The influence of plastics in high piled storage – Part 3
Many modern products are constructed from a variety of constituents ranging from natural to synthetic elements. The vast number of potential combinations of wood, ceramic, metal, paper, leather, plastics and other materials barely can be imagined.
Likewise, many of these components are of little fire protection consequence when they have limited or no combustibility. The fire protection industry has more than a century of empirical evidence on methods to contain or suppress fires in these specific storage arrays. Fire sprinkler systems remain the most reliable protection means.
The increased use of petroleum-based and other plastics, however, has increased the fire hazard and consequent fire protection challenge. Some synthetics, especially Group A plastics, contain substantial latent heat potential and burn with high heat release rates that can overpower fire sprinkler systems. Research constantly is underway to find reliable, cost-effective solutions.
The fire code official and fire protection designer face a particular challenge when the commodity consists of a mixed amount of materials and Group A plastics in the product or packaging. The amount and form of Group A plastics ultimately can affect classification that changes a commodity from Class I-III to Class IV or even high hazard. The increased hazard class can severely affect the fire sprinkler system design.
To address the hazards with some amount of Group A plastics, International Fire Code (IFC) provides a graph to help classify the product and packaging into an appropriate commodity classification. (FM Global Property Loss Prevention Data Sheet 8-1 “Commodity Classification” provides an excellent explanation of the classification process. The data sheet can be downloaded free from http://www.fmglobal.com/research-and-resources/fm-global-data-sheets.)
Mixed Commodity Classification
Figure 1 is copied from IFC Chapter 32. It is used to determine the classification for commodities that may include some amount of Group A plastics.
Mixed Commodity Classification Graph for Group A Plastics
The graph has three axes that are important to classification:
- Left vertical: percent by volume of expanded plastics, ranging from 0 to about 32%,
- Right vertical: percent by weight of expanded plastics, ranging from 0 to about 9.25%, and,
- Horizontal: percent by weight of unexpanded plastics, ranging from 0 to 25%.
Class I, II or III commodities comprising less than 10% Group A expanded plastics by volume or less than 10% unexpanded plastics by weight can retain their original classification due to the small amount of Group A plastics. The grey area represents the range of Group A plastics that can cause a commodity to be considered a Class IV product, and anything to the right or above the grey area will qualify as a high hazard commodity.
To understand how the graph works, imagine a single thickness cardboard box filled with empty 750 ml wine bottles separated from one another single thickness dividers. The bottle manufacturer installs dividers to prevent breakage. According to the guidance in IFC Chapter 32, this most likely would qualify as a low-hazard Class I commodity and warehouse fire protection requirements would be relatively simple.
Now, imagine the bottle manufacturer receives numerous complaints from vintners that a substantial portion of the bottles are cracked or broken upon arrival at the winery. Not wanting to lose business, the bottle manufacturer explores packaging alternatives and learns that expanded polystyrene plastic dividers will reduce breakage by a substantial amount while not increasing packaging and shipping costs. Eventually, the expanded plastic dividers fill 15% of each box by volume.
Using Figure 1, the fire code official can determine that from 10 to 25% of Group A plastic in an otherwise Class I through III commodity will result in that commodity being group in the Class IV category. This can have a significant effect on the fire protection system design, while the bottle manufacturer may be unaware that the change has created a challenge.
Other products that contain mixed expanded and unexpanded Group A plastic can be classified by using both axes of Figure 1. Look at Figure 2, an innocuous appearing single unit thickness cardboard box. When the box is opened (Figure 2-A), it reveals a mixed load of expanded and unexpanded Group A plastics in the form of model railroad scenery packaging and packing “peanuts”. To determine the eventual commodity classification, one would have to compute the weight and or volume of both plastics.
While this is an extremely limited example, it turns out to be a good way to illustrate the use of Figure 1. The percent by weight of Group A unexpanded plastic (the clear plastic display windows) in this box is less than 5%. The percent by weight of expanded plastics (the packing peanuts) is about 6% with the cardboard box and the model railroad scenery making up the weight balance of the entire package.
Looking at the bottom axis of Figure 1 (percent by weight of unexpanded Group A plastic), this package would be at the far left: less than 5%. On the right vertical axis (percent by weight of expanded Group A plastic), find the 6% value. The intersecting point of the unexpanded plastic (5%) and the expanded plastic (6%) falls in the greyed area, making this box a Class IV commodity.
Normally, the code official should not have to do these calculations: it should be the owner, shipper or warehouse operators’ responsibility. The person doing the calculations should provide the plastic data and arithmetic for the code official to review and approve.
Also note that both formulas include the weight or volume of the materials handling feature, the pallet. Modern warehousing methods and recycling programs make high- and low-density plastic pallets an important part of the unit load. (The effect of plastic pallets will be covered in a subsequent article).
To determine the percent
by volume, use Formula 1:
Percent by volume = Volume of plastic in pallet load
Total volume of pallet load, including pallet
To determine the percent by weight, use Formula 2:
Percent by weight = Weight of plastic in pallet load
Total weight of pallet load, including pallet
Why Does It Matter?
The concern about various amounts of Group A plastics in commodities begs the question “Why does it matter?” The answer lies in both fire protection and economics.
First, when they are designed, fire sprinkler systems are matched to the hazard they are protecting: water supplies, pipe size, pipe layouts and sprinklers are arranged based on the heat of combustion and heat release rate of the material in storage. If the stored materials change and become more hazardous, the fire protection system should change as well. A fire sprinkler system designed to protect cardboard boxes with glass bottles inside cannot be expected to protect commodities that are substantially more hazardous. Adding Group A plastics to existing packaging may create a situation where the sprinkler system cannot control or suppress a fire, especially in high-challenge rack storage or solid pile arrays.
The economic factor corresponds to the fact the warehouse owner or operator does not want to spend more to protect the facility than is absolutely necessary. A sprinkler system designed to protect glass bottles likely costs significantly less than one for Class IV or high-hazard categories that need greater water supplies, larger and more closely spaced sprinklers and, in some cases, fire pump assemblies to deliver the needed pressures for fire control.
Plastics of all kinds can influence the fire behavior of commodities in various storage arrays. Because of their latent heat of combustion and heat release rate, Group A plastics are considered especially challenging in expanded and unexpanded forms.
Code officials, warehouse owners and operators, product manufacturers and shippers all should be aware of the hazards associated with Group A plastics in stored commodities and be prepared to take steps to protect them from unwanted fires.
For more information, go to codes.iccsafe.org
1. Unlike rigid plastics, expanded or foamed plastics are injected with air to increase their volume. Styrofoam® packing “peanuts” are an example of expanded plastics.