Mine Health and Safety Act, 1996 (Act No. 29 of 1996)RegulationsGuideline for a Mandatory Code of PracticeOccupational Health Programme (Occupational Hygiene and Medical Surveillance) on Personal Exposure to Airborne PollutantsAnnexuresAnnexure E : Background information, sampling and analysis on particulates7. Filters |
The selection of a particular filter type for a specific application is invariably the result of a compromise of many factors. These factors include cost, availability, collection efficiency, analytical requirements and the ability of the filters to retain its filtering properties and physical integrity under the ambient sampling conditions. The sampling methodology adopted will determine the type of filter required. Recognized methodologies such as HSE or NIOSH analytical methods must be consulted. A suitable backing pad is required to support the filter disk in the cassette.
| 7.1 | Correction for the influence of moisture |
Due to the hygroscopic nature of most filters, it is necessary to quantify any variation in their moisture content. Reference filters are thus used in the weighing procedure as follows:
| • | Reference filters always remain in the weighing room and are weighed during both the "before" and "after mass determinations of field filters. |
| • | Any variation in mass between the "before" and "after" mass measurements will reflect the change in moisture content, This variance is then accordingly used to correct the mass of the field filter. |
| 7.2 | Weighing errors |
A maximum allowable variation of 0.05mg in the mass of filters in three consecutive weighings of the same filter, is allowed. Should these three measurements vary by more than the value mentioned above repeated mass determination must be performed.
| 7.3 | Preparation of filters |
An important step in ensuring accurate results and records is the correct marking and preparation of filters.
| 7.4 | Identification of filters |
| (i) | Filters from individual packs must be readily identified by means of a suitable marking system. A ball point pen can be used to mark filters. Marking to be done on the backing-pad facing down to be readable from the bottom as the chemicals in ink sometimes interfere with chemical analyses. |
| (ii) | In order to ascertain the hygroscopic character variances between individual filters with acceptable accuracy, three reference filters must be selected from each batch/pack which must not contain more than 100 filters. |
| (iii) | These field and reference filters must be stored in petri-slides until needed. |
| 7.5 | Treatment of filters prior to weighing |
Filters
| (i) | At least 12-hours before filters are due to be weighed the required number must be placed in a partially open Petri slide/dish in the stabilisation cabinet/chamber. |
| (ii) | At the same time the Petri slide/dish containing the relevant reference filters must be partially opened and placed in the same cabinet/chamber for the same period of time. |