3. Sometimes, changes can be classified as per their desirability. For example, the
burning of wood in fire place is
while the burning of trees in a
forest fire is
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dunha
Answers
Answer:
The reduction of ignitability and combustibility of wood products is based on chemical and physical means that have an effect on different stages of ignition and burning, for example:
heat induced changes of the internal structure of wood in molecular level;
physical and chemical processes of compounds produced in these changes, both inside the wood and in the gases formed above it;
transfer of heat in a wood product;
transfer of oxygen into reaction areas.
Following topics are covered in this section:
1. Ignition and combustion of wood
2. Fire performance of wood
2.1 Ignitability
2.2 Heat release and fire spread
2.3 Charring
2.4 Smoke production and toxicity
1. Ignition and combustion of wood
Many materials in our environment, including wood products, burn “indirectly” in the sense that the materials do not actually burn, but combustion takes place as a reaction between oxygen and the gases released from a material (an exception from this rule is the glowing combustion of charred wood where oxygen reacts directly with carbon). Under the influence of heat, wood produces easily substances that react eagerly with oxygen, leading to the high propensity of wood to ignite and burn.
Ignition and combustion of wood is mainly based on the pyrolysis (i.e. thermal decomposition) of cellulose and the reactions of pyrolysis products with each other and with gases in the air, mainly oxygen. When temperature increases, cellulose starts to pyrolyse. The decomposition products either remain inside the material or are released as gases. Gaseous substances react with each other and oxygen, releasing a large amount of heat that further induces pyrolysis and combustion reactions. Pyrolysis and burning processes are illustrated in Figure 1.
Answer:
Are u form ncert
Explanation:
this the question of NCERT