The frequency of cleaning alone is not enough to determine whether a layer contains sufficient dust to be a risk. The rate of deposition of the dust has different effects, for example, a secondary grade of release with a high deposition rate may create a dangerous layer much more quickly than a primary grade with a lower deposition rate. Both the frequency of cleaning and the effectiveness of cleaning are important.

Thus, the presence and duration of a dust layer depends on:
– the grade of release from the source of the dust,
– the rate at which dust is deposited, and
– the effectiveness of housekeeping (cleaning).
Three levels of housekeeping can be described.
Good: Dust layers are kept to negligible thickness, or are non-existent, irrespective of the grade of release. In this case, the risk of the occurrence of explosive dust clouds from layers and the risk of fire due to layers has been removed.
Fair: Dust layers are not negligible but are short-lived (typically less than one shift). The dust is removed before any fire can start.
Poor: Dust layers are not negligible and persist for a long period of time (typically more than one shift). The fire risk and secondary explosion risk may be significant
Poor housekeeping combined with conditions that can create a dust cloud from a layer should be prevented. Any conditions that can create a dust cloud (for example, someone entering the room) shall be considered in the hazardous area classification.
NOTE When a planned level of housekeeping is not maintained, additional fire and explosion risks are created.
Cleaning important, a good preventive action. On the other side the hazardous conditions of any dust present user shall be aware of as well.
Keep up good work!

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