Melting Risks: Plastic Storage Materials in Fire

In preparation for our fire recovery workshops, we try to use a variety of storage materials in the mock museums we set up before a controlled burn. We stage plastic storage boxes, made from polypropylene (PP), and tyvek dust covers and artifact tags, made from polyethylene (PE), alongside storage enclosures made from archival board and muslin.  The view on the left shows one shelving unit pre-fire and before we placed clear PE sheeting around the unit as a dust cover. Note the tyvek dust cover on the uppermost rolled textile and tyvek tags hanging from objects.

Although plastic enclosures can offer an additional measure of disaster preparedness for certain scenarios, such as water and pests, they do not protect artifacts as well as other materials in the case of fire. The fire, which burned at about 350 degrees for 2 hours, blew off the PE sheeting from its clips around the shelving unit and left the plastic cover a melted, sooty mess on the floor. Tyvek responds to extreme heat by shrinking up like a shrinky dink and eventually darkening and sticking to the adjacent artifact. The image above shows the same textile in the pre-burn shelf view (above left) with the shrunken dark remnants of its tyvek cover after the fire. Conversely, the cotton twill tape ties are sooty but still intact.

post burn view

post burn view

Not all plastics in our “museum” setting responded in the same way. Placement and perhaps thickness of the materials affected the risk to the nearby artifacts. Remember that hot air rises, so the intensity of fire damage tends to be opposite from the intensity of flood damage. Tyvek tags on objects nearer the floor emerged from the burn building intact. In contrast, a tyvek tag on a hanging garment shrunk and darkened, though the tiny number is still surprisingly legible.

Note melted PP boxes on upper left and intact PP box on shelf below.

In previous controlled burns we have tested PP storage boxes with favorable results. Those same storage boxes made it through our recent BuncombeCounty burn well too. Two smaller PP boxes, made from thinner plastic, melted, though still not enough to harm the objects inside. Was it the placement or the varying thickness of the plastic boxes that caused the different outcomes?

Our controlled burns have taught us that plastic enclosures kept closer to the floor pose less melting risk than those at higher levels. Significantly, the closer to the floor, the greater the risk for flood and pest damage to artifacts. Also, proximity to floors and walls can increase RH fluctuations, and research has shown that plastic boxes help mitigate that collections risk. Might plastic enclosures be the best option for storage at lower levels in general?