical tips at their outboard separated extents. Fresh masonry fractures were documented around the original platform attachment points. Aged, flaked rusted metal was observed adhering to the building masonry where the platform angle iron support was originally resting against it.
Pieces of detached masonry grout as well as the two detached bolt portions had been previously found on the ground and retrieved from the scene. ESi performed a lab-based inspection of these pieces. Visual and optical microscopic examination of the bolt remnants revealed they were heavily corroded, and like their formerly attached remnant masonry buried pieces, also exhibited narrow conical tips where they had detached. Attempts to clean the bolt remnants failed to remove the adhering corrosion product. The heavy corrosion scale prevented examination of the original metal fracture surface using scanning electron microscopy.
One of the remnant bolts was axially cross sectioned through its conical tip and mounted for metallographic examination which confirmed the presence of long-term, heavy oxide scale on the surface. The microstructure contained steel phases ferrite/pearlite consistent with a low strength, high ductility, normalized steel bolt. Importantly no evidence of grain flow was observed near and adjacent to the conical tip confirming the bolt had been corroded completely through well before the collapse.
One of the retrieved masonry grout pieces exhibited the partial imprint matching one of the bolt remnant’s end, attached nut and washer, confirming this bolt was covered with grout prior to the collapse.
Services Utilized
Expertise Utilized
The Outcome
In the absence of the bolts’ retention capability, the platform remained tenuously attached to the building wall by vertical support from a narrow edge of cornice stone, railing attachment and adhering masonry grout that had been plastered over the platform angle iron and bolts. The completely corrode through condition of the two retention bolts was not visible to external visual inspection nor was there any evidence of looseness and impending collapse.
The fire escape was subject to annual visual and load test inspections by the city, and it had passed its most recent inspection.
This tragic accident prompted a critical review of inspection and testing requirements for such aged fire escapes.
