Posted By Mac Hi Can you assess against these limits without air monitoring and if so how and where do you get the reference data from? EG: If someone is to drill into AIB to fix fire dectors, but job will take an hour within 7 days is it necessary to carry out personal air tests to establish if thie limits will be exceeded? Surely if the work is of short duration and the sporadic and low intensity peak exposure limit is exceeded, the job will be done by the time the analysis in complete - too late to react. Also, how would you measure against the 4hr control limit if the job takes 1hr, do you simply divide the f/ml counted over 1hr by 4? Can someone please help to make this a little bit more clear to me, maybe with some worked examples. MAC

Posted By Mac Dave Thanks for your response, I have been reading up on L143, HSG247 & HSG248 and I am starting to see the light but am still pretty hazy with a few points. Please tell me if I am on the right track with the following: Sporadic & low intensity exposure is defined by a limit of 0.6 f/cm3 measured continuously over 10mins (f/cm3 is the same as f/ml? how does that work for a start?!) So, when carrying out a RA for work which my disturb or damage asbestos of any kind (as required by CAR 2006) you must establish if this level will be exceeded and can use the following the following data - Table 1.1 & 1.2 in the contractors guide, HSE asbestos essentials or historical air sampling evidence from previous works, to estimate likely fibre concentrations. But if you’re in a situation which none of these sources of info cover, you must carry out personal air monitoring. First question (s) – to sample for this 10min level should the flow rates, volume etc used be the same as in table 5.2 (pg 15) of the analysts guide i.e: 4 litres/min giving 40 litres sampled then 100 graticules counted, with a limit of quantification of 0.24 f/ml. If so what bearing has the 0.24 figure on the fibre concentration as it is below the 0.6 limit? Is it only there because you cannot reliably calculate concentrations below 0.24 or is it used in the interpretation of the sample as with clearance, background & reassurance samples where the limit of quantification for the same fibre concentration is 0.01 f/ml? EG: Lets assume that a fitter has to strip a valve for maintenance work (for the sake of this example there is no other data available), he/she has had asbestos training and has been given RPE & PPE, this work will take 20min and a personal air sample is taken at 4 litres for 10min and 80 fibre ends are counted, this will give a fibre concentration of 4.8 f/ml, (this figure is above the limit of quantification of 0.24, should you take any action?) the result is below the sporadic and low intensity limit of 0.6 f/ml therefore no licence required. But what if the fibre concentration was 0.8 f/ml? By the time the analyst had a result the work & exposure would be over. On top of this you must be sure that the exposure does not exceed the control limit of 0.1 f/ml which I am guessing is a Time Weighted Average over 4hrs (also from the analysts guide), how does this work?? My understanding is this. TWA considers work activities over a 4hr period. So let’s say wee Jimmy the fitter does various jobs in 4hrs while wearing a personal with the following fibre concentration results: - 2hrs at 0.01 f/ml, 1 hr at 0.02 f/ml, 0.5hr at 0.08 f/ml and a half hr break 2 x 0.01 = 0.02, 1x 0.02 = 0.02, 0.5 x 0.08 = 0.04, 0.5 x 0 = 0 add them up and divide by 4 = 0. 08, which is under the control limit but above clearance indicator level so controls, procedures, RPE/PPE still required. Is this correct the correct way to work it??? Also if planned work is short duration (i.e less than 1hr per person not in excess of 2hrs in total) you can measure for the sporadic & low intensity limit but how do you check if you are within the 4hr control limit?? I have to stop thinking about this for a while now as I am slowly losing the will to live. Dave (or any other practitioners) your comments and input on what I have said will be most appreciated. MAC

Posted By Mac Mal I think the sporadic and low intensity STEL is higher because the exposure time (10mins) is much shorter than the control limit (4hrs). The idea being that the more asbestos fibres you breathe and the longer you breathe them for, the higher chance you have of getting asbestosis etc. So what they seem to be saying is you can expose employees to 0.6 f/ml for up to 10mins (which works out as 600,000 asbestos fibres in a metre cubed, multiplied by the volume of the room in question). But an employee can only be exposed to a maximum 0.1 f/ml averaged over 4hrs (works out at 100,000 asbestos fibres per metre cubed). Not the sort of levels I would like to be breathing. Also if you breach the 0.6 level you will breach the 0.1 level straight away as 0.6/4 (hrs)= 0.15. Clear as mud I think! Anybody out there work for UKAS or HSE or run a UKAS lab who can answer my questions?? Any help would be appreciated. MAC If preferable email me direct at macartneychris@yahoo.com

Posted By Adrian Watson Dear All, In occupational hygiene it is normal to have excursion factors for use with the Long Term Exposure Limit; this is normally the Short Term Exposure Limit. Where there is no Short Term Exposure Limit the TLV's use 3 x the 8-H TWA for a total of up to 30 minutes a day, with an overriding limit of 5 x the 8H-TWA providing the 8H-TWA is not exceeded. The German MAC system however, uses a variable limit dependant upon the health effect of the substance. The Control of Asbestos Regulations set a control limit of 0.1 fbr/ml averaged over 4 hours; therefore if you had a peak exposure of 24.0 fibres over 1 minute, with no exposure for the remainder of the period, this equates to an average exposure of 0.1 fbr/ml. To prevent exposure to this level HSC/HSE advise an overriding concentration of 0.6 fbr/ml averaged over 10 minutes. This is not a limit, it is not in the regulations and it is not in the ACOP; it is guidance offered by the HSC/HSE (in the acop document, para 32 refers) as to what they consider the upper limit of low intensity exposure to be. This means you can be exposed to a concentration of maximum concentration of 0.6 fbr/ml averaged over 10 minutes providing you do not exceed the average concentration of 0.1 fbr/ml. e.g. You can be exposed to a maximum concentration of 6.0 fbr/ml and 0 for 9 fbr/ml for the remainder of the period and you will not have exceeded the 0.6 fbr/ml average over 10 minutes; you can do this 4 times in 4 hours and you will not have exceeded the 0.1 fbr/ml averaged over 4 hours. Regards Adrian Watson

Posted By Adrian Watson Dear All, In occupational hygiene it is normal to have excursion factors for use with the Long Term Exposure Limit; this is normally the Short Term Exposure Limit. Where there is no Short Term Exposure Limit the TLV's use 3 x the 8-H TWA for a total of up to 30 minutes a day, with an overriding limit of 5 x the 8H-TWA providing the 8H-TWA is not exceeded. The German MAC system however, uses a variable limit dependant upon the health effect of the substance. The Control of Asbestos Regulations set a control limit of 0.1 fbr/ml averaged over 4 hours; therefore if you had a peak exposure of 24.0 fibres over 1 minute, with no exposure for the remainder of the period, this equates to an average exposure of 0.1 fbr/ml. To prevent exposure to this level HSC/HSE advise an overriding concentration of 0.6 fbr/ml averaged over 10 minutes. This is not a limit, it is not in the regulations and it is not in the ACOP; it is guidance offered by the HSC/HSE (in the acop document, para 32 refers) as to what they consider the upper limit of low intensity exposure to be. This means you can be exposed to a concentration of maximum concentration of 0.6 fbr/ml averaged over 10 minutes providing you do not exceed 0.1 fbr/ml average concentration over 4 hours. e.g. You can be exposed to a maximum concentration of 6.0 fbr/ml and 0 fbr/ml for the remainder of the 10 minute period and you will not have exceeded the 0.6 fbr/ml average over 10 minutes; you can do this 4 times in 4 hours and you will not have exceeded the 0.1 fbr/ml averaged over 4 hours. Regards Adrian Watson

Posted By Adrian Watson Mac, 1. Yes f/ml is the same as f/cubic cm. (f/cm^3) 2. The limit of quantification (0.24 f/ml) is the concentration below which fibres cannot be reliably counted with the flow rate and the counting method. It has no other meaning. 3. Your stripper has a concentration of 4.8 f/ml, so what is the task duration? If the average concentration is greater than 0.6 f/ml averaged over 10 minutes the task is notifiable. 0.8 f/ml over 7.5 mins > 0.6 f/ml over 10 minutes = notifiable. 4. 2hrs at 0.01 f/ml, 1 hr at 0.02 f/ml, 0.5hr at 0.08 f/ml and a half hr break at 0 f/ml so yes to controls and plan of works but no to RPE/PPE. 5. You have to calculate or measure to determine whether you are within the 4hr control limit. Regards Adrian

Posted By Dave Wilson Check hse www and look at the task sheets, if there is a job there you are planning to do then for the purposes of SALI then that work will fall under that category, I wouldn't get hung up on the STEL & MEL as if the job you are planning is greater than what is on the task sheets then it will not be SALI and a licensed contractor has to be used as the task sheets say so!