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These procedures were designed and tested for internal use by OSHA personnel. Mention of any company name or commercial product does not constitute endorsement by OSHA.
|OSHA Permissible Exposure
|1 ppm Time Weighted Average (TWA)*
3 ppm Short-Term Exposure Limit (STEL)*
|Collection Device:||Passive badge monitor containing bisulfite-impregnated paper|
|Recommended Sampling Time:||8 h (4 to 16 h range)|
|Average Sampling Rate:||0.0614 ± 0.005 L/min (25°C & 760 mmHg)|
|Face Velocity:||Minimum 4.6 m/min (15 ft/min)|
|Analytical Procedure:||A modified chromotropic acid procedure is used. Sample filters are desorbed using deionized water. Solutions are acidified, and chromotropic acid is added. The color complex formed is analyzed using a UV spectrophotometer at 580 nm.|
0.039 ppm (4-h sampling time)
0.11 ppm (4-h sampling time)
|Dose Range:||0.8 to 72 ppm-h (as claimed by the manufacturer)|
|Precision and Accuracy|
|Validation Range:||0.2 to 4.9 ppm|
|Method Classification:||Validated Method|
|The 3M Model 3721 monitor is recommended for TWA determinations only. It is not recommended for STEL monitoring. Any samples taken for STEL determinations should follow OSHA method No. 52.|
|As compared to OSHA method no. ID-102.|
James C. Ku
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
OSHA Technical Center
Salt Lake City, Utah
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:
1. A water-saturated pad in the bottom section of the monitor has been added for sample humidification.
2. Each monitor is now packaged in a sealed metal container. Previously, the Model 3751 monitor was enclosed in a resealable plastic bag.
3. The calculated sampling rate has been changed from 0.0659 to 0.0614 L/min.
Note: The sampling rate of 0.0614 L/min is in agreement with a previous OSHA Salt Lake City Analytical Laboratory (SLCAL) study (5.5.).
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 laboratories (5.4.-5.6.). Results from these studies did not indicate serious problems with desorption efficiency, face velocity, reverse diffusion, or post-collection sample storage stability. The recent modifications instituted by 3M suggest sampling performance would not be significantly affected in these areas. As long as the face velocity of the sampled environment is above 4.6 m/min (15 ft/min), the sampling rate of the monitor does not appear to be significantly altered (5.4.-5.7.). Sampling and analytical procedures are identical for either model monitor; however, result calculations are different since slightly different sampling rates are used.
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 bisulfite-impregnated paper located within the assembly. The resulting adduct is desorbed with deionized water. An aliquot of the sample is reacted with chromotropic acid in the presence of sulfuric acid to form a purple mono-cationic chromogen. The absorbance of this colored solution is read in a spectrophotometer at 580 nm and is compared to prepared standards. Although the chemistry of the color formation is not well-established, the following reaction mechanism is proposed in acidic solution (5.8.):
1. The results of a storage stability test show that the mean recovery of samples stored after 30 days were within ±10% of the mean of monitors analyzed immediately after sampling.
2. The results of a face velocity test indicate that the 3M Model 3751 monitor canaccurately measure a known concentration as high as 10 ppm at face velocities as low as 15 ft/min.
3. The results of a sampling rate validation test indicate that the average sampling rate was 0.0614 ± 0.005 L/min.
4. The results of a reverse diffusion test indicate that reverse diffusion of collected formaldehyde from the monitor back into the atmosphere should not be a significant factor when sampling over an 8-h sampling period.
Dress goods store personnel
Electrical insulation makers
Embalming fluid makers
Ethylene glycol makers
Formaldehyde resin makers
Furniture dippers and sprayers
Glue and adhesive makers
Grease-resistant textile finishers
Lacquerers and lacquer makers
Oil well workers
Photographic film makers
Textile mordanters and printers
|Relative vapor density||1.043 (air = 1)|
|Solubility||Soluble in water, alcohol, and ether|
|Odor||Pungent and irritating|
|Explosive limits (Gas)||Gas 7.0-73% by volume in air|
|Flashpoint (closed cup)||50°C (122°F) of aqueous solution|
Note: Information listed within this section is a synopsis of current knowledge of the physiological effects of formaldehyde (HCHO) and is not intended to be used as the basis for OSHA policy.
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.):
|0.5 to 2 ppm||eyes, nose and throat irritation|
|3 to 5 ppm||tearing of the eyes|
|10 to 20 ppm||difficult breathing, nose and throat burning, cough, heavy tearing of the eyes|
|25 to 30 ppm||severe respiratory tract injury|
|100 ppm||immediately dangerous to life and health (IDLH)|
The 3M Model 3721 formaldehyde monitor (3M, St. Paul, MN) contains the following parts:
1) Container consisting of two aluminum cans held together by a label. The two cans are labeled can A and can B.
2) Can A contains:
Top Section (has a white film and plastic retaining ring),
Sealing Cup (has Date, Start Time, etc. written on it)
3) Can B contains:
Bottom Section (has a metal clip attached),
Translucent Closure Cap
Note: The original shipping container and aluminum cans can be reused for sample shipment to the lab.
1) Beginning sampling time
2) Sampling date
3) Monitor serial number
4) Employee or area identification
5) Temperature, pressure, and relative humidity at the sampling site
CAUTION: Formaldehyde has the potential to cause cancer in humans (5.12.). Extreme care must be observed when handling.
1. Sodium carbonate (Na2CO3), certified, 99.9% minimum purity: Dry the Na2CO3 powder at 120°C for 2 h, then transfer to a desiccator and cool to a constant weight. Use as a primary standard.
2. Sulfuric acid, 0.1 N: Dilute 3 mL of concentrated H2SO4 slowly to 1 L with DI H2O.
3. Sodium sulfite (Na2SO3), 12.5% (W/V): Dissolve 140 g of anhydrous Na2SO3 in 980 mL DI H2O. Store in a refrigerator (approximately 4°C).
1. Standardize the 0.1 N H2SO4 solution using the certified Na
2CO3 as a primary standard: Weigh 1.00 to 1.20 g of dried Na2
CO3 into a 250-mL beaker containing 50 mL of DI H2O, add 3 drops of methyl
red/bromocresol green indicator and titrate with the H2SO4 to a faint pink color.
Heat the titrated solution to a gentle boil for 2 min to expel any dissolved CO2, then cool the flask contents
to room temperature. If the end point has not been overrun, the indicator will reassume its characteristic green color. Complete the
titration with H2SO4 to a sharp color change. Calculate the normality of the H
2SO4 solution (N2) based on the following equation:
N2 = meq of Na2CO3/V2
V2 = mL of H2SO4 solution required to titrate the Na2CO3.
2. Use a pH meter and adjust the pH of 25.0 mL of the 12.5% Na2SO3 solution to 9.6 with the standardized 0.1 N H2SO4.
3. Place 50.0 mL of the HCHO ~1,000 µg/mL stock solution into a 250-mL beaker.
4. Add the previously adjusted Na2SO3 solution to the 250-mL beaker and titrate to a pH of 9.6 with the standardized 0.1 N H2SO4. Calculate the concentration of HCHO as follows:
HCHO, µg/mL =
A = mL of H2SO4 solution required to titrate the sample
B = mL of H2SO4 solution required to titrate the blank
C = normality of the H2SO4 solution (meq/mL)
D = (30 mg/meq of HCHO)(1,000 µg/mg)
= 30 × 103 µg/meq of HCHO
E = mL of formaldehyde used
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.
(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.)
(A)(sample vol, mL)(DF)
DF = Dilution Factor (if none, DF = 1)
ppm formaldehyde =
(W - Wb) × MV
MW × (AV)
AV = ST × 0.0614 × (T1 / T2)1.5 × (P2 / P1)
Wb = Total µg of formaldehyde in the blank sample
MV = Molar volume at 25°C and 760 mmHg (24.45 L/mole)
MW = Molecular weight of formaldehyde (30 g/mole)
ST = Sampling time (min)
0.0614 = Sampling rate (L/min) at 25°C and 760 mmHg
T1 = Sampling site temperature (K)
T2 = 298 K
P1 = Sampling site pressure (mmHg)
P2 = 760 mmHg
Report results to the industrial hygienist as ppm formaldehyde.
See Reference 5.9. for complete information.
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