IRSST - Institut de recherche Robert-Sauvé en santé et en sécurité du travail

Characterization of dusts in traditional bakeries


Several studies have concluded that bakers exposed to flour dust face the risk of being sensitized and of developing respiratory symptoms, and even occupational asthma (OA). Others report an increase in the risk of flour sensitization at levels of 2 mg/m3 even though there is a prevalence of sensitization of bakers exposed to 1 mg/m3 of flour dust. According to recent studies, workers in industrial or artisan bakeries could be exposed to as much as 7.8 mg/m3, and those in the milling industry to as high as 16 mg/m3. The majority of the studies report levels expressed as an inhalable fraction (Fi) of the dust.

The aim of the present study is to characterize the dusts in the air of artisan bakeries in terms of total dusts (Dt), the inhalable fraction (Fi) and respirable fraction (Fr), and to collect data on the particle size of the flour dusts generated during operations using flour.

The reported results correspond to two tasks where flour is handled by bakers: 11 series of samples at dough mixing/weighing, and 13 at the shaping/rounding table, where the flour is dusted. Fixed station sampling covered the total duration of the operations at each of the two stations. The median concentration at the mixing station was 4.9 mg/m3 in Dt (range < 0.03-17 mg/m3) and 8.0 mg/m3 in Fi (0.2-19 mg/m3), and at the table workstation it was 2.4 mg/m3 in Dt (< 0.03- 8.7 mg/m3) and 3.8 mg/m3 in Fi (0.2-9.2 mg/m3). The mass median aerodynamic diameter (MMAD) of the dust collected at the mixing station and at the table was approximately 23 µm.

The direct reading instrument used also linked the high concentration peaks to the different tasks performed. The small difference between the results of the duplicates of Fi adds to the method's analytical validation data in terms of the precision related to sampling and field manipulations. This fact demonstrates that the sampling and analytical method using an IOM sampler is applicable in the workplace for evaluating inhalable fraction dusts.

The average ratio of Fi to Dt is 1.6, with a standard deviation of 0.3, for the environmental measurements as well as for the impingers. It shows that the relationship is relatively constant in artisan bakeries, regardless of the workstation. Work practices differ from one baker to another, in the mixer startup speed, in pouring flour into water and vice versa, in the amount of flour used for flouring, etc. The median concentrations suggest that the mixing station is a more likely risk for flour dust exposure. A paired t test shows that the measured concentrations at the mixer are significantly different from those at the table.

The estimated exposure values for fixed stations, expressed as Dt, seem to be lower than the reference values of 10 mg/m3 for the dusts not otherwise classified (DNOC), but several are above concentrations that can cause lung sensitization according to the consulted literature. The main exposure risk factors in an artisan bakery are the total amount of flour used, the type of flour, the number of mixers in operation, the mixer's cover, and the work practices.

Additional Information

Category: Research Report
Research Project: 0099-8270
Online since: August 15, 2011
Format: Text