WO1994001753A1

WO1994001753A1 - Sampling device for airborne particulate or vapour emissions

Info

Publication number: WO1994001753A1
Application number: PCT/AU1993/000346
Authority: WO
Inventors: Peter J. Kirton
Original assignee: The Broken Hill Proprietary Company Limited
Priority date: 1992-07-13
Filing date: 1993-07-13
Publication date: 1994-01-20
Also published as: GB9500705D0; NZ253980A; GB2283816A; GB2283816B

Abstract

A device (3) for sampling airborne particulate or vapour emissions, such as polycyclic aromatic hydrocarbon emissions, comprises: a main sampler body (21) and a sampling head (23) detachably coupled to the sampler body (21). The device (3) further comprises a passage (7) formed in the sampler body (21) with the sampling head (23) defining an inlet to the passage (7). The device (3) further comprises a filter (15) located in the passage (7) for absorbing emissions and a primary absorbent (17) located in the passage (7) immediately downstream of the filter (15) so that there are no voids between the filter (15) and the primary absorbent (17).

Description

SAMPLINGDEVICEFORAIRBORNEPARTICULATEORVAPOUREMISSIONS

The present invention relates to a device for sampling particulate and vapour emissions in occupational hygiene applications and to a method of analysing such emissions.

The term "particulate and vapour emissions" is understood herein to cover any emissions of potential interest, for example, from a personal occupational health view point including but not limited to compounds ranging between very volatile low molecular weight organics to high boiling point particulates and dusts.

The present invention is particularly suited although not limited to monitoring personal exposure to aromatic compounds including polycyclic aromatic hydrocarbon (PAH) emissions.

The Occupational Safety and Health Administration

(OSHA) and the National Institute for Occupational Safety and Health (NIOSH) sampling procedures are the existing procedures for sampling PAH emissions.

The OSHA procedure produces a result which is variously termed coal tar pitch volatiles (CTPV) , benzene soluble matter (BSM) , or benzene soluble fraction of total particulate matter (BSFTPM) . The last expression is usually reduced to benzene soluble fraction (BSF) . This value expresses the portion of particulate matter, sampled from the air by filtration, which is soluble in benzene. The sampling device for the OSHA procedure consists of a 37mm diameter glass fibre filter held in a polystyrene cassette. The sampling flow rate is nominally 2 L/min, which is achieved by the use of a small battery operated pump. The OSHA procedure is designed for measurement of personal exposure to the above substances.

There are well recognised inadequacies with this analytical procedure. The main problem is that any compounds with appreciable volatility are lost by evaporation from the filter during sampling. The research of the applicant has shown that one-half of the list of polycyclic aromatic hydrocarbons of environmental interest (the 16 U.S. EPA priority PAH) are affected in this way.

Furthermore, because of the distribution of these compounds in the environment, evaporative loss may account for 70- 80% of the total mass of these PAH emissions. It is well known that the OSHA procedure suffers from evaporative loss but existing standards of exposure to PAH emissions are based on OSHA results (expressed as CTPV or BSF) and OSHA is reluctant to change the sampling procedure.

NIOSH set out to improve the collection efficiency of the OSHA procedure by including an adsorbent-filled glass tube as a back-up behind the filter. The adsorbent prescribed is XAD-2, a styrene-divinylbenzene co-polymer. The procedure makes use of a Teflon (Registered Trade Mark) filter because of reported improvements in sampling efficiency compared to glass fibre filters. The filter is contained in a polystyrene cassette as in the OSHA procedure. The sampling flow rate is nominally 2 L/min. The filter is extracted with benzene - producing a BSF result - and the XAD-2 is extracted with a suitable solvent followed by chromatographic analysis of the compounds extracted. Although the NIOSH procedure represents an improvement over the OSHA procedure, there are still serious shortcomings associated with its use.

The research of the applicant has shown that pyrene is distributed in equal proportions between the filter and the back-up adsorbent. Pyrene is an important chemical because its analysis, in conjunction with that of 1-hydroxypyrene in urine, is used as an indicator of exposure to PAH emissions. However, the volatility of pyrene is low enough to cause it to condense on the inner walls of the sampling apparatus. In the NIOSH device, there is a relatively large surface area for condensation between the filter and the XAD-2 adsorbent and thus the potential for pyrene loss is appreciable. The materials of construction (polystyrene cassette and plastic connecting tubing) will not allow recovery of condensed pyrene by solvent washing.

A further weakness of the NIOSH procedure is its inability to allow measurement of very volatile compounds, such as benzene. The use of the NIOSH procedure necessitates a separate sampling exercise for these compounds.

Both the OSHA and NIOSH procedures recommend extraction of the filter by a relatively large volume (5 ml) of benzene. If the benzene solution is to be analysed by a chromatographic technique, evaporative concentration is required to give the necessary sensitivity to the analysis, and there is a strong possibility that the evaporative concentration will result in further loss of sampled components. Other analytical problems arise when the component concentration has been increased by evaporation of solvent .

An object of the present invention is to provide a device for sampling airborne emissions in the environment and a method of quantifying such emissions which alleviates the disadvantages of the OSHA and NIOSH sampling procedures described above in relation to polycyclic aromatic hydrocarbons.

According to the present invention there is provided a device for sampling airborne particulate or vapour emissions comprising: a passage having an inlet and an outlet, a filter means located in the passage for adsorbing emissions, and a primary adsorbent in the passage for emissions not adsorbed by the filter.

It is preferred that the device further comprises a pump means for pumping air through the passage.

It is preferred that the primary adsorbent be located immediately downstream of the filter so that there are no voids between the filter and the primary adsorbent.

It is preferred that the filter comprises glass fibre or Teflon.

It is preferred that the primary adsorbent comprises graphitised carbon.

It is preferred that the device be formed from a solvent resistant plastic material.

It is preferred that the device further comprises a secondary adsorbent in the passage downstream of the filter and the primary adsorbent for adsorbing emissions not adsorbed by the filter and the primary adsorbent. It is preferred particularly that the secondary adsorbent be charcoal.

It is preferred that the device comprises, a main sampler body, and a sampling head detachably coupled to the main sampler body, the sampling head defining the inlet of the passage.

With such an arrangement it is preferred that the main sampler body be adapted to receive the filter and that the filter be accessible when the sampling head is detached from the main sampler body.

With such an arrangement it is also preferred that the main sampler body be adapted to receive the primary adsorbent.

It is preferred that the device further comprises a sleeve detachably coupled to the main sampler body, the sleeve defining the outlet of the passage and being adapted to receive the secondary adsorbent.

It is preferred that the sampling head, the sampling body, and the sleeve be detachably coupled together by "quick-connect" or "twist-lock" fittings.

According to the present invention there is also provided a method of analysing airborne particulate or vapour emissions comprising:

(a) sampling the emissions with the device described in the preceding paragraphs; (b) separately extracting the filtered and adsorbed emissions from each of the filter, the primary adsorbent and, if used, the secondary adsorbent with, in each instance, a small volume of a solvent; and

(c) analysing each extracted solution by a capillary gas chromatograph using flame ionisation detection.

Typically, the small volume of the solvent is 200-400 μL.

It is preferred that the solvent be carbon disulphide.

It is preferred that the method further comprises mass spectrometric analysis of samples.

The present invention is described further by way of example with reference to the accompanying drawings in which:

Figure 1 is a schematic view of a preferred embodiment of a device for sampling particulate or vapour emissions in accordance with the present invention; and

Figure 2 is a schematic view of the device shown in Figure 1 in a disassembled form to illustrate the main components of the device.

The device 3 shown in the figures is adapted to be attached to a mounting plate 5 of a lapel clip so that it can be carried conveniently by persons exposed to an environment containing airborne emissions of interest. The device 3 comprises a passage, generally identified by the numeral 7, having an inlet 9 and an outlet 11. The outlet 11 is adapted to be coupled by means of a hose connector 13 and hose (not shown) to a pump (not shown) which is operable to draw air at a prescribed flow rate, typically 2 L/min, through the passage 7 from the inlet 9 to the outlet 11.

The device 3 further comprises, a filter 15 located in the passage 7 near the inlet 9 for adsorbing emissions of interest, a back-up primary adsorbent 17 in the passage 7 immediately downstream of the filter 15 for adsorbing emissions of interest that are not adsorbed by the filter 15, and a further back-up secondary adsorbent 19 in the passage 7 immediately downstream of the primary adsorbent 17 for adsorbing emissions of interest that are not adsorbed by the filter 15 and the primary adsorbent 17.

It is noted that the filter 15 prevents the primary adsorbent 17 escaping from the inlet 9 of the passage 7.

The device 3 further comprises, a retaining screen 31 which separates the primary adsorbent 17 and the secondary adsorbent 19, and a retaining screen 33 which prevents the secondary adsorbent 19 escaping from the outlet 11 of the passage 7.

The filter 15, the primary adsorbent 17, and the secondary adsorbent 19 may be formed from any suitable materials depending on the emissions of interest.

By way of example, in situations where the emissions of interest are organic, such as PAH, it is preferred that the filter 15 be formed from glass fibre or Teflon supported on a fine stainless steel support grid 37 (Figure 2) and that the primary and secondary adsorbents 17, 19 comprise graphitised carbon and charcoal, respectively.

It is preferred particularly that the charcoal be coconut charcoal.

It has been found that the combination of graphitised carbon and coconut charcoal is particularly useful because graphitised carbon has a very high capacity for retaining absorbed compounds and reduces the load on the charcoal, thus increasing the capacity of the charcoal to retain volatile species. In addition, it has been found that in conditions of high humidity the hydrophobic nature of the graphitised carbon surface allows its retention capacity to be maintained.

ith reference to Figure 2, the device 3 is formed from a number of components having "quick-connect" and "twist- lock" fittings for ease of assembly and disassembly of the device 3.

The components include a main sampler body 21 which is adapted to receive the filter 15 and the primary adsorbent 17, a sampling head 23 having a plurality of openings 25, typically 7, which define the inlet 9 of the device 3 and satisfy the SAA design criteria for inhalable dusts as specified in As 3640/1989, a sleeve 27 which is adapted to receive the secondary adsorbent 19, and the hose connector 13. The retaining screen 31 is connected to the sleeve 27 and the retaining screen 33 is connected to the hose connector 13. The sampler body 21, the sleeve 27, and the hose connector 13 comprise "quick-connect" couplings, and the sampling head 23 comprises a "twist-lock" coupling. The components of the device 3 may be formed from any suitable materials. It is preferred that the components be formed from Teflon or polypropylene for chemical inertness.

The ease of assembly and disassembly is an important consideration given that the filter 15 and primary and secondary adsorbents 17, 19 have to be removed periodically for extraction and analysis of filtered and adsorbed emissions of interest.

In this regard, in accordance with a preferred method of analysis, described hereinafter in relation to PAH from coke ovens as the emissions of interest, the filtered PAH emissions are extracted ultrasonically in a small (typically 1.0 mL) capped vial using a very small volume (typically 200-400 μD of carbon disulphide as a solvent. Similarly, the adsorbed PAH emissions are extracted separately from the primary and secondary adsorbents 17, 19 in 1 mL vials using small amounts of CS₂.

The extracted solutions are analysed by capillary gas chromatography (capillary GC) using flame ionisation detection. Instrument settings will vary depending on the type of GC used. In addition, a mass spectrometric analysis of samples could be used to characterise material being sampled, but this is desirable, not essential. A detection limit of 20-50ng/m³ should be routinely achievable, depending on the sophistication of analytical equipment. This limit may be lowered significantly by careful operation of both GC and data system.

The use of graphitised carbon as the preferred primary adsorbent 17 for PAH emissions allows CS₂ to be used in solvent stripping of the adsorbed PAH emissions. This is an advantage because CS₂ exhibits good solvency for aromatic compounds and its lack of FID response makes it ideal for use in GC analysis. The characterisation of the material being sampled by mass spectrometric analysis is not possible in the OSHA and NIOSH procedures.

In addition to its use for sampling coke oven emissions described previously, the device 3 and foregoing method of analysis are suitable for measuring PAH emissions from aluminium smelters and oil refineries, and preliminary results indicate it should be suitable for use in sampling environmental tobacco smoke. Thus, with appropriate adjustment of sampling time (to prevent overloading or to allow for very low concentrations of volatile organic compounds), the device 3 should be applicable to a wide variety of workplace environments. It is noted that in some cases it may be necessary to use a different solvent or even a displacing compound to ensure that compounds of interest are fully eluted from the adsorbent(s) .

The device 3 will also make it possible to seek a correlation between urinary metabolites of specific PAH emissions and occupational exposure to PAH emissions. Previous attempts to link urinary 1-hydroxypyrene with pyrene, when samples were collected by filter without any back-up, yielded poor correlation.

The device 3 can generate BSF results which agree with those from standard procedures (eg. OSHA) . The device 3 can replace the NIOSH sampling apparatus, being more rugged and compact and having the advantage of greater potential accuracy because the intimate contact (ie. no voids) between the filter 15 and the primary adsorbent allows no room for condensation. In particular, in the case of sampling PAH emissions this means that all the pyrene is recovered.

The device 3 is ideally suited to the monitoring of personal exposure to a wide range of particulate or vapour emissions including but not limited to, PAH emissions discussed previously, diesel exhaust emissions, vapours from paint-line operations, decomposition products from the heating of powdered paints, organic vapours evolved in road surfacing and in the production of aluminium, and vapour generated in the electrolytic production of manganese. The overall size, shape and mass is similar to current OSHA and NIOSH devices and so should be accepted readily be workers. The device 3 meets standard requirements of flow rate for inhalable dust sampling.

The following specific examples demonstrate the advantages of the device 3 over conventional standard procedures.

Example 1

An analysis of vapours evolved during "float and sink" operations at a coal testing laboratory.

The float and sink bath contained perchlorethylene, tetrabromoethane (TBE) and a light hydrocarbon distillate called "Ampol 143". The standard procedure for sampling tetrabromoethane (NIOSH 2003) recommends using silica gel tubes while charcoal is specified for perchlorethylene and the hydrocarbons. Charcoal cannot be used for sampling TBE because of a surface catalysed dehydrohalogenation of TBE to give tribromoethylene, a reaction which does not occur with either silica gel or graphitised carbon. Two separate sampling exercises are required to measure airborne concentrations of all the bath components when using standard procedures. It was found that a device 3 packed with graphitised carbon and charcoal successfully enabled analysis of all components from the one sample.

Example 2

The device 3 containing a PVC (GLA 5000) filter and silica gel adsorbent was used to collect mist generated from the electrolytic production of manganese.

The aim was to measure sulphuric acid and manganese sulphate together. During sampling, manganese sulphate and sulphuric acid both collect on the filter and some sulphuric acid passes through to the adsorbent. After sampling, dry air was drawn through the sampler to cause all the sulphuric acid (as S0₃) to evaporate from the filter and be collected on the adsorbent. The results obtained showed that all of the sulphate extracted from the filter was due to manganese sulphate and only sulphuric acid was found on the silica gel adsorbent. This was the first time that these two species had been successfully determined in combination in a single sample.

Example 3

The device 3 was used to sample fumes evolved during bake-out of the smelting cupola for aluminium production. The samples were analysed for the 16 U.S. EPA priority PAH compounds. The samples were collected alongside conventional NIOSH samplers which were set up according to NIOSH standard method 5516. The samples obtained by the NIOSH procedure were subject to component loss by breakthrough from the absorbent during high temperature sampling conditions. Specifically, there was component loss of 6 of the 16 compounds being measured (naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene and anthracene) in a significant number of samples from the NIOSH sampler. There was no breakthrough of these components in the device 3. In addition, data on vaporous aromatic hydrocarbons (benzene, toluene and xylene) was obtained, and there was no breakthrough of these volatile compounds. In addition, analysis for phenolic compounds and nitrogen-containing PAH was performed. Finally, the device 3 allowed a determination of BSF results as in the NIOSH standard.

Example 4

The device 3 was used to characterise fumes and vapours evolved during heating of paints. Two typical examples of this application are heating of powdered paint and welding of painted steel. The design of the device 3, incorporating a filter 15 and primary and secondary absorbents 17, 19 ensured successful sample collection, especially in the case of the welding operation were solids as well as vapours were evolved. There is no conventional or standard procedure which uses a single sampler for evolved components in these applications. It has been found possible to analyse both organic and inorganic material collected on the filter during sampling.

Many modifications may be made to the preferred embodiment of the device 3 without departing from the spirit and scope of the present invention. In this regard, whilst the preferred embodiment of the device 3 as shown in Figure 2 comprises a single sleeve 27 and retaining screen 31 which, when assembled, define a section for an adsorbent, it can readily be appreciated that the present invention is not so limited. Specifically, the device 3 may comprise two or more such sleeves which, when assembled, define a series of passages which may be filled as required by suitable adsorbents. By way of example, in the case of sampling PAH emissions, where the primary adsorbent 17 is graphitised carbon and the secondary adsorbent 19 is charcoal, it may be advisable to add a second charcoal section to avoid charcoal breakthrough problems caused by adsorption of water vapour. In such a situation the first charcoal section (the secondary adsorbent 19) retains all the water and some of the organics and the second charcoal section retains the remainder of the organics.

Claims

CLAIMS :

1. A device for sampling airborne particulate or vapour emissions comprising: a passage having an inlet and an outlet, a filter means located in the passage for adsorbing emissions, and a primary adsorbent in the passage for emissions not adsorbed by the filter.

2. The device defined in claim 1 further comprising, a pump means for pumping air through the passage.

3. The device defined in claim 1 or claim 2, wherein the primary adsorbent is located immediately downstream of the filter so that there are no voids between the filter and the primary adsorbent.

4. The device defined in any one of the preceding claims, wherein the filter comprises glass fibre or Teflon.

,

5. The device defined in any one of the preceding claims, wherein the primary adsorbent comprises graphitised carbon.

6. The device defined in any one of the preceding claims further comprising, a secondary adsorbent in the passage downstream of the filter and the primary adsorbent for adsorbing emissions not adsorbed by the filter and the primary adsorbent.

7. The device defined in claim 6, wherein the secondary adsorbent comprises charcoal.

8. The device defined in claim 6 or claim 7 further comprising, one or more further absorbents in the passage downstream of the filter and the primary and secondary absorbents for absorbing emissions not absorbed by the filter and the primary and secondary absorbents.

9. The device defined in any one of the preceding claims comprising, a main sampler body, and a sampling head detachably coupled to the main sampler body, the sampling head defining the inlet of the passage.

10. The device defined in claim 9, wherein the main sampler body is adapted to receive the filter and the filter is accessible when the sampling head is detached from the main sampler body.

11. The device defined in claim 10, wherein the main sampler body is adapted to receive the primary adsorbent.

12. The device defined in any one of claims 9 to 11 further comprising, a sleeve detachably coupled to the main sampler body, the sleeve defining the outlet of the passage and being adapted to receive the secondary adsorbent.

13. A method of analysing airborne particulate or vapour emissions comprising:

(a) sampling the emissions with the device described in any one of claims 1 to 12;

(b) separately extracting the filtered and adsorbed emissions from each of the filter, the primary adsorbent and, if used, the secondary adsorbent with, in each instance, a small volume of a solvent; and (c) analysing each extracted solution by a capillary gas chromatograph using flame ionisation detection.

14. The method defined in claim 13, wherein the small volume of the solvent is 200-400 μL.

15. The method defined in claim 13 or claim 14, wherein the solvent is carbon disulphide.

16. The method defined in any one of claims 13 to 15, further comprising mass spectrometric analysis of samples.

17. A method of analysing airborne particulate or vapour emissions substantially as herein described in Examples 1, 2 or 3.