Breathing rate. The exposure dose D, with dimension [bacteria s/m3], must be scaled by the breathing rate of an individual þ, with dimension [m3/s], to provide an estimate of the number of bacteria inhaled. This is called the inhaled dose. An individual’s breathing rate is usually assumed not to change while a packet of air passes over him or her. The breathing rate of an average person may be assumed to be 0.012 metres cubed per minute as a baseline (light intensity activity) but this may increase or decrease depending on age, activity and stress levels (see Table 6.2 (Xxxx, Xxxxxxxx et al. 2011)). Sedentary or resting travellers would be more likely to have breathing rates of 0.004 or 0.005 metres cubed per minute. Movements of the population around the area of the dispersed contaminant may need to be considered as the duration of the release increases. That is, the assumption that a person will be static for the time that contamination passes over him or her from the various sources is potentially untenable and this is explored below in section 4.
Breathing rate. The breathing rate is an input parameter for estimating inhalation exposure of workers. The default values in Table 12 are based on data from the US EPA Exposure Factors Handbook which covers breathing rates for men and women during different activity intensities going from ‘Sleep or nap’ to ‘High intensity’ (U.S. EPA, 2011). The breathing rates for the ‘light intensity’ and ‘moderate intensity’ activities have been incorporated into the software. A light intensity activity is defined as an activity with a MET value between 1.5 and 3, whereas a moderate intensity activity has a MET value between 3 and 6. MET stands for Metabolic Equivalent of Task and is a measure for the intensity of the activity. The 2011 Compendium of Physical Activities provides a list of MET values for more than 800 activities, including several farming activities. The MET values for these activities range between 1.8 and 7.8 with a value of 4.8 for harvesting activities (Xxxxxxxxx et al., 2011; Xxxxxxxxx et al., 2014). Both distributions and constant values (based on the mean values of the distributions) are available. Furthermore, the user can enter another value by selecting the “Constant – own value” option from the drop-down menu. Table 12 Distribution parameters for breathing rates of males and females (m³/hour). Source: U.S. EPA, 2011. Gender Intensity activity Breathing rate statistics in m³/hour Mean 5th 10th 25th 50th 75th 90th 95th Max Male1 Light 0,88 0,67 0,70 0,78 0,86 0,95 1,08 1,16 1,53 Moderate 1,96 1,34 1,44 1,68 1,88 2,22 2,50 2,75 4,23 Female1 Light 0,72 0,59 0,61 0,65 0,71 0,78 0,85 0,89 1,07 Moderate 1,51 1,13 1,19 1,31 1,46 1,69 1,91 2,10 2,92 1 The age group (51-61 years) for which the highest values were recorded in the EPA exposure factors handbook was selected.
