FLUORIDE (F¯ and HF) IN WORKPLACE ATMOSPHERES
| Method Number: | ID-110 |
| Matrix: | Air, Wipe (Smear Tabs for particulate fluoride) |
| OSHA Permissible Exposure Limits Final Rule Limits Fluorides (as F): Hydrogen Fluoride: |
2.5 mg/m3 Time Weighted Average (TWA) 3 ppm TWA 6 ppm Short-Term Exposure Limit (STEL) |
| Transitional Limits | |
| Fluoride Dust (as F): | 2.5 mg/m3 TWA |
| Hydrogen Fluoride: | 3 ppm TWA |
| Collection Procedures | |
| Fluorides: | A known volume of air is drawn through a cassette containing a mixed-cellulose ester (MCE) filter and backup pad using a calibrated personal sampling pump. |
| Hydrogen Fluoride: | A known volume of air is drawn through a
|
| Recommended Air Volumes: | |
| TWA Determinations | 90 L |
| STEL Determinations | 22.5 L |
| Recommended Sampling Rate: | 1.5 L/min |
| Analytical Procedure: | Filters (MCE) are fused with sodium hydroxide, and treated
|
| Detection Limit Quantitative: |
25 µg (25-mL sample solution volume) |
| Precision and Accuracy Validation Range: |
350 to 700 µg load (as HF) |
| CV1 | 0.057 |
| Bias | -0.01 |
| Overall Analytical Error | ±12.4% |
| Method Classification: | Validated Analytical Method |
| Date (Date Revised): | December 1988 (Feb. 1991) |
Commercial manufacturers and products mentioned in this method are for descriptive use only and do not constitute endorsements by USDOL-OSHA.
Similar products from other sources can be substituted.
Division of Physical Measurements and Inorganic
Analyses
OSHA Technical Center
Salt Lake City, Utah
1. Introduction
This method describes the collection and analysis of airborne hydrogen
fluoride or particulate
- 1.1. History
In the past, samples for determination of particulate and gaseous
fluoride compounds were collected using the sampling procedure
mentioned in this method with one exception. For HF sampling, the MCE
filter was previously placed on the
1.2. Principle
An air sample is taken by drawing a known amount of air through a
cassette containing a
The MCE filter containing particulate fluoride is fused with sodium
hydroxide to facilitate solubility of the particulate. The resulting
alkali flux is dried, neutralized with hydrochloric acid, and then
diluted to a specified volume with deionized water. The sodium
1.3. Advantages and Disadvantages
- 1.3.1. This method is a simple sampling and analytical procedure
able to detect fluoride over a large concentration range.
1.3.2. Analytical interferences are minimized by the addition of a buffer and use of the standard additions technique. Ions commonly associated with fluoride in work atmospheres (i.e. chloride, bromide, iodide, sulfate, nitrate, phosphate, and acetate) do not interfere with the analysis.
1.3.3. The instrumentation and sample preparation are inexpensive.
1.3.4. A disadvantage of this method is the sample preparation which involves a tedious sample flux technique.
1.3.5. Another disadvantage is the tendency for ISE readings to drift when measuring low concentrations.
1.4. Physical and Chemical Properties (8.1.)
Some properties and additional information regarding hydrogen
fluoride are listed below. Particulate fluoride compounds are too
numerous to describe; sodium fluoride (NaF) is included below as an
example of a soluble
| Synonyms | (HF) | Hydrofluoric acid, hydrogen fluoride |
| (Fluoride) | Variety of compounds, fluoride ion, perfluoride | |
| CAS no. | (HF) | 7664-39-3 |
| (Fluoride) | 16984-48-8 | |
| (NaF) | 7681-49-4 | |
| Physical properties | (HF) | Colorless, fuming mobile liquid. Attacks glass and any
|
| (NaF) | Clear crystals or white powder | |
| Boiling Point | (HF 38% solution) | 112 °C |
| (HF) | 19.5 °C | |
| (NaF) | 1695 °C | |
| Density | (HF) | 0.988 (liquid @ 14 °C) |
| (NaF) | 2.558 (14 °C) | |
| Solubility | (HF) | Soluble in water |
| (NaF) | Soluble in water | |
| Physiologic effect | (HF) | Strong irritant to eyes, skin, and mucous membranes. Toxic by inhalation or ingestion. |
| (NaF) | Tissue irritant, toxic by inhalation or ingestion. | |
| Uses | (HF) | Aluminum production, fluorocarbons, stainless steel pickling, glass etching, oil well acidizing, gasoline production, uranium processing. |
| (NaF) | Water fluoridation (~ 1 ppm), degassing steel, fungicide and rodenticide, wood preservative, electroplating, toothpaste additive, glass manufacture, disinfectant (in fermentation), dental prophylaxis. |
2. Range and Detection Limit
The analytical range is from 25 to 2,000 µg fluoride. Samples larger than 2,000 µg can be diluted and analyzed. An estimated detection limit of 25 µg is used. This detection limit is based on the lowest concentration standard used in the analysis.
3. Method Performance
Quality control data (8.2.) from the OSHA Technical Center (OSHA-SLTC) indicate an average recovery of 99% with a coefficient of variation of 0.057 for 60 samples spiked with sodium fluoride. The overall analytical error for these quality control samples (analyzed from 1986 to 1990) was ±12.4%. Factors which may influence precision and accuracy include electrode temperature, drift, and noise.
The sampling portion of the method had previously been evaluated at a flow rate of 1.5 L/min (see reference 8.3. for more information).
4. Interferences (Analytical) (8.4.)
Interference due to OH¯ ion can be controlled by maintaining the pH
between 4.5 and 10.5. Loss of fluoride from complex formation of fluoride
ion with polyvalent cations is controlled by the addition of a buffer
during analysis. Interferences can further be minimized using a standard
additions technique. Formation of HF and HF¯ at low pH is avoided by using
a sample matrix having a
5. Sampling
- Forceps
- Pipets, 0.5 mL
- Sodium carbonate (Na2CO3)
- Glycerol (C3H8O3)
- Impregnation solution
[Na2CO3
solution with glycerol]
- prepare by dissolving 4.0 g Na2CO3 in 50 mL deionized water, add 2 mL glycerol, and dilute this solution to 100 mL with deionized water.
- 5.1. Equipment - Air Samples (Note: Any chemicals used
in sampling media preparation should be reagent grade or better)
- 5.1.1. Particulate collection: Mixed cellulose
ester (MCE) filters (0.8 µm pore size), cellulose backup pads for
filter support, and two- or
5.1.2. Particulate and hydrogen fluoride collection:
In addition to the MCE filter, a filter spacer (Cat. No.
Using a forceps, remove the MCE filters from the three-piece cassettes and use the opened cassettes as supports for backup pad impregnation. Each backup pad should be resting on the ridge of the middle insert of the cassette and not in contact with the cassette base when impregnating.
Slowly pipet 0.5 mL of the impregnation solution over the entire backup pad and let dry overnight. Assemble the cassettes such that the backup pad resides in the lower section (the cassette outlet), and the MCE filter and filter spacer is in the upper section (the inlet) as shown:
Use the treated backup pads within 2 months of preparation.
5.1.3. Gel bands (Omega Specialty Instrument Co., Chelmsford, MA) for sealing cassettes. Seal cassettes with the bands after assembly.
5.1.4. Sampling pumps capable of sampling at 1.5 liters/min (L/min) with less than ±5% pump error.
5.1.5. Assorted flexible tubing.
5.1.6. Stopwatch and bubble tube or meter for pump calibration.
5.2. Equipment - Wipe Samples
- 5.2.1. Smear tabs (part no. 225-24, SKC Inc., Eighty Four, PA).
5.2.2. Deionized water.
5.2.3. Scintillation vials, 20-mL (part no. 74515 or 58515,
Kimble, Div. of
5.3. Sampling Procedure - Air Samples (Also see note in Section 7.3.)
- 5.3.1. Connect sampling media for calibration purposes to each
pump and calibrate to approximately 1.5 L/min.
5.3.2. Remove the calibration media and connect the appropriate sampling media to each pump. For particulate fluoride sampling only, use the media described in Section 5.1.1. For HF and particulate fluoride, use the media listed in Section 5.1.2. Make sure the filter cassette is connected to the pump with flexible tubing such that sampled air enters the MCE filter first.
5.3.3. Place the sampling assembly on the employee or workplace area so it does not interfere with the work being performed.
5.3.4. Collect air samples at a flow rate of 1.5 L/min. Whenever possible for TWA measurements, take consecutive samples for 1 h each. Take enough samples to cover the entire workshift. Observe each cassette during sampling to make sure the filter does not become overloaded.
5.3.5. Take samples for at least 15 minutes for STEL measurements. The minimum suggested total air volume for STEL determinations is 22.5 L.
5.3.6. Replace the end plugs into the filter cassettes immediately after sampling.
5.3.7. Securely wrap each sample cassette end-to-end with an OSHA Form 21 sample seal.
5.4. Sampling Procedure - Wipe Samples
- 5.4.1. Wear clean, impervious, disposable gloves when taking
each wipe sample.
5.4.2. Moisten the wipe filters with deionized water prior to use.
5.4.3. If possible, wipe a surface area covering 100 cm2.
5.4.4. Fold the wipe sample with the exposed side in.
5.4.5. Transfer the wipe sample into a 20-mL scintillation vial
and seal with vinyl or electrical tape. Securely wrap an
5.5. Shipment
- 5.5.1. Document the operation sampled and record other chemical
substances in use.
5.5.2. Request fluoride analysis. Also request hydrogen fluoride analysis if the impregnated backup pad was used. For smear tabs, only total particulate fluoride will be analyzed and reported.
5.5.3. Submit at least one blank sample with each set of air or wipe samples. The blank sample should be handled in the same manner as the other samples except that an actual sample is not taken.
5.5.4. Ship the samples to the laboratory for analysis as soon as possible in a suitable container designed to prevent damage in transit.
6. Analysis
- Carefully remove each filter from it's cassette using a
forceps. Place each filter in a separate, labeled
75-mL nickel or monel crucible. Record the crucible number in a log book next to the appropriate sample number. Using an automatic or glass volumetric pipet, carefully add 5 mL of 5 N NaOH to each crucible. - Turn on the vacuum-assisted drying oven. Place the heat setting to maintain a drying temperature of 140 °C (Note: For the equipment mentioned in Section 6.2.6., 140 °C is approximately 85% of the maximum setting). Place the samples on a metal tray and secure with tape to prevent the crucibles from "walking" off the surface due to vibration. Place the tray containing the samples on the bottom of the drying oven. Close the oven door tightly and dry for 1 h at 140 °C.
- Before proceeding, make sure the drying oven air vents are open to the surrounding atmosphere. Turn on the vacuum to the drying oven and then close the vents. Continue drying with the vacuum on for an additional hour. When drying is complete, open the oven air vents. When the vacuum reaches 10 mmHg or less, close off the vacuum. Open the oven door when the internal oven pressure is equal to ambient atmospheric pressure. Carefully remove the tray of samples and turn off the oven.
- Place dried samples in a desiccator until the next step (5) is performed, since the samples will reabsorb moisture from the air.
- In an exhaust hood, fuse the samples with the added NaOH by
carefully heating the crucible over a Bunsen burner and slowly
swirling the molten NaOH around the inside of the crucible.
Note: If splattering occurs, place the crucibles back into the oven for more complete drying.
- Allow the samples to cool, then add 10 mL DI H2O to each crucible.
- Carefully add 1.5 to 2 mL of concentrated HCl to neutralize the basic solution.
- Quantitatively transfer the contents of each crucible into
separate
25-mL volumetric flasks and dilute to volume with DI H2O.
- 6.1. Safety Precautions
- 6.1.1. All work with concentrated acids or bases is potentially
hazardous. Always wear safety glasses and protective clothing.
6.1.2. Prepare all fusions in an exhaust hood.
6.1.3. Care should be exercised when handling any acidic or basic solutions. If any acid or base contacts the eyes, skin, or clothes, flush the area immediately with copious amounts of water. Medical treatment may be necessary. Acid or base contact with work surfaces should be avoided.
6.1.4. Use a pipet bulb, never pipet by mouth.
6.1.5. Before using any instrument, the operator should consult the Standard Operating Procedure (SOP) (8.5.) and any instrument manuals.
6.2. Equipment
- 6.2.1. Ion Specific Electrode (ISE) and filling solution,
fluoride (Model
6.2.2. Electrode, pH and filling solution (Model 81-02 RossTM Combination pH electrode, Orion Research Inc.).
6.2.3. Reference electrode and filling solution (Model 90-01, Orion Research Inc.).
6.2.4. Millivolt/pH meter, capable of relative mV, pH, standard addition or concentration measurements (Model EA 940 Expandable Ionanalyzer, Orion Research Inc.).
6.2.5. Stirrer, electronic, or magnetic with Teflon stirring bars.
6.2.6. Drying oven, vacuum-assisted (Model 5851, National Appliance Co., Portland, OR).
6.2.7. Nickel or monel crucibles, 75-mL.
6.2.8. Laboratory glassware including 25-, 250-, 500-, and 1,000-mL volumetric flasks, and various sizes of Class A volumetric pipets.
6.2.9. Polyethylene beakers, 100-mL.
6.2.10. Forceps.
6.2.11. Desiccator.
6.2.12. Eyedroppers or disposable Pasteur pipets.
6.2.13. Automatic pipets, adjustable, 0.1- to 5.0-mL range
(models
6.2.14.Analytical balance (0.01 mg).
6.3. Reagents (All chemicals should be reagent grade or better)
- 6.3.1. Deionized water (DI H2O).
6.3.2. Sodium hydroxide (NaOH) pellets.
6.3.3. Sodium hydroxide, 5 N: Dissolve 200 g NaOH pellets
in approximately 600 mL of DI H2O and
dilute to
6.3.4. Sodium hydroxide, dilute: 0.5 and 0.05 N for pH adjustments.
6.3.5. Sodium fluoride (NaF).
6.3.6. Sodium fluoride stock solution, 1,000 µg/mL as F¯:
Dissolve 2.2105 g NaF in DI H2O and dilute
to
6.3.7. Tris(hydroxymethyl)aminomethane [(CH2OH)3CNH2].
6.3.8. Hydrochloric acid (HCl), concentrated (36.5 to 38% w/w).
6.3.9. Hydrochloric acid, dilute (2%) for pH adjustments.
6.3.10. Sodium tartrate (Na2C4H4O6· 2H2O).
6.3.11. Tris-Tartrate (T-T) buffer (concentrated): To
approximately 500 mL DI H2O add 84 mL of
concentrated HCl, 242 g tris(hydroxymethyl)aminomethane and 230 g
sodium tartrate. Stir to dissolve and let cool to room temperature.
Dilute to
6.3.12. Tris-Tartrate (T-T) buffer (analytical): Dilute 360 mL of
concentrated
6.3.13. 1:1 T-T buffer/DI H2O (for
dilutions only): Dilute equal volumes of analytical
6.3.14. Buffer solutions, in the range of pH 4 to 10.
6.4. Standard Preparation
Prepare dilutions of the 1,000 µg/mL F¯ stock standard. Use DI H2O as the diluent and store all standards in polyethylene bottles. An example of preparation of three standards in the analytical working range is shown:
| Standard | Dilution of 1,000 µg/mL Stock Standard |
| 80. µg/mL | 20 mL to 250 mL |
| 40. µg/mL | 20 mL to 500 mL |
| 5.0 µg/mL | 5 mL to 1,000 mL |
6.5. Sample Preparation
- 6.5.1. Rinse all glassware and crucibles with 10%
HNO3 and DI H2O.
Rinse all plasticware with DI H2O. Allow
labware to air dry before using.
6.5.2. MCE filters
Prepare filters (also wipe smear tabs) suspected of containing particulate fluoride as follows:
6.5.3. Chemically-treated backup pads
| Note: | The MCE filter should always be prepared and analyzed even if the industrial hygienist specifies only an HF analysis. See Section 7.3. for more details. |
Place each impregnated backup pad into a clean 100-mL polyethylene beaker and add 25 mL of DI H2O. Allow the pads to desorb for at least 1 h. Agitate each solution occasionally while desorbing.
6.6. Instrument Set-up
Follow the manufacturers' instructions or the SOP (8.5.) for
operation of the analytical instrument and electrodes. Use a
- 6.6.1. Connect the pH electrode (and reference electrode, if
necessary) to the millivolt/pH meter. Calibrate the instrument using
two buffers in the pH 4 to 10 range.
6.6.2. Individually adjust the pH of each sample to within 4.5 to 10.5 using an eyedropper or Pasteur pipet with dilute HCl or NaOH as needed.
| Note: | Do not use a large amount of solution to adjust the pH. A few drops should be sufficient. The desorbed solutions from the backup pads normally should not need any adjustment to achieve a pH within 4.5 to 10.5. |
Rinse the electrode after each standard or sample measurement.
6.6.3. While adjusting the pH of the samples, periodically check the instrument for drift by measuring the pH buffers.
6.6.4. Connect the fluoride ISE and reference electrode leads to the appropriate sites of the instrument, place the electrodes in a standard solution, and allow to stabilize.
6.7. Analytical Procedure
- 6.7.1. Prepare working standards immediately before analysis as
follows: Pipet 25 mL of the 80-, 40-, and
| Note: | The total microgram content of the three standards is 2,000, 1,000, and 125 µg, respectively. Other standards in this range may be used if desired. |
6.7.2. Quantitatively transfer samples from their volumetric
flasks into
6.7.3. Using the mV scale on the millivolt/pH meter, scan each sample and compare the mV reading to the standards. Always rinse the ISE with DI H2O and blot dry with a clean dry tissue before placing it in the next solution to be analyzed. If any mV reading is lower (less negative) than that of the highest standard, the sample is above the calibration curve and therefore must be diluted.
6.7.4. If a sample appears to be greater than the PEL, the sample may be split into two aliquots, which can be diluted and analyzed separately. To decide whether a sample should be split for duplicate analyses, estimate the concentration of the sample using data presented in the Appendix. For example, if the sample mV reading is near the 1,000 µg standard and the air volume of the sample is near 200 L, then the estimated air concentration is about 5 mg/m3.
| Note: | This calculation is only an estimate - it does not include blank corrections, Time Weighted Average calculations, etc. and is offered only as a convenience to allow for duplicate sample analyses. Final assessment of an overexposure is performed by the industrial hygienist. |
6.7.5. Sample dilutions
To estimate the approximate concentration of any samples above
the highest standard, apply the following rule: Doubling the
concentration of the analyte will change the initial mV reading
(Eo) by about 18 mV. Therefore, if the sample has an
initial mV reading 18 mV less than the initial mV reading of the
prepared standard, it is twice as concentrated as the standard.
Similarly, a sample reading 36 mV lower than the standard is four
times as concentrated. For samples that are 18 mV or less below the
highest standard, pipet a
| Note: | The 1:1 T-T buffer/DI H2O used
for |
6.7.6. Place the fluoride and reference electrodes into a
standard solution. Allow the reading to stabilize and record the
reading. Remove the electrodes from the standard solution, rinse
with DI H2O, and blot dry. Analyze a
different concentration standard (usually a ten- to
| Note: | The fluoride ISE can be affected by changes in temperature. Standards and samples should be at the same temperature before analyzing. Fluctuations in the ambient temperature during analysis can sometimes be compensated for by slope adjustment (see reference 8.4. for further details). |
6.7.7. If available, use a standard additions program intrinsic
within the instrument to calibrate and convert readings directly to
concentration values. If an automated program is not available,
record the mV reading prior to standard addition (Eo) and
after addition (Es). The "standard addition" is a
6.7.8. Analyze a sample or standard (Eo). Using a glass or automatic pipet, add a 1,000 µg (as F¯) spike, and then take a final reading (Es or concentration for automated programs). Follow the SOP for the particular instrument (8.5.) or manufacturers' guidelines. Analyze a standard in the concentration range of the samples after every fifth or sixth sample and at the end of the analysis.
7. Calculations
- 7.1. Determine the total g fluoride content of each sample and
blank using a
If mV readings were taken, plot the mV readings using an appropriate standard additions program. An example of equations used for standard additions can be found in reference 8.6. or in ISE manuals.
| Note: | Recall that 25 mL of dilute T-T buffer and 1 mL NaF spike is added to each standard and sample. Since this volume is constant for all samples and standards, the total µg content of each sample and standard can be calculated after standard addition computation as: | ||
| µg fluoride = µg/mL fluoride × Solution Volume × Dilution Factor | |||
| Where: | |||
| Solution Volume | = | Standard or sample volume (mL) without the addition of
| |
| Dilution Factor | = | Factor from Section 6.7.5. | |
7.2. Each air sample is blank corrected and the concentration is then calculated to determine particulate fluoride or hydrogen fluoride exposure using the following equations:
Particulate fluoride
| mg/m3 fluoride = | µg sample - µg blank
air volume, L |
Where:
µg Sample or Blank = From above calculation (Section 7.1.)
Hydrogen fluoride
| ppm HF = | MV × (µg sample - µg blank)
molecular weight × air volume, L |
Where:
| MV (Molar Volume) | = | 24.45 (25 °C and 760 mmHg) |
| µg Sample or Blank | = | From Section 7.1. |
| Molecular Weight (HF) | = | 20.006 |
| Gravimetric Factor | = | 1.05 |
7.3. Reporting Results
| Note: | Problems have occurred concerning the discrimination between
particulate and hydrogen fluoride (See references 8.3. and 8.7.
for further details). Past studies (8.3., 8.8.) have indicated
that HF did not significantly react with the MCE filter, styrene
cassette, or an untreated backup pad before collection on the
|
Results are reported to the industrial hygienist as follows:
For particulate fluoride (MCE filters), sample results are reported as mg/m3 fluoride.
For chemically-treated backup pad or MFGB samples, results are reported as ppm hydrogen fluoride.
8. References
- 8.1. Hawley, G.G.: The Condensed Chemical
Dictionary. 11th ed. New York: Van Nostrand Reinhold Co., 1987.
8.2. Occupational Safety and Health Administration Technical Center: OSHA Laboratory Quality Control Division Data by B. Babcock, Salt Lake City, UT. 1990 (unpublished).
8.3. Einfeld, W., and S.W. Horstman: Investigation of a dual
filter sampling method for gaseous and particulate fluoride. Amer.
Ind. Hyg. Assoc. J. 40:
8.4. Orion Research Incorporated: Instruction Manual,
Fluoride Electrodes, Model
8.5. Occupational Safety and Health Administration Technical Center: Ion Specific Electrode Standard Operating Procedure. Salt Lake City, UT. In progress (unpublished).
8.6. Occupational Safety and Health Administration Analytical
Laboratory: OSHA Manual of Analytical Methods edited by
R.G. Adler (Fluoride as F¯ and HF. Method No.
8.7. Lorberau, C., and K.J. Mulligan: Problem identified with NIOSH method 7902. Appl. Ind. Hyg. 3: 302 (1988).
8.8. Laboratory Services, Worker's Compensation Board of British Columbia: Hydrogen Fluoride in Air (Analytical Method No. 0751). Vancouver, B.C., Canada: Worker's Compensation Board of British Columbia, 1989.
Appendix
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| ||||||||||
| - - - - - - - - - - - - - - - - - - - Concn - - - - - - - - - - - - - - - - - - - - | ||||||||||
| 50 | 100 | 250 | 500 | 1,000 | 2,000 | µg | ||||
|
| ||||||||||
| Air Vol (L) | ||||||||||
| 50 | 1.0 | 2.0 | 5.0 | 10.0 | 20.0 | 40.0 | ||||
| 100 | 0.5 | 1.0 | 2.0 | 5.0 | 10.0 | 20.0 | ||||
| 150 | 0.67 | 1.67 | 3.33 | 6.67 | 13.3 | |||||
| 200 | 0.50 | 1.25 | 2.50 | 5.0 | 10.0 | |||||
| 250 | 1.0 | 2.0 | 4.0 | 8.0 | ||||||
| 300 | 0.83 | 1.7 | 3.3 | 6.7 | ||||||
| 350 | 0.71 | 1.4 | 2.9 | 5.7 | ||||||
| 400 | 0.62 | 1.2 | 2.5 | 5.0 | (mg/m3) | |||||
| 450 | 0.56 | 1.1 | 2.2 | 4.4 | ||||||
| 500 | 0.50 | 1.0 | 2.0 | 4.0 | ||||||
| 550 | 0.90 | 1.8 | 3.6 | |||||||
| 600 | 0.83 | 1.7 | 3.3 | |||||||
| 700 | 0.77 | 1.4 | 2.9 | |||||||
| 800 | 0.71 | 1.2 | 2.5 | |||||||
| 900 | 0.67 | 1.1 | 2.2 | |||||||
| 1000 | 0.62 | 1.0 | 2.0 | |||||||
| mg/m3 values are based on the equation: | ||||||||||
| ||||||||||
| µg | = | estimated reading obtained (as F¯) | ||||||||
| GF | = | gravimetric factor (1 for F¯, 1.05 for HF) | ||||||||
| PEL | = | 2.5 mg/m3 F¯ and 3 ppm HF | ||||||||
| Conversion of mg/m3 HF to ppm values can be accomplished by multiplying the mg/m3 HF value by 1.222. | ||||||||||