Occupational hygiene standard for tetrachloroethylene in workshop air
Release Time:
2010-10-25 09:33
Source:
China Laundry Information Center
1. Subject Matter and Scope of Application
This standard specifies the maximum allowable concentration of tetrachloroethylene in workshop air and its monitoring and inspection methods.
This standard applies to all types of enterprises producing and using tetrachloroethylene.
2. Hygiene Requirements
The maximum allowable concentration of tetrachloroethylene in workshop air is 200mg/m³.
3. Monitoring and Inspection Methods
The monitoring and inspection method of this standard uses gas chromatography, see Appendix A (Supplement).
4. Supervision and Enforcement
Health supervision agencies at all levels are responsible for the enforcement of this standard.
Appendix A
Gas Chromatography Method
(Supplement)
A1 Principle
A1.1 Collect tetrachloroethylene in the air using activated carbon tubes, thermally desorb and inject the sample, separate by polyethylene glycol 6000 column, detect with hydrogen flame ionization detector, qualitative by retention time, quantitative by peak height.
A1.2 The detection limit of this method is 1.8×10⁻² μg (direct injection of 1mL desorbed gas sample).
A2 Instruments
A2.1 Activated carbon tube: glass tube 200mm long, inner diameter 3.5–4.0mm, outer diameter 6mm, packed with 100mg 20–40 mesh coconut shell activated carbon, fixed at both ends with a small amount of silanized glass wool. Before packing, treat activated carbon with nitrogen at about 300°C for 3–4 hours; after packing, blow with nitrogen at the same temperature for 2–3 minutes. For short-term use, cover both ends with plastic caps; for long-term use, seal both ends by fire.
A2.2 Sampling pump, 0–1L/min.
A2.3 Syringes: 100mL, 5mL, 1mL, 1μL.
A2.4 Thermal desorption device: mainly consists of electric heater, temperature controller, thermometer, and gas flow controller. Flow control range is 50–100mL/min. The structure should allow easy insertion of the activated carbon tube into the heater and ensure the gas passing through the tube is preheated and the activated carbon is evenly heated.
A2.5 Gas chromatograph: hydrogen flame ionization detector.
A3 Reagents
A3.1 Tetrachloroethylene, analytical grade.
A3.2 Polyethylene glycol 6000, chromatographic stationary phase.
A3.3 6201 red carrier, 60–80 mesh.
A3.4 Anhydrous methanol, analytical grade.
A3.5 Dichlorodimethylsilane, analytical grade.
A4 Sampling
Open the activated carbon tube at the sampling site, with both ends having an aperture of at least 2mm, place vertically, and draw 1–2L of air at a speed of 0.2–0.5L/min. After sampling, cover both ends with plastic caps and analyze as soon as possible.
A5 Analysis Steps
A5.1 Chromatographic Conditions
a. Chromatographic column: 2m long, 3mm inner diameter glass column, polyethylene glycol 6000: 6201 red carrier = 5:100, column temperature: 90°C;
b. Vaporization chamber temperature: 150°C;
c. Detector temperature: 150°C;
d. Carrier gas (nitrogen): 60mL/min.
A5.2 Standard Curve Preparation
Accurately measure a certain amount of tetrachloroethylene with a micro syringe (at 20°C, 1μL tetrachloroethylene weighs 1.6227mg), inject into a 100mL syringe to prepare standard gases of 0.175, 0.350, 0.700, 1.75μg/mL, respectively. Take 1mL for injection, measure peak height and retention time. Repeat 3 times for each concentration, average the peak heights, plot peak height against tetrachloroethylene content to draw the standard curve. Retention time is used as qualitative indicator.
A5.3 Sample Analysis
A5.3.1 Control test: bring the activated carbon tube to the site, bring it back to the laboratory with the sample, analyze as the sample, used as blank control.
A5.3.2 Sample treatment: connect the sample tube inlet to a 100mL syringe, place on the thermal desorption device, desorb at 250°C with nitrogen at 50–60mL/min, desorbed gas volume is 100mL.
A5.3.3 Measurement:
Inject 1mL of desorbed gas, qualitative by retention time, quantitative by peak height, chromatogram shown in Figure A1.
A6 Calculation
Where: X — concentration of tetrachloroethylene in air, mg/m³;
C — concentration of tetrachloroethylene obtained from the standard curve, μg/mL;
V₀ — sampling volume converted to standard conditions, L.
A7 Precautions
A7.1 When tetrachloroethylene concentrations are 0.175, 0.350, 0.700, 1.75μg/mL, the coefficients of variation are 4.1%, 4.5%, 2.8%, and 2.1% respectively; the breakthrough capacity of 100mg activated carbon tube test is greater than 43mg.
A7.2 Activated carbon tubes adsorb almost all organic vapors. After sampling, both ends should be immediately sealed with plastic caps to prevent contamination. Samples can be stored at room temperature for 14 days without loss, but generally should be analyzed as soon as possible.
A7.3 When applying the thermal desorption method, the desorption efficiency must be tested first. It can only be applied if the desorption efficiency is above 75%. In this study, the desorption efficiency ranged from 87.5% to 94.4%.
Additional Notes:
This standard is proposed by the Ministry of Health of the People's Republic of China.
This standard was drafted by the Beijing Institute of Labor Hygiene and Occupational Disease Prevention and Control, in collaboration with the Haidian District Health and Epidemic Prevention Station of Beijing.
The main drafter of this standard is Dai Riying.
This standard is interpreted by the Institute of Labor Hygiene and Occupational Diseases, Chinese Academy of Preventive Medicine, the technical authority entrusted by the Ministry of Health.
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