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Polyurethane synthesis, wherein the urethane groups −NH−(C=O)−O− link the molecular units A kitchen sponge made of polyurethane foam . Polyurethane (/ ˌ p ɒ l i ˈ jʊər ə ˌ θ eɪ n,-j ʊəˈr ɛ θ eɪ n /; [1] often abbreviated PUR and PU) refers to a class of polymers composed of organic units joined by carbamate (urethane) links.
It has an explosive limit between 7.3% and 62% by volume in air, indicating a wide flammable range, which contributes to its high fire and explosion risk. With a vapor density of 2.1 (heavier than air) and a specific gravity of 1.14, nitromethane is a colorless, oily liquid that is slightly soluble in water but miscible with alcohol and ether.
For example, in the United States flammable liquids, by definition, have a flash point below 100 °F (38 °C)—where combustible liquids have a flash point above 100 °F (38 °C). Flammable solids are solids that are readily combustible, or may cause or contribute to fire through friction.
Chemical foam is a stable solution of small bubbles containing carbon dioxide with lower density than oil or water, and exhibits persistence for covering flat surfaces. Because it is lighter than the burning liquid, it flows freely over the liquid surface and extinguishes the fire by a smothering (removal/prevention of oxygen) action.
The stacking of the bubblets is similar to aspirated fire fighting foam or compressed air foam systems, except that bubblets are water filled, whereas foam bubbles are only filled with air. Due to the high specific heat of water, it requires more energy to raise the temperature of water than air. Therefore, water-filled bubblets will absorb ...
Due to the closed-cell nature of rigid polyurethane foams, PUR insulation has minimal water absorption, which coupled with an appropriate cover, makes it a particularly suitable in applications where bacterial growth is a concern. Polyurethane insulation is suitable for insulating pipes with surface temperatures ranging from -196°C to 148°C. [7]
As these chemicals are soluble in liquids-either water or dry cleaning fluid, these fabrics must be dry-cleaned with a non-liquid cleaning agent. [citation needed] The flame retardants work by coating the flammable fabrics with a mineral based barrier, preventing fire from reaching the fibres.
A flammable liquid is a liquid which can be easily ignited in air at ambient temperatures, i.e. it has a flash point at or below nominal threshold temperatures defined by a number of national and international standards organisations.