Frequency of surface contacts. The hand model applies event frequencies to provide an indication of surface contact frequencies. The following event frequencies are included in the hand model (see Table 10): • Surface contacts with the vehicle cockpit is represented by events of stepping into/out of the vehicle, i.e. the number of mixing & loading periods (Fmlp) and number of times leaving the vehicle during trouble-shooting or nozzle maintenance (Fnr) • Surface contacts with the delivery system/rig is represented by (i) trouble-shooting and nozzle maintenance events (Fnr) and (ii) incidental contacts such as (de-)mounting and boom (un)folding prior to and after spraying (Frig) The mixing & loading periods (Fmlp) are estimated from the volume applied and the tank volume. The volume applied parameter is estimated from user inputs and are based on the total area sprayed (Ha), dose (kg/Ha) and final mixing & loading concentration (g/l). To determine the frequency of nozzle maintenance (Fnr), information on the frequency of trouble shooting/nozzle maintenance during boom spraying (x.x. Xxxxxxxx et al, 2009; Xxxx & Xxxxx, 1988) was consulted. For the BS dermal hand model, a default of 3 nozzle maintenance events during spraying operations is proposed. When testing the model with data (with no information of nozzle maintenance frequencies), it is assumed that contact events with the nozzles during spraying (Fnr) are between 0 and a worst case of 15, with a 90% probability of between 0 and 5 and 10% probability of between 6 and 15. Other events that may occur prior to or after spraying activities include nozzle replacement, (de-) mounting of the rig and manual boom (un)folding. A fixed event frequency with the rig and nozzles before and after spraying (Frig) is set at 1. Frig are not included as user input assuming that this is not a known input. These values may be updated with evidence of frequencies of different activities during boom spraying with different vehicle-sprayer types (e.g. Lebailly et al, 2009).
