Little Pro on 2016-01-13 Views:  Update:2018-04-02

Viscosity is the measure of a liquid’s resistance to flow. There are two types of viscosity: Dynamic viscosity and Kinematic viscosity. You can often find it in the section 9 of a safety data sheet (SDS).

Dynamic Viscosity [Pa.s = 1 kg/m?s] is a measure of a liquid’s resistance to its shearing flows, where adjacent layers move parallel to each other with different speeds.

Kinematic Viscosity is a measure of the resistive flow of a fluid under the influence of gravity. The kinematic viscosity [m2/s] is the ratio between the dynamic viscosity [Pa.s = 1 kg/m?s] and the density of a fluid [kg/m3]. The SI unit of the kinematic viscosity is m2/s. Other units used include St and cSt.

1 St (Stoke) = 1 cm2/s = 10^(?4) m2/s

1 cSt (centiStoke) = 1 mm2/s = 10^(?6)m2/s

Water at 20 °C has a kinematic viscosity of about 1 cSt.

Regulatory Implications of Viscosity

Liquids with lower viscosity are generally more hazardous because they can spread more quickly. Usually, increased temperature reduces the viscosity of a liquid and makes it more hazardous.

Under GHS, a hydrocarbon shall be classified as aspiration toxicity hazard category 1 if its kinematic viscosity is less than 20.5mm2/s (20 cSts) at 40 °C .

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