Number Concentrations and Size Distributions of Chalk Particles Released During Writing and Wiping Activities in Classrooms in the Johannesburg Region

This study investigated the particle number concentrations (PNCs) and particle size distributions (PSDs) of chalk particles released during writing with dust‐free and normal chalkands when the chalkboard was wiped with different materials. A standard paragraph was written alongside a pie chart using dust‐free and normal chalk sticks, which was then erased with a chalkboard duster. A chalkboard duster, dry cloth, wet cloth and paper towels were also used to wipe the standard paragraph and pie chart written using dust‐free and normal chalk. The chalk particles were measured using a TSI 3330 optical particle sizer at a flow rate of 1 L/min. The mean PNC was numerically higher when writing with dust‐free chalk (2.13 ± 0.37 #/cm 3 ) than when writing with normal chalk (2.08 ± 0.35 #/cm 3 ); however, this difference was not statistically significant ( p = 0.70). The mean PNC was numerically higher when wiping a paragraph written with normal chalk (14.15 ± 1.15 #/cm 3 ) compared with dust‐free chalk (13.00 ± 1.32 #/cm 3 ); however, this difference was not statistically significant ( p = 0.14). Paper towels showed the highest PNC when wiping paragraphs written with dust‐free (18.68 ± 2.01 #/cm 3 ) and normal chalk (19.08 ± 1.27 #/cm 3 ), whereas a dry cloth recorded the lowest PNC for dust‐free (5.76 ± 0.51 #/cm 3 ) and normal chalk (5.22 ± 0.94 #/cm 3 ). Writing with and wiping off dust‐free and normal chalk mainly released fine particles (< 4.5 μ m), with peaks between 1.562 and 3.752 μ m. The various wiping materials also released fine particles, with most peaks occurring between 1.562 and 4.672 μ m for both dust‐free and normal chalk. Transitioning to alternative teaching tools, such as whiteboards or digital devices, is necessary to protect teachers′ health.