Posted By Paulo Dinis Hi folks ! I´ve done a search in IOSH forum´s using the term "colorimetric tubes" and since i´ve got zero result´s i´m posting this message. Here in Portugal, current Government have defined several criterias for company´s that pratices tecnical support/consultancy in the field of H&S at work. One of those criterias published in Portuguese national legislation, demands that the consultant company has to own risk assesment instruments. That is mandatory, and i´m only refering this as introduction. So, one of those "mandatory regulations criteria" in the field of chemical pollutants risk assesment exposure determine that the consultant company HAVE to own technical equipement in order to conduct such risk assesment. Ok, now the problem is that the "technical method refered by work inspection in Portugal" for determining personal exposure is based in colorimetric tubes.... I´ve used then in the past for "confined spaces work permit" and for a few "short term exposure situation", ie, TLV-C and TLV-STEL or even IDLH. The air volume sampling is around 50/100ml depending on the piston hand pump provided by the tubes manufacturer. Last year i´ve been able to convince my current employer to acquire an SKC sampling kit, but now this decision seems to be "unsuitable". In UK this method based on colorimetric tubes or difusion tubes is accepted as a valid method to determine the ACGIH/OSHA TLV-TWA ? Thank´s for input. Paulo Dinis H&S Manager Portugal

Posted By Paulo Dinis Hi gary, thank´s for input. Current context is not for an internal control but for risk assesment exposure, therefore we can consider it´s for legal purposes. Here in Portugal we don´t have National Standards that cover sampling and/or post analytical method ( in order to quantify with great confidence). In UK you seem to have several "standard method´s" as listed here http://www.hse.gov.uk/pubns/mdhs/index.htm In previous reading/studing about this subject i´ve concluded that detector tubes are used for screening to determine if whether additional sampling is needed. In the past i´ve done total dust, respirable dust and sampling for several chemical´s using sorbents tubes etc based on OSHA or ACGIH method´s. I conduct the sampling then send it to laboratory following shipment procedures described in method. "Draeger tubes" are sensible to pressure, humidity, temperature interferences of others substances presented in the workplace atmosfere etc. However in some situation they are certified, take a look here : http://www.osha.gov/dts/...micalsampling/field.html http://www.seinet.org/CPL/contents.htm Problem is that human beeing inhale around 70m3 of air on a 8 hours shift ("regular" work metabolism demands), and direct reading tubes only collect small volume of air then give an result for short term exposure that is "converted" to TWA. Due to the sampling tecnique plus laboratory cost, i can´t compete with other companies using this kind of "direct reading tubes". Employers ( with no tecnical knowledge to compare ) will definitely choose the less afordable proposal. So as you can imagine, it´s technical risk assesment accuracy method versus.... cost. Tubes are very very cheap when compared to sampling and analytical determination. My main concern is that this kind of risk assesment tecniques is accepted by work inspector here, but In Spain and Brazil they sure aren´t. I got the air sampling pumps ( count a balance too ) and the know-how to use them, but i´m sure i will not use it as much as i expected. Besides my employers getting real mad at me, i´m sure worker´s rights to a safe workplace is far from beeing served...

Posted By 9-Ship I was told colourmetric/stain tubes are really only for indication purposes only, as you have pointed out they are not very accurate and can be influenced by other environmntal factors. The error margin is something like 30%, hence they should not be used for measuring personal exposure.

Posted By Paulo Dinis Huge mistake ! Kevin Drew thanks for correction. Inhalation rate is 20m3/day for an adult of 70 kg. I had that number on my head from some toxico-kinetics study that I reviewed in the past. Check is here : http://www.atsdr.cdc.gov...PHA/marchafb/mar_p4.html look for Appendix D Calculations of risk for exposure situations assumptions and formulas. Thanks again for not letting this passed by. Paulo Dinis H&S Manager Portugal

Posted By Mike I have a few comments about "official" approval of gas detector tubes for determining compliance with limit values. There is a European Standard for short-term tubes EN1231:1996 which superseded an older BS5343. EN1231 applies to "a detector tube that provides a means of obtaining a rapid measurement (typically up to 15 mins) of the concentration of a specified chemical agent in air". Do any commercial tubes comply with EN1231? Well, yes and no. The manufacturers have never been put under pressure to claim compliance and the standard is little heard of, nevertheless from personal experience I am confident that in the essentials they do comply, namely clause 4.1.1 "At the lower limit of the specified measuring range, the relative overall uncertainty shall be <50 %; above 20 % of the specified measuring range the relative overall uncertainty shall be <30 %. With a few exceptions like asbestos and lead, regulatory authorities in EU member states should not mandate specific methods but be guided by the minimum performance requirements of EN482, EN1076, EN13890 and EN838. At least for 15 min STEL measurements gas detector tubes are acceptable and EN1231 was intended to allow them, but subject as always to expert interpretation/observation by an occupational hygienist. Long-term measurements are a different matter. They are not definitely excluded from EN1231 since you could have a sequence of 15 min estimates. There is a limited range of long-term stain-length diffusion tubes but no EN standard so far and with only one European manufacturer it is not certain when this will happen.