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Auto flammability

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auto-ignition temperature (liquids)
Data waiving:
study scientifically not necessary / other information available
Justification for data waiving:
the study does not need to be conducted because the substance is a liquid non flammable in air, e.g. no flash point up to 200°C
relative self-ignition temperature (solids)
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
supporting study
Justification for type of information:
The source substance is the racemic form of the target substance d-tetramethrin. Tetramethrin does consist of 50% d- and l-form, and both do exist as cis and trans isomers. Hence, the target substance does consist of d-cis-tetramethrin, d-trans-tetramethrin, l-cis-tetramethrin and l-trans-tetramethrin, whereas the target substance only contains the first two (i.e. d-cis-tetramethrin, d-trans-tetramethrin).
Both, the source as well as the target substance, do have a cis/trans ratio of approximately 1/4 and obviously do share same molecular mass and other properties. Thus, the source substance by definition does contain 50% of the d-form and the l-form is not expected to be significantly different with respect to its flammability behaviour. However, as the racemic form is solid, compared with the d-tetramethrin being liquid at 20 °C, the study performed using the racemic form to determine self-ignition temperature was performed up to 75 °C only, which is the melting point of the racemic form. No self-ignition was observed up to this temperature. However, the racemic substance was also assessed for flammability properties and treated with the flame of a Bunsen burner, not showing signs of ignition. Thus, it can be reasonably assumed that the liquid d-tetramethrin will not be critical with respect to auto-ignition temperature.
The d-tetramethrin with a purity > 80 % does contain its corresponding l-form as an impurity in the range of < 7%, other impurities from the manufacturing process are individually below 1% (w/w) each. The source substance that has been tested was having a purity of approx. 98% as tetramethrin with a cis/trans ratio of 1/4 and a d-form/l-form ratio of ~50/50.
Source and Target substance do share identical structure and molecular weight, only differentiating by the fact that the source substance is a racemic mixture, whereas the target substance represents almost pure d-form. Thus, physico-chemical parameters, not being affected significantly by stereochemistry, are fully comparable, thus justifying using available data on flammability and auto-ignition properties on the racemic form for supportive read-across to the d-enantiomer.
Composition comparison
D-tetramethrin (target) tetramethrin (source)
D-trans tetramethrin 70 - 80% 40 – 50%
D-cis tetramethrin 10 - 20% 7 – 11 %
L-trans tetramethrin 0 – 5% 35 – 40%
L-cis tetramethrin 0 – 2% 7 – 11%
Reason / purpose:
read-across source
Reason / purpose:
read-across source
Remarks on result:
no self ignition observed under the test conditions

Description of key information

The study to determine autoignition temperature does not need to be conducted because the substance is a liquid non-flammable in air, e.g. no flash point up to 200 °C. Although the flash point determination was waived, results from the racemic mixture, tested for flammable solids (see supporting study) showed, that the substance could not be ignited with a Bunsen burner flame. Thus, the study for flash point determination is scientifically not necessary, although the d-tetramethrin is liquid at ambient temperature.

Furthermore, the racemic mixture was tested for relative self-ignition temperature and did not show any self-ignition up to its melting point of 75 °C, supporting the assessment that auto-ignition is not a critical property of the substance.

Key value for chemical safety assessment

Additional information