Vapor suppression foams

While foam has traditionally been effective in the suppression of flammable and combustible liquid fires, its benefit as a suppressant of hazardous material vapors should not be underestimated. When used on spilled 

A number of factors contribute to the effectiveness of foam as a vapor-suppressant. These include the type of foam, its expansion ratio, its drainage time, the rate of application of the foam (gal per min/ft2), and its application density (gal/ft2). Chemical foams have become obsolete, with mechanical foams now being used worldwide. A mechanical foam that has recognized attributes for vapor suppression is aqueous film-forming foam (AFFF). It is a synthetic foam (as compared to protein foams) with a surfactant that is part fluorochemical and part hydrocarbon. It suppresses vapors by forming an aqueous film produced by draining its foam bubbles. 

Foams are categorized by their expansion ratio. Low-expansion foams have a ratio of 20 1 or less. The ratio of medium-expansion foam is 20 1 to 200 1 and for high-expansion foam it is 200 1 to 1000 1. AFFFs are typically low-expansion foams. 

Another characteristic of foam is the concentration in which it is used. A 3% foam concentrate is mixed at a ratio of 97 parts water to 3 parts foam concentrate. Similarly, a 6% foam concentrate is mixed at a ratio of 94 parts water to 6 parts foam concentrate. Another key consideration is the 25% drainage time—the time required for 25% of the foam s liquid to drain from the foam. This characteristic can be used to measure foam stability, and in combination with the expansion ratio, it can be used to determine how the thickness of the foam blanket will vary with time (NFPA 471, 1989). This dictates the rate at which foam will have to be added to the initial blanket to ensure continued mitigation effects. Second, the drainage time can be used to determine the water, both total quantity and rate, that will have to be dealt with to prevent the incident from becoming an environmental incident as well. 

When using foam as a vapor suppressant, the vapor pressure of the spilled material is important. That is to say, the higher the vapor pressure, the thicker the foam blanket should be. 

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Spills/Leaks Absorb spill with inert material (e.g., vermiculite, sand, or earth), then place in suitable container. Avoid runoff into storm sewers and ditches which lead to waterways. Clean up spills immediately, observing precautions in the Protective Equipment section. Remove all sources of ignition. Use a spark-proof tool. Provide ventilation. A vapor-suppressing foam may be used to reduce vapors. 

A vapor suppressing foam may be used to reduce vapors. 

SPILL CLEAN-UP use water spray to cool and disperse vapors apply vapor suppression foam to limit vaporization from liquid release if in liquid form, absorb as much as possible with materials such as dry earth or sand remove all ignition sources. 

SPILL CLEAN-UP ventilate area of leak or spill vapor suppressing foam may be used to reduce vapors absorb or cover liquids with non-combustible materials (e.g., dry earth, sand, vermiculite), and transfer to chemical waste containers use clean non-sparking tools to collect absorbed materials flush remaining spill with large amounts of water but not into confined spaces such as sewers due to possibility of explosion remove all sources of ignition (e.g., flares, sparks or flames). 

SPILL CLEAN-UP ventilate area of spill or leak stop flow of gas if possible if leak cannot be stopped, allow to empty in open air in a safe place use vapor-suppressing foam to blanket release remove all sources of ignition. 

A total of six tests was performed. Each involved transferring liquid chlorine from one or more 1-ton chlorine containers to the open pan. After the pool of liquid chlorine had stabilized, measurements were made of downwind concentration with no mitigation procedure applied. Then one of several different mitigation procedures was performed on the liquid pool. In the first and last tests, the only mitigation technique used was water spray nozzles to knock down the chlorine vapor cloud. In tests 2, 3, and 5, different vapor suppression foams were applied to the liquid pool surface in combination with water spray from the nozzle system and measurements were made of the downwind concentration to determine the effectiveness of the procedure. Test 4 used no foam but did use the water spray nozzles and portable water nozzles. 

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