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FORMALDEHYDE IN WORKPLACE ATMOSPHERES
Commercial manufacturers and products mentioned in this method are for descriptive use only and do not constitute endorsements by USDOL-OSHA. Although the following sampling procedure uses a specific formaldehyde monitor, other passive monitors can be substituted provided they meet validation requirements.
Branch of Inorganic Methods Development
This method describes the passive monitor collection of airborne formaldehyde in the breathing zone of workplace personnel and the subsequent analysis of those samples using a colorimetric technique. Although this method specifically mentions the 3M Model 3721 monitor, other monitors can be used provided performance requirements have been met. Some examples of validation procedures to determine performance are given in references 5.1. and 5.2.
The simplicity and freedom of the 3M Model 3751 formaldehyde passive monitor showed promise when first offered in 1981 as an industrial hygiene sampling alternative for formaldehyde (5.3.); however, subsequent independent studies indicated analyte loss when sampling at low humidities (5.4., 5.5.). Consequently, the Model 3751 monitor was removed from the market by 3M in April, 1984. The Model 3721 3M monitor, capable of sample humidification, was introduced in 1985 as a replacement. The changes instituted by 3M and incorporated into the model 3721 are:
With the exception of the moisturizing pad, the appearance of the
Model 3721 is physically identical to the Model 3751 monitor. The
Model 3751 monitor has been extensively evaluated by independent
The 3M formaldehyde monitor is a diffusion-type air monitoring
assembly worn near the breathing zone of personnel to evaluate
potential exposure to formaldehyde (HCHO) vapors. Formaldehyde vapor
is adsorbed on
1.3. Advantages and Disadvantages
1.3.2. The passive dosimeter used for collection of formaldehyde vapor is small, lightweight, and requires no sampling pumps.
1.3.3. The collected formaldehyde sample is stable for at least 30 days.
1.3.4. One disadvantage of the method is that the analytical procedure may not be capable of accurately determining STEL exposures at or below 3 ppm.
1.3.5. Another disadvantage with the dosimeter is sample rate dependence on face velocity. The dosimeter should not be used in areas where the air velocity is less than 4.6 m/min (15 ft/min). Most industrial work areas have air movement above 7.6 m/min (25 ft/min).
1.3.6. A disadvantage concerning the analytical procedure is the use of concentrated H2SO4 during sample preparation. Extreme care should be used when handling H2SO4.
1.4. Method Performance (5.5., 5.9.)
1.4.2. The coefficient of variation
(CVT) for the total analytical and
sampling method (50% RH) was 0.084. The overall error (as compared
to the reference method OSHA
1.4.3. The qualitative detection limit of the analytical method
is 0.7 µg of formaldehyde based on a
1.4.4. The quantitative determination limit for the analytical
method is 2 µg of formaldehyde in a
1.4.5. Somewhat variable results were obtained when sampling for
a short duration (STEL). Therefore, the 3M Model 3721 monitor is
recommended for 4 to
1.4.6. The Model 3751 monitor was extensively evaluated in 1982 (5.5.) and included storage stability, face velocity, sampling rate, and reverse diffusion experiments. Due to the similarity of the 3751 and 3721 monitors, these experiments were not repeated for the Model 3721. The 3751 experiments indicated (5.5.):
1.5.2. Any compound that has the potential of developing the same color as the formaldehyde/chromotropic acid complex using the conditions described in this method is an interference.
1.5.3. It has been reported by 3M that there is no interference from phenol (5.10.). The lack of interference is mainly due to the monitor's inability to collect a significant amount of phenol.
1.6. Uses (5.11.)
1.6.2. Potential occupational exposures to formaldehyde are listed:
1.7. Physical Properties (5.11.):
Formaldehyde is considered a strong irritant and potent sensitizer. Inhalation of large amount of HCHO can cause severe irritation of the upper respiratory tract and death. Data from human exposures indicate that exposure to large concentrations of HCHO gas may lead to pulmonary edema. Even HCHO gas present in the workroom at concentrations of 1 to 11 ppm can cause eye, nose, and throat irritation (5.11.). Formaldehyde has the potential to cause cancer in humans (5.12.).
The following symptoms have been noted in some individuals (5.12.):
2.1.2. If the possibility exists that the face velocity of an area being sampled is less than 4.6 m/min (15 ft/min), an active sampling device (i.e. OSHA sampling and analytical method No. 52) should be used instead of the passive monitor.
2.2. Equipment - Passive Monitors (If provided, also follow the 3M Formaldehyde Monitor Model 3721 - Instructions for Use.)
The 3M Model 3721 formaldehyde monitor (3M, St. Paul, MN) contains the following parts:
2.2.2. Remove the Translucent Closure Cap from the Bottom Section. Save the Closure Cap.
2.2.3. Pressing firmly, snap together the Top and Bottom Sections. Make sure the white film and plastic ring are NOT removed from the Top Section. The monitor is now ready for sampling.
2.3. Sampling Procedure
2.3.2. Record the following information:
1) Beginning sampling time
2.3.3. If possible, sample for 8 h. The minimum sampling time recommended is 1 to 2 h. For indoor air quality investigations, sample up to 16 h.
2.3.4. Immediately after sampling, remove and discard the white plastic film and purple retaining ring from the monitor. In place of the film/ring, snap on the Translucent Closure Cap by applying some pressure. A "clicking" sound should be heard when the cap is securely fastened.
2.3.5. Be sure both plugs on the Translucent Closure Cap are
firmly seated. This will insure a
2.3.6. Snap the Sealing Cup into place on the Bottom Section of the monitor. Be sure the cup is snapped securely.
2.3.7. Record the end sampling time and any drastic change (>10%) in temperature, pressure, or relative humidity that may have occurred during sampling.
2.3.8. Assemble a blank sample in the same fashion as mentioned
2.4. Sample Shipment
2.4.2. Submit at least one blank sample with each set of samples. The blank sample should have been handled in the same manner as the other samples except that it was not exposed. If possible, also submit a "lot blank". This is an unused monitor inside an unopened aluminum container.
2.4.3. When other substances are known or suspected to be present in the air, such information should be transmitted with the sample.
2.4.4. Send the monitors directly to the laboratory and request formaldehyde analysis. The original shipping carton can be used for shipment.
3.1.2. Observe laboratory safety regulations and practices.
3.1.3. CAUTION: Sulfuric acid can cause severe burns. Wear protective gloves, labcoat, and eyewear when handling concentrated sulfuric acid and the formaldehyde stock solution.
CAUTION: Formaldehyde has the potential to cause cancer in humans (5.12.). Extreme care must be observed when handling.
3.1.4. Do not store formaldehyde standards or samples in a refrigerator since polymerization will occur. Polymer precipitation may be observed by the appearance of a white milky substance in the formaldehyde solution.
3.1.5. Sodium sulfite solutions used for formaldehyde standardization gradually absorb carbon dioxide on exposure to air. Solutions which have stood for more than a week should be discarded.
3.1.6. Do not use reagent bottles having caps which contain phenolic resins. Formaldehyde contamination could occur.
3.2.2. Meter, pH.
3.2.3. Miscellaneous volumetric glassware or plasticware: Volumetric burets, graduated cylinders, pipettes, volumetric and Erlenmeyer flasks, other laboratory glassware, syringes. (Note: All glassware or plasticware should be washed and rinsed thoroughly with deionized water and then air dried prior to use.)
3.2.4. Analytical balance (0.01 mg).
3.3. Reagents (All chemicals should be reagent grade or better.)
3.3.2. Chromotropic acid sodium salt
solution (1%): Dissolve 1 g of chromotropic acid sodium salt
3.3.3. Sulfuric acid (H2SO4), concentrated.
3.3.4. Sodium bisulfite (NaHSO3), 1%: Dissolve 10 g of NaHSO3 in 1 L of DI H2O.
3.3.5. Formaldehyde (HCHO) solution, 37%.
3.3.6. Formaldehyde stock solution, ~1,000 g/mL: Dissolve 2.7 g (about 3 mL) of 37% HCHO solution in 1 L of DI H2O. Standardize this solution as described in Section 3.4. The solution is stable for at least 6 months. (Note: After 6 months, the standardization should be repeated).
3.3.7. Reagents for standardization of HCHO stock solution:
3.4. Standard Preparation
3.4.2. Preparation of standards
To a series of 25-mL Erlenmeyer flasks already containing 2 mL of 1% NaHSO3, carefully add 1.0, 3.0, 5.0, 10.0, 15.0, and 20.0 µL of the ~1,000 µg/mL HCHO stock solution. If the stock solution is prepared as exactly 1,000 µg/mL HCHO after standardization, these aliquots are equivalent to 1.0, 3.0, 5.0, 10.0, 15.0, and 20.0 µg of HCHO. As an alternative, standards can be prepared in 1% NaHSO3 using serial dilution of the ~1,000 µg/mL stock solution.
3.5. Sample Preparation
3.5.2. Open both ports of the Translucent Closure Cap of each monitor.
3.5.3. Using the center port of the Translucent Closure Cap and a small pipette or syringe, add 3 mL of DI H2O to each monitor. Reseal the ports.
3.5.4. After 30 min, with occasional gentle agitation, transfer a
2-mL aliquot of the solution into a
(Note: Add the sulfuric acid slowly and carefully. Add H2SO4 to the samples and standards in the same fashion since heat catalyzes the color formation.)
3.6.2. Allow the solutions to cool to room temperature, then
measure the absorbance of each solution at 580 nm using a
3.6.3. If the sample absorbance is larger than the absorbance of
the highest standard, take a smaller aliquot from the monitor,
dilute to 2 mL, and repeat Sections
3.7.2. Determine the amount (µg) of formaldehyde, A, corresponding to the absorbance in each analyzed sample aliquot from this curve.
3.7.3. Calculate the total amount (µg) of formaldehyde, W, in each sample:
3.7.4. Blank correct each sample and calculate the concentration of formaldehyde in each sample:
AV = ST × 0.0614 × (T1 /
T2)1.5 × (P2 / P1)
3.8. Reporting Results
Report results to the industrial hygienist as ppm formaldehyde.
See Reference 5.9. for complete information.
5.2. Occupational Safety and Health Administration Analytical
Laboratory): "Precision and Accuracy Data Protocol for Laboratory
Validations" or "An Outline for the Evaluation of Organic Sampling and
Analytical Methods". In The OSHA Laboratory Methods Manual.
Cincinnati, OH: American Conference of Governmental Industrial
Hygienists (Pub No. ISBN:
5.3. Rodriguez, S.T., P.B. Olson, and V.R. Lund: "Colorimetric Analysis of Formaldehyde Collected on a Diffusional Monitor." Paper presented at Amer. Ind. Hyg. Assoc. Conference, Portland, OR, May 1981.
5.4. Kennedy, E.R. and R.D. Hull: Evaluation of the Du Pont
Pro-Tek Formaldehyde Badge and the 3M Formaldehyde Monitor. Amer.
Ind. Hyg. Assoc. J.
5.5. Occupational Safety and Health Administration - Salt Lake
City Analytical Laboratory
5.6. National Council of the Paper Industry for Air and Stream Improvement Inc. (NCASI): A Laboratory Evaluation on the Performance of Passive Diffusion Badge Monitors and Detector Tubes for Determination of Formaldehyde. (Technical Bulletin No. 451). NY: NCASI, 1985.
5.7. Occupational Health and Safety Products Division/3M: 3M Brand Formaldehyde Monitor #3750/3751. St. Paul, MN: 3M Company, Internal document - No publication date given.
5.8. Feigl, Fritz: Spot Tests in Organic Analysis. 7th Ed. NY: American Elsevier Publishing Co., 1966.
5.9. Occupational Safety and Health Administration Technical
Center: Evaluation of 3M Formaldehyde Monitors (Model 3721)
by J.C. Ku and E.F. Zimowski
5.10. 3M Company: Research Report for 3M Formaldehyde Monitor, St. Paul, MN: 3M Company, Internal document - No publication data given.
5.11. National Institute for Occupational Safety and Health:
Criteria for a Recommended Standard - Occupational Exposure to
Formaldehyde. (DHEW/NIOSH Pub. No.
5.12. "Formaldehyde" Code of Federal Regulations 29CFR
1910.1048. 1989. pp
5.13. Blaedel, W.J. and V.W. Meloche: Elementary Quantitative Analysis. New York, NY.: Harper & Row, 1963. pp. 366
5.14. Burlington Industries: Standard Test Method for the Determination of Latent Formaldehyde, Burlington Industries Chemical Division, Internal document - No publication data given.