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Description of key information

Flammability [dichloro(dimethyl)silane]: Highly flammable

Key value for chemical safety assessment

highly flammable

Additional information

The flammability of liquids is assessed on the basis of flash point.

There is no indication on the basis of structure and experience in handling and use that the substance is pyrophoric (flammable in contact with air) or flammable in contact with water.

Therefore, in accordance with Section 1 of REACH Annex XI, there is no need to conduct further flammability testing. In secondary sources to which reliability could not be assigned, lower and upper flammability limits in air at 25°C and 101 kPa of 3.4% and >9.5% by volume respectively were reported for the substance. Similarly, lower explosion limit of 3.1% and upper explosion limit of 40% were also reported.

Justification for classification or non-classification

The substance is classified as Flammable Liquid Category 2 (H225: Highly flammable liquid and vapour) according to EC Regulation 1272/2008. This is on the basis of a flash point of 1°C and a measured boiling point of 70.2°C.

Thus, there is a risk of fire if dichloro(dimethyl)silane is stored or handled incorrectly. Vapours may form in closed rooms with air mixtures, leading to explosion in the presence of sources of ignition, even in empty, uncleaned vessels. The vapour is heavier than air, therefore, flammable mixtures may form close to ground level. The substance is a non-conductor and, therefore, can accumulate static electrical charges when processed, handled or dispensed.

Chlorosilanes burn in a manner similar to burning hydrocarbons; producing large amounts of grey or black smoke. However, the quantity of heat produced by burning chlorosilanes is typically lower than that of most flammable hydrocarbons. Hydrogen chloride, oxides of silicon, oxides of carbon, and various other combustion by-products may be evolved (CES 2003).

If water is used in fire-fighting, significant amounts of corrosive vapours may be produced (see Section 6.4 for reactivity of the substance with water). Much of the experience fighting chlorosilane fires has been obtained either in a controlled test environment or on a relatively small scale. Experience with fighting chlorosilane fires on a large scale has been extremely limited. Actual fire conditions could present unique and challenging fire-fighting situations, and fire extinguishing in some cases could be extremely difficult (CES 2003).

Therefore, as with all flammable liquids, fire prevention is extremely important when using or storing chlorosilanes. This not only includes the provision of measures to minimise the potential for ignition, but also the design of equipment and facilities to prevent the release of chlorosilanes. No special fire prevention measures other than those typically recommended for flammable liquids are necessary when storing or using chlorosilanes (CES 2003). Risk management measures intended to mitigate the hazard posed by the flammability of the substance are included in Section 10 of the CSR.