P. Roper, “The NIOSH Detector Tube Certification Program”, American. Industrial
... Shell-Lubricants, Corena P oil 100, Material Safety Data Sheet”, (dated.
Report
THE CONSIDERATIONS TO BE TAKEN INTO ACCOUNT WHEN SELECTING A LABORATORY AND SYSTEMS OF ANALYSIS OF COMPRESSED AIR FOR USE IN BREATHING APPARATUS TO MEET THE BS EN 12021:1999 STANDARD AND THOSE OF COSHH
by D. Thorburn Burns, B.Sc., M.A., Ph.D., D.Sc., F.I.C.I., C.Chem., F.R.S.C., M.R.I.A., F.R.S.E.
10/VIII/07
1
The discussion herein, deals with the problem of selection of analytical methodology and a laboratory for the analysis of air to comply with BS EN12021:1999 and COSHH in generic senses and not in relation to any specific analytical laboratories. To focus attention on the key points to be taken into account in making a technically valid choice of a method and of a laboratory the discussion is divided into 7 parts followed by the conclusions and the references to all sources cited , as follows : 1. The specification of the required air quality to meet the requirements of BS EN 12021:1999. 2. The criteria for the appropriateness of analytical method or methods to meet the requirements of BS EN 12021:1999 and also those of COSHH. 3. A critical assessment of “length of stain gas/vapour tubes” for the analysis of air to meet the requirements of BS EN 12021:1999 and also of COSHH regulations. 4. A. critical assessment of Fourier Transform Infrared spectrophotometry (FTIR) systems for the analysis of air to meet the requirements of BS EN 12021:1999 and also of COSHH regulations. 5. Assessment of instrumental methods alternative to FTIR for the analysis of air to meet the requirements of BS EN 12021:1999 and also of COSHH. 6. The determination of oxygen in air to meet the requirements of BS EN 12021:1999 and COSHH. 7. Elements of laboratory good practices to meet the requirements of BS EN 12021:1999 and COSHH. 8. Conclusions. 9. References.
2 1. THE SPECIFICATION OF REQUIRED AIR QUALITY TO MEET THE REQUIREMENTS OF BS EN 12021:199 To comply with the current standard, BS EN 12021:1999 the methods of analysis must be able to deliver reliable data for the constituents specified in the standard [1]. These are given in Section 6, Requirements, 6.1 Oxygen The oxygen content shall be in the range of (21±1) % by volume (dry air). 6.2 Contaminants 6.2.1 General Compressed air for breathing apparatus shall not contain any contaminants at a concentration which can cause harmful or toxic effects. In any event all contaminants shall be kept as low as possible and shall be far below the national exposure limit. Combination effects of more than one contaminant shall be taken into account. In the absence of more stringent national requirements the values of 6.2.2 to 6.2.5 shall be applied. NOTE. The limit of concentration for any contaminant should be derived from national exposure levels taking into account as far as practical the effects of pressure and exposure time. 6.2.2 Lubricants Lubricant content (droplets or mist) shall not exceed 0.5 mg/m3. Where synthetic lubricants are present 6.2.1 applies. 6.2.3 Odour and taste The air shall be without significant taste or odour 6.2.4 Carbon dioxide content The carbon dioxide content shall not exceed 500 ml/m3 (500 ppm). 6.2.5 Carbon monoxide content The carbon monoxide content shall be as low as possible but not exceed 15 ml/m3 (15 ppm). 6.3 Water content 6.3.1 There shall be no free liquid water. 6.3.2 Air for compressed air line breathing apparatus shall have a dewpoint sufficiently low to prevent condensation and freezing. Where the apparatus is used and stored at a known temperature the pressure dewpoint shall be at least 5oC below the likely lowest temperature. Where conditions of usage and storage of the compressed air supply is not known the pressure dewpoint shall not exceed -11oC.
3 6.3.3 The maximum water content of air at atmospheric pressure given in Table 1 shall be used. Table 1 Nominal pressure Maximum water content of Air at atmospheric pressure bar mg/m3 40 to 200 50 > 200 35 NOTE The water content of the air supplied by the compressor for filling 200 bar or 300 bar cylinders should not exceed 25 mg/m3 .
It should be noted that all the Requirements, apart from the oxygen content, are expressed in terms of upper allowable limits. The analyst does not have to certify the amounts of the analytes found (other than that for oxygen) but that the amount found present for an analyte is below the specified limit. Section 7 of BS EN 12021:1999, Sampling and testing, states “Any appropriate method may be employed, provided it conforms with the following general requirements: - for measuring and assessing results the accuracy of the method shall be taken in consideration, and - the detection limit of the method employed shall be below the required limit value.” NOTE The National foreword to BS EN 12021:1999 states “This British Standard is the English Language version of EN 12021:1998.” It goes on to state how clause 6.2.1 is to be interpreted and applied. Clause 6.2.1 of this European Standard requires that, “in any event all contaminants shall be kept as low as possible and shall be below the national exposure limit”. National Occupational Exposure Limits (OEL) for substances hazardous to health are published yearly by the Health and Safety Executive and can be found in Guidance Note, Occupational exposure limits (EH40). In the context of this European Standard “below the national limit” will mean that the concentration should be not greater than 10% of the relevant time (8 h) weighted average OEL. 2. THE CRITERIA FOR THE APPROPRIATNESS OF A METHOD OR METHODS TO MEET THE REQUIREMENTS OF BS EN 12021:1999 AND ALSO THOSE OF COSHH REGULATIONS The criteria for appropriate method or methods to deal with BS EN 12021:1999 are dictated by the absolute necessity to be able to provide reliable data so that the analyst can certify that all the quality requirements have been meet.
4 It should be noted that in requirement 6.2.1 General it states “Compressed air for breathing apparatus shall not contain any contaminants at a concentration which can cause toxic or harmful effects”. Thus the analyst must have the facility to look for contaminants additional to those specified. The provision of a valid assurances of the absence of significant amounts of contaminants additional to oil, carbon monoxide and carbon dioxide in breathing air is necessary for any employer to act with the proper duty of care towards employees, the consumers of the breathing air supplied. The duty of care to protect the health of their workforce is also a general and mandatory requirement under the Health and Safety at Work Act. Now, with the Control of Substances Hazardous to Health (COSHH) Regulations the duties of employers are now stated more clearly and in more detail in particular with regard to Analytical quality in workplace air monitoring [2]. Thus in addition to appropriate methods for the individual specified analytes, namely oxygen, lubricant, carbon dioxide, carbon monoxide and water it is necessary for a laboratory to undertake air analysis to the requirements of BS EN 12021:1999 to have a system in place to detect and identify the presence of the great range of compounds that may be present in compressed air. These compounds arise from the compressor oil and its additives, the decomposition products of the oil and its additives, residual materials used in cleaning and servicing the compressor and system, materials in the intake air etc. The sources and the contaminant compounds can vary from sample to sample, in unpredictable manners.
3. A CRITICAL ASSESMENT OF THE USE OF “LENGTH OF STAIN GAS/VAPOUR DETECTOR TUBES” FOR THE ANALYSIS OF AIR TO MEET THE REQUIREMENTS OF BS EN 12021:1999 AND ALSO OF COSHH REGULATIONS “Length of stain gas/vapour detector tubes” are commonly used to monitor work place environments for specific compounds for Health and Safety at Work purposes. This is a valid approach provided a detector tube exists for the compound of interest with the required detection limit and it is used when no cross reacting compounds are present. For the particular application, the analysis of breathing air, the analyst needs to be satisfied that detector tubes are available for each analyte sought, with adequate detection limits and will produce data with adequate accuracy. Detector tubes are available from, for example, Dräger [3] with measuring ranges and low cross sensitivities to meet BS EN 12021:1999 for carbon dioxide, carbon monoxide and water but not for oil, as will be discussed later in detail.
5 It should be noted that BS ISO 8573-5:2001 “Compressed Air- Part 5; Test methods for oil vapour and organic solvent content” [4], in clause 5 Test Methods, states for oil vapour content “Chemical indicator tubes are to be used as a preliminary method only”. It is considered significant that ASTM D4490-96 “Standard Practice for Measuring the Concentration of Toxic Gases or Vapors Using Detector Tube” [5] is now listed as Superseded, and attention is drawn to, “This standard does not purport to address all the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use”. Due to the limited number of compounds for which tubes are available it is not possible to deal with the duty of care to deal with “any contaminant” as required in BS EN 12021:1999 in section 6.2.1 General. The accuracy of measurement is also an important factor in assessing as to whether or not an analytical procedure is appropriate for purpose. There is a reasonable consensus in the publications from the relevant standards institutions concerned with analytical measurements with regard to the accuracy of a length of stain measurement. The accuracy of a single measurement is the difference between the true value and the measured value. For repeated measurements one would obtain a mean and a standard deviation (σ). If a single measurement is accepted as an estimate of the concentration of a component in the sample, the best we can say of a single measurement result is that the true result lies within the range, the measured result ± 2 σ. In order to apply this concept it is necessary to know the value of the standard deviation for the compound being determined with the measurement system in use and at the level of concentration being determined. The ASTM state [5, 6] “the accuracy of dosimeter tubes is generally within the range of ± 25%”. For certification of detector tube units in accordance with ANSI/ISEA 1021990(R2003) [7, 8], based on earlier work by NIOSH [9], it is stated “The accuracy of readings must be ± 35% at 0.5 times the TLV (Threshold Limit Value) and 25% at 1.0 to 5.0 times of the gas or vapour”. The use of length of stain detector tubes for oil and oil mist raises particular problems for the analyst because “oil” is not a unique chemical compound or blend of compounds. There are two main groups of compressor oils, containing a mineral oil or synthetic (diester) oil as base material. Both oil types contain additives which vary from oil to oil and from manufacturer to manufacturer. Most of the additives are intrinsically toxic as are noted in the manufacturers safety data sheets [see for example 10, 11], or have toxic breakdown products. The determination by the Draeger tube method for a single mineral oil mist has been compared with that obtained using Infrared spectrophotometry by the UKAEA for the Offshore Safety Division of the Health and Safety Executive. For the Infrared method the
6 oil mist was trapped in a cellulose filter, washed of with trichlorotrifluoroethane, made up to 10ml and the spectra recorded 3100-2700cm-1. Standards were prepared in the same solvent with the original oil and a calibration graph obtained from the-CH2- absorption at 2930cm-1. This procedure is based on the NISH Method 5026, for mineral oil mist [12], which states “the method is applicable to all trichlorofluoroethane-soluble mineral oil mists, but not to (nor does OSHA’s standard cover) semi-synthetic or synthetic oils”. The results are given in Report-OTO97810 [13] which states “comparison of results on oil mist concentration by the two methods indicated that the Draeger tubes gave significantly lower readings compared to the IR method”. The author comments, “Indicator tubes….suffer to some extent from the rather subjective interpretation of the colour intensity formed at the lower end of the concentration range”. The report also notes that “Information was sought from the UK Drägerwerk agents concerning the method of calibration of their tubes but no useful information was forthcoming”. Studies reported by Factair [14] using an extremely wide range of 317 oils gave detection limits with Draeger oil tubes, from “not measurable” for 27 of the oils, and a variable, wide range of response, 4.5 to 45 µg, for the rest. It should be noted that ISEA do not certify any manufacturer for a “length of stain tube” for oil mist in air [15]. The inevitable conclusions from the information (all of which is in the public domain), summarised above, are that 1. Dräger or similar “length of stain tubes” cannot provide the analytical data necessary to satisfy the requirements of BS EN 12021:1999, specifically with regard to Lubricants. 2. Dräger or similar “length of stain tubes” cannot provide the analytical data necessary to satisfy BS EN 12021:1999, specifically with regard to 6.2.1 General which refers to “any contaminant”. 3. Dräger or similar “length of stain tubes” cannot provide the analytical data necessary to meet the requirements of COSHH regulations, where the identities of compounds as well as their amounts have to be established in relation to occupational exposure limits. 4. A CRITICAL ASSESMENT OF FOURIER TRANSFORM INFRARED SPECTROPHOTOMETRY GAS ANALYSIS SYSTEMS FOR THE ANALYSIS OF AIR TO MEET THE REQUIREMENTS OF BS EN 12021:1999 AND OF COSHH REGULATIONS Fourier Transform Infrared Spectrophotometry (FTIR) is commonly the method of choice in North America for applications in which the detection of a wide range of contaminants in air is required. It is adopted as the normative method for the determination of trace contaminants in MOD Defence Standard 68-284 for “Compressed Breathing Gases for Aircraft, Diving and Marine Life-Support Applications” [16], MOD Defense Standard 02-373 Code of Practice for Compressed Air Systems Cleanliness”
7 [17] and MOD Defence Standard 58-96 “Pure Gases for Weapon Systems and Detector Cooling Applications” [18]. Infra-red absorption is also listed in the HSE Research Report 424, “Performance of diving equipment” [19] for use, “Where testing for additional components was required (e.g. suspected organic constituents) air samples were analysed by gas chromatography, mass spectrometry or infra-red absorption”. In the light of breathing gas analysis and other critical applications of infrared spectrophotometry it is not surprising to find that several internationally accepted codes of good laboratory practice exist for this technique [20-22]. In addition to the detection, identification and estimation of trace organic contaminants in air FTIR may also be used to determine carbon dioxide, carbon monoxide and water vapour, three explicitly listed compounds subject to concentration limits in BS EN 12021:1999. The overall quality of test data obtained using FTIR is greatly superior to even the best that can be obtained by those “length of stain tubes” which have a low cross reactivity. ASTM state that for FTIR, “In practice, an accuracy of 10% and a precision of 5% are routinely observed” [20]. The well documented problems with mineral oils and synthetic oils, their detection and estimation, have been discussed in Section 3, above. Both oil types can be detected and identified by FTIR from unique spectral details at amounts well below 0.5mg/m3. For mineral oils (hydrocarbon mixtures) their content in air can be easily referenced, via the C-H stretching frequencies to methane in air standards, and hence to long chain hydrocarbon, oil. From practical operational as well as from legislative compliance view points, analysis by FTIR has many advantages over “length of stain tubes”. Among the most relevant to the analysis of breathing air to meet the requirements of BS EN 12021:1999 can be listed, 1. It provides data that can meet the requirements of BS EN 12021:1998 and COSHH, apart from that of the determination of oxygen. 2. All the data can be obtained in a single run. 3. The examination of an IR spectrum is made by well established procedures; the conclusions can be readily confirmed by an expert external to the laboratory originating the spectrum. 4. The system can be calibrated against readily available standards for the unique compounds, carbon monoxide, carbon dioxide and water vapour, whose upper acceptable limits are stated in BS EN 12021:1999. 5. The presence of any residual oil of both mineral and synthetic types are readily detected and identified, an analysis which cannot be done using “length of stain tubes”. 6. Although the capital outlay for equipment is high, the running costs are not excessive and sample through-put can be high. 7. The recorded spectrum can be stored indefinitely. IR spectra are excellent evidence to support compliance with due diligence, and with duty of care, should these be questioned.
8 5. VIABLE ALTERNATIVES TO FTIR FOR THE ANALYSIS OF AIR TO MEET THE REQUIREMENTS OF BS EN 12021:1999 AND COSHH The particular importance of FTIR to the present discussion lies in its multi-analyte capabilities. As noted in the recent HSE Research Report 424 [19], in addition to FTIR organic contaminants in air may be tested for by using gas chromatography or by using mass spectrophotometry. Mass spectrophotometry [23] has the advantage over gas chromatography in that, like FTIR, it produces data that permits the deduction of the structural identity of the components detected, an essential feature to be able to deal with the requirement in both BS EN 12021:1999 and COSHH to achieve multi-analyte examination deal with “any contaminant”. The main disadvantage of mass spectrometry as compared to FTIR is in its’ higher capital, higher maintenance and higher running costs. WWW searches show, for example, in North America, FTIR is the method of first choice for laboratories supplying customers with detailed analyses of breathing air.
6. THE DETERMINATION OF OXYGEN IN AIR TO MEET THE RQUIREMENTS OF BS EN 12021:1999 BS EN 12021:1999 requires that the oxygen content of air shall be in the range (21 ± 1) % by volume. A number of methods exist ranging from classical volumetric procedures based on the chemical absorption of oxygen to instrumental methods gas chromatographic separation of oxygen from the other components of air or based on oxygen’s specific magnetic or electrochemical properties [24]. Numerous commercial instruments are available based on all three instrumental methods listed. Fifteen commercially available instruments based on electrochemical sensors were assessed for NIOSH by Woodfin and Woebkenberg who found, under laboratory conditions, a standard deviation of ±0.52 % for 15 different instruments for over 100 readings over an 8-h period [25], thus adequate to meet BS EN 12021:1999. 7. ELEMENTS OF LABORATORY PRACTICES TO MEET THE REQUIREMENTS OF BS EN 12021:1999 AND COSHH Both national and international guides to good practices for laboratories engaged in air monitoring are available. Both that from the HSE in MDHS 71 [2] and that from ASTM in D 3614-97(reapproved 2002) [26] stress the importance of internal quality control and the role of the Quality Manager. The ASTM guide is the more detailed and presents the key features of organizations, facilities and operations which by their selection and control affect the reliability and
9 credibility of the data generated. Most importantly the minimum personnel and their qualifications are made absolutely clear and explicit starting with:“The Director – The laboratory director should be a full-time employee of the organization that operates the laboratory. He or she should have an earned baccalaureate degree in science or engineering from an accredited college or university or the equivalent with a minimum of 5 years experience in sampling and analysis of atmospheres or in a related field. The director should have the following responsibilities: 1. Selection and approval of the methods of sampling and analysis, 2. Implementation of a quality assurance program to describe the quality of technical data, 3. Development of standards of performance and evaluation of personnel by these standards, and 4. Training of personnel.” The qualifications and the necessary experience of the Laboratory Supervisor, the Senior Staff, the Technical Staff and Support Staff are also outlined in ASTM D 3614-97. Although the academic qualifications and experience of the laboratory personnel are not stated in MDHS 71, they would need to be similar to those in ASTM D 3614-97 in order for data produced by the laboratory to pass examination for compliance with Health and Safety at Work Regulations. CONCLUSIONS In order to meet the requirements of BS EN 12021:1999 and COSHH it is necessary to carry out multi-analyte examination of air samples, for example using FTIR, to provide the necessary information with regard to the content of carbon dioxide, carbon monoxide, water, lubricant and any other contaminants. In addition, it is necessary to obtain a reliable determination for the oxygen content of an air sample. Such analyses must be conducted by an appropriately equipped laboratory which has an adequate quality assurance programme in place and which employs suitably qualified and experienced staff to both obtain and to interpret the data. “Length of stain tube” methods do not satisfy the requirements in BS EN 12021:1999 for Lubricants, nor are they capable of the necessary multi-analyte examinations which are required to search for and rule out the presence the wide range of possible contaminants that can be found in compressed air samples. STATEMENT I am aware that my duties are to the court and that the opinions and the conclusions I have reached were not influenced by those instructing me.
10 9. REFERENCES 1. British Standards Institution, BS EN 12021:1999, “Respiratory protection devices-Compressed air for breathing apparatus”, BSI, London, (1999). 2. Health and Safety Executive, MDHS 71, “Methods for the Determination of Hazardous Substances. Analytical quality in workplace air monitoring”, HSE, London, (March 1991). 3. See “Short term measurements with Draeger tubes” at www.draeger.com. 4. British Standards Institution, BS ISO 8573-5:2001, “Compressed air-Part 5: Test methods for oil vapour and organic solvent content”, BSI, London, (2002) 5. ASTM, Historical Standard, Designation 4490-96, “Standard Practice for Measuring the Concentration of Toxic Gases or Vapors Using Detector Tubes”, ASTM International, West Conshohocken, (2007). Copies of the 1996 and 2006 supplied for information. 6. ASTM, Active Standard, Designation: D 4599-03, “Standard Practice for Measuring the Concentration of Toxic Gases or Vapors Using Length-of-Stain Dosimeters”, ASTM International, West Conshohocken, (2007). Copies of the 1997 and 2006 (as current) versions are supplied for information. 7. Editorial, “Gas Detector Tube Unit Certification Update”, SEI UPDATE, Vol. 18(1), 5, (March 2004). 8. International Safety Equipment Association, ANSI/ISEA 102-1990 (R2003), “American National Standard for Gas Detector Tube Units-Short Term Type for Toxic Gases and Vapors in Working Environments”, ISEA, Arlington, (2003). 9. P. Roper, “The NIOSH Detector Tube Certification Program”, American Industrial Hygiene Association Journal, Vol. 35, 438-442, (1974). 10. Anderol, “Anderol 555, Safety Data Sheet”, (dated 08/31/2005), notes this diester based synthetic compressor lubricant contains N-Phenyl-1-naphthylamine and also Diphenylamine. 11. Shell-Lubricants, Corena P oil 100, Material Safety Data Sheet”, (dated 9/11/2003), notes this petroleum distillate based oil contains proprietary additives (contains
