AS NZS 2243.9:2009 Safety in laboratories
6.6.1 General
Retention takes place progressively through the filter with the saturation zone moving from the inlet side to the exhaust side of the filter. The saturated zone is preceded by a partially- saturated zone and there is an initial breakthrough by the contaminant when this partially- saturated zone reaches the exhaust surface of the filter. Thereafter the percentage of contaminant that escapes filtration increases until total saturation of the filter is reached.
Filter monitoring should aim to detect a point between initial breakthrough and the point at which the concentration of contaminant escaping reaches the occupational exposure standard for that substance. The detection point shall be selected on the basis of the results of the risk assessment for the situation, taking into account available monitoring methods suitable for the exposure standard for that substance. Filter monitoring shall ensure the escape of contaminant is detected prior to it reaching the occupational exposure standard. Regular monitoring of the recirculating fume cabinet shall be performed as part of the routine laboratory procedures.
NOTE: A system using two filters in series with monitoring being conducted between the filters is recommended for fume of particular concern.
6.6.2.1 General
Since the recirculating fume cabinet relies on the continuing efficiency of its filtration and retention system for safe recirculation of its exhaust, the system shall be regularly tested and maintained, e.g. by filter cleaning or replacement at appropriate intervals.
Manufacturers should be consulted to provide information on the volume of fumes each particular model is likely to be able to retain before filters reach saturation point and the temperature and humidity conditions that can affect filter efficiency.
6.6.2.3 Saturation of the filter
The filter material has a limited capacity to absorb fume. This will vary with the particular chemical compound used and any previous or simultaneous exposure to other chemicals. Consequently, it is difficult to accurately predict the working life of the filter. Early detection of fume break through or filter saturation can be determined by checking for fumes on the exhaust side of the filter. While this may be a satisfactory procedure for chemicals with a strong odour and low toxicity, there is an unacceptable level of risk with highly toxic material of no detectable odour. For such materials, a system for identifying filter saturation such as that described in the Note to Clause 6.6.1 should be implemented. Regular weekly testing of the exhaust for the offending fume using test kits may be satisfactory for material of moderate toxicity.