Airborne dust levels generated during insulation with MMMF: a laboratory investigation

A laboratory study has been undertaken to investigate the potential risks associated with the use of man-made mineral fibre (MMMF) insulation wools. The study comprised an assessment of the MMMF properties which could affect airborne fibre levels and measurement of fibre emission hi a standardised dust box test followed by full scale insulation trials in a small room.In the preliminary work, sixteen samples were tested : eleven rockwool, two glasswool and three samples (2 rock and one glass) which had been heat treated to remove the oil from the surface of the fibres. Each sample was analysed to determine its oil content and density and then subjected to the dust box test. This test was carried out in a 0.18 m3 box by agitating the MMMF at 4 Hz in a shaker unit. The concentration of fibres inside the box was determined by collecting airborne dust samples onto membrane filters and counting the number of respirable fibres using a phase contrast optical microscope.These tests confirmed previous investigations which had shown that the presence of more than about 0.1% oil effectively suppressed the release of airborne fibres. Additionally, there was no indication that the density of the MMMF, over the range of 40 to 170 kg/m3, had any effect on the quantity of fibres released.The full scale insulation trials were carried out in two ways: insulation of a test rig, comprising pipes, cylindrical sections and flanges and on the flat surfaces within the room, i.e. the walls and ceiling. Throughout the tests the air exchange rate, within the room, was maintained constant at approximately 3 air changes per hour by means of a wall mounted fan. Four tests were carried out using the test rig (3 rockwool and one glasswool) and six on flat surfaces (3 rockwool, 2 glasswool and one with previously used rockwool, recovered from a coal fired power station). Airborne dust samples were collected from those carrying out the insulation work and from fixed locations within the room. The samples were either designed to measure total inhalable dust, by gravimetric assessment or airborne respirable fibres using phase contrast microscopic analysis.In the tests where MMMF slabs were applied to the flat surfaces the concentrations were low, with respirable fibre concentrations less than 0.3 fibres/ml and total inhalable mass concentrations less than 7.4 mg/m3. The corresponding airborne dust levels from the test rig were consistantly higher than the results from the flat surface application, typically respirable fibre concentrations ranged from 0.5 – 1.0 fibre/ml and mass concentrations generally exceeded 5 mg/m3.This was attributed to the additional handling and cutting required to insulate the rig. The highest mass concentrations were found when rockwool mattress was used, either on flat surfaces or the test rig. In these situations the concentration was approximately 20 mg/m3 for new materials and more than 100 mg/m3 for the old material recovered from the coal fired power station. The majority of dust, in the latter case, arose from coal and ash contaminating the MMMF.Overall, these data indicated that when using MMMF insulation wools it is more likely that the total inhalable dust concentration would exceed the 5g/m3 maximum exposure limit for MMMF than the fibre concentration exceed a fibre number based on occupational exposure limit.A small number of trials were carried out at a higher ventilation rate: approximately 8 air changes per hour.The airborne mass and fibre concentrations, in these tests, were approximately two thirds those found in the corresponding tests where there were lower ventilation rates.The report also compares personal and static concentrations obtained throughout all of these tests and concludes that it is very unlikely that workers, not directly handling MMMF insulation, would have personal gravimetric concentrations greater than the 5 mg/m3 maximum exposure limit.The report ends with a discussion of the results in relation to the COSHH Regulations. It is recommended that steps should be taken to control airborne dust levels when MMMF insulation is applied or removed. This would include, where possible, choosing materials with at least 0.1% oil and with relatively coarse fibres and providing at least 10 air changes per hour in the work environment. If this were done then only when rockwool mattress was being worked would additional controls be necessary. In these situations it is recommended that local exhaust ventilation, or where this was not reasonably practicable, suitable respiratory protection should be used. “”