Post written by: Martin J. Morisky CPCU, ARM, ALCM, ARe
During the past few decades, there has been increased use of “sandwich panels” in construction. They are cheap, lightweight, easy to erect, hygienic and able to provide an excellent thermal barrier. While they do not start fires, they have been implicated in rapid fire spread caused by a hazardous operation.
What are “Sandwich Panels”?
A sandwich panel consists of a core of insulating material sandwiched between two layers of metal, usually steel or aluminum, bonded under pressure. Insulating material may be combustible or non-combustible. A list of materials used, from worst to best, and their combustibility are as follows:
- Expanded polystyrene or polyethylene (highly combustible)
- FRP or glass-reinforced polyester resin (combustible)
- Polyurethane or polyisocyanate (combustible)
- Glass fiber or mineral wool (non-combustible)
Why are they hazardous?
A building constructed of sandwich panels does not maintain its integrity in a fire and the panels may actually contribute to the fire spread. Polystyrene and polyethylene cores start to melt at approximately 200 F, which allows these plastics to flow and feed the fire like a flammable liquid. Polyurethane, polyisocyanate, and FRP ignite in a range of 650 F to 1000 F. All of these materials release a thick, black, sooty smoke when they burn. And all will burn, whether formulated with fire-retardant or not, under the right conditions. All buildings of this type of construction are rated as Frame (1) by the International Organization for Standardization. Buildings of this construction tend to collapse in a fire.
Panels that use glass fiber or mineral wool do not burn, but they do not hold up well in a fire and also tend to collapse. Buildings of this type of construction are rated as Non-combustible (3) by ISO.
Where are sandwich panels used?
Sandwich panels are prevalent in the food industry, cold storage warehouses, electronics and pharmaceuticals, but may be found almost anywhere.
How can one tell if a combustible or a non-combustible panel was used in building construction?
This is a tough question and even ISO inspectors have made mistakes. Short of cutting the panel open, the best and most accurate method is to obtain the name of the company that manufactured the panel and then consult their data sheets.
What steps can be taken to minimize fire loss in combustible sandwich panel construction?
- Hazardous processes that may be sources of ignition should be adequately protected and located away from the walls. Welding, cooking, forklift battery recharging and spray painting are examples of hazardous processes.
- All electrical passing through the walls or ceiling should be enclosed in metal conduit.
- Leave wide aisle spaces between storage and sandwich paneled walls.
- Interior walls should be of non-combustible construction to provide a degree of compartmentalization.
- Prevent forklift damage to any panels and promptly repair any damage that may occur.
- Combustible materials should not be stored along the outside walls of the building.
- Sprinkler protection adequate for the occupancy should be provided when a substantial portion of the building is constructed of combustible sandwich panels. NFPA guidelines require sprinkler protection for combustible construction unless the building is totally vacant.
Combustible sandwich panel construction is insurable, but protective safeguards must be followed to prevent a catastrophe.
For more information on sandwich panels see: FM Global, “Understanding the Hazard, Plastics in Construction”; Gen Re Facultative Matters, November 2004, “Questions and Answers about Composite Panels”; Association of British Insurers, May 2003, “Technical Briefing Fire Performance of Sandwich Panel Systems”; FM Global, Property Loss Prevention Data Sheets, “Plastics in Construction”.