Friday, 1 November 2013

Measurements of Dustiness - 'Hairy Arm' Test .... and Improvements !

Dust in bulk materials can have several and varied impacts on users and producers.

Impacts on the producer include:
  • Cost of wasted material.
  • Process time and equipment optimisation.
  • H&S related processing issues.
Cost to the user include:
  • Materials purchased that can be utilised.
  • Processing difficulties.
  • H&S related issues in handling.
So how exactly do you measure the dustiness of a bulk material ? 

I've seen methods used, for example with desiccant materials, where a QC operative assessment is to plunge an arm into the bulk container, remove it from the bulk and assess the amount of dust caught on the hairs of the arm ...... the 'Hairy Arm' test.

At FIL, we now offer an instrument DustView II which uses a 'drop test' for the bulk being investigated.  Originally developed in conjunction with a major manufacturer of fertilisers, a measured weight of material is placed in a small hopper and a valve opened rapidly to allow the material to drop down a tube, under gravity, impacting on a baseplate mounted inside a chamber below.  This chamber is monitored by an optics based dust monitoring system which fives an output based on obscuration / scattering of a light beam.  The level of scattering is dependent on the dust concentration released during the fall and impact of the process.

Other methods exist and although it is difficult to correlate different systems or link any measured values to explosability limits etc., as an indicator of dust levels and a quality control tool it has proved to be a quick and useful instrument for both manufacturers and users.

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