US Dept of Labor

Occupational Safety & Health AdministrationWe Can Help

Chlorine In Workplace Atmospheres

OSHA Method ID-101 | 1982, Revised May 1991

Search Sampling and Analytical Methods

For problems with accessibility in using figures and illustrations, please contact the Salt Lake Technical Center at 801-233-4900.
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.

The tables on this page are best viewed on a desktop, notebook, or tablet computer.

Method no.: ID-101
Matrix: Air
OSHA Permissible Exposure Limits: Final Rule Limits 1 ppm Chlorine (Short-Term Exposure Limit)
0.5 ppm Chlorine (Time Weighted Average)
Transitional Limit 1 ppm Chlorine (Ceiling)
Collection Device: A calibrated personal sampling pump is used to draw a known volume of air through a midget fritted glass bubbler containing a 0.1% sulfamic acid solution.
Recommended Sampling Rate: 1 L/min
Recommended Air Volumes
Short-Term Exposure Limit:
Time Weighted Average:

Analytical Procedure: An aliquot of the sulfamic acid solution is added to a buffered potassium iodide solution. Any chlorine contained in the first solution oxidizes the potassium iodide to iodine which is then measured with a residual chlorine ion specific electrode.
Detection Limit:

0.014 ppm (15-L air sample)
Quantitative 0.14 ppm (15-L air sample)
Precision and Accuracy:
Validation Level:

0.56 to 2 ppm (15-L air sample)
CVT 0.03
Bias -0.006
Overall Error ±6.6%
Classification: Validated Method
Chemists: Steven Edwards, James Ku


1982, Revised May 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 chlorine in the workplace. It is applicable for both Short-Term (STEL) and Time Weighted Average (TWA) exposure evaluations.

    1. History

      Chlorine was previously determined using o-tolidine (8.1). The previous OSHA sampling method for chlorine was to capture it in a dilute o-tolidine/hydrochloric acid solution and then analyze the sample using a colorimetric procedure. This method was used as a field test to immediately determine atmospheric chlorine concentrations. Due to problems associated with interferences, instability, and hazards associated with the collecting media, this method is no longer used by OSHA. Another method which utilized the ability of chlorine to bleach an acidic methyl-orange solution had been reported (8.2); however, without any modifications the method was too sensitive for concentrations pertinent to industrial hygiene applications. Sample instability and significant interferences were also noted.

      A method was developed by OSHA during the early 1980s which collected chlorine in a sulfamic acid solution and samples were analyzed using an ion specific electrode technique. The sulfamic acid collection and residual chlorine ion specific electrode (RCE) analysis has been evaluated (8.3) and has shown an acceptable level of precision and accuracy for the determination of chlorine in workplace atmospheres. Another evaluation by an independent laboratory has also been conducted (8.4).

    2. Principle

      The sampling method is based on a previous report of chlorine collection in sulfamic acid solutions (8.5). The analytical method is based on iodometric measurements of chlorine using a RCE. An iodide and a buffer reagent are added to the sulfamic acid-chlorine sample and the iodide reacts completely with the chlorine to form iodine:

      Cl2 + 2I- »   ----->  2Cl- + I2

      The iodine concentration formed after the reaction is indirectly measured by the RCE and is equal to the chlorine concentration before reaction. This reaction takes place in an acetic acid/sodium acetate buffer. This buffer provides the optimal pH range for the reaction (8.6).

    3. Advantages and Disadvantages
      1. This method has adequate sensitivity for measuring workplace concentrations of chlorine contained in the atmosphere.
      2. No sample elution or desorption is required because the sample is collected in a liquid medium.
      3. Collected samples are stable for at least 30 days before analysis.
      4. The analytical equipment is inexpensive.
      5. One disadvantage of this method is the use of a liquid in midget fritted glass bubblers (MFGB) to collect samples. Spillage or breakage can occur if precautions are not taken.
    4. Properties (8.2, 8.7)

      Chlorine (CAS No. 7782-50-5) is a greenish-yellow gas with an irritating odor. Some physical properties of chlorine are:

      Atomic Number 17
      Atomic Symbol Cl
      Molecular Weight (Cl2) 70.91
      Boiling Point -33.6°C
      Density 13.546 g/mL (20°C)
      Vapor Pressure 670.8 kPa (6.62 atm) at 20°C
      Color (gas) yellow-green
      Flammability nonflammable
      Solubility (H2O) 2.26 L of chlorine will dissolve in 1 L of H2O at 20°C

      Chlorine reacts readily with metals, and by substitution or addition with a wide variety of organic compounds.

    5. Uses

      Chlorine is used primarily as a bleaching agent or for chlorination of various organic compounds. Some industrial operations which have the potential for chlorine exposures are (8.2):

      Aerosol propellant makers Iron detinners
      Alkali salt makers Iron dezinkers
      Aluminum purifiers Laundry workers
      Benzene hexachloride makers Methyl chloride makers
      Bleachers Paper bleachers
      Bleaching powder makers Petroleum refinery workers
      Bromine makers Phosgene makers
      Broommakers Photographic workers
      Carpetmakers Pulp bleachers
      Chemical synthesizers Rayon makers
      Calcium chloride makers Refrigerant makers
      Chlorinated solvent makers Rubber makers
      Chlorinated hydrocarbon makers Sewage treaters
      Chlorine workers Silver extractors
      Colormakers Sodium hydroxide makers
      Disinfectant makers Submarine workers
      Dyemakers Sugar refiners
      Ethylene glycol makers Sulfur chloride makers
      Ethylene oxide makers Swimming pool maintenance workers
      Flour bleachers Tetraethyl lead makers
      Fluorocarbon makers Textile bleachers
      Gasoline additive workers Tin recovery workers
      Gold extractors Vinyl chloride makers
      Inkmakers Vinylidene chloride makers
      Insecticide makers Water treaters
      Iodine makers Zinc chloride makers

  2. Working Range and Detection Limits
    1. Using the iodide reagent as directed in the analytical procedure for chlorine, a linear response up to 20 µg/mL chlorine can be produced when the electrode potential versus log (Cl2) concentration is plotted (8.6). To bring large concentrations (>20 µg/mL) into the linear working range, these samples can be diluted with 0.1% sulfamic acid solution before any aliquots are reacted with the iodide/buffer reagents.
    2. Qualitative and quantitative detection limits of 0.01 and 0.1 µg/mL, were estimated during validation studies and calculates to 0.25 and 2.5 µg per sample, respectively.
  3. Method Performance (8.3)

    Validation studies conducted over the concentration range of 0.56 to 2 ppm (15-L air volume) gave an overall pooled coefficient of variation of 0.03, a bias of -0.006, and an overall error of ±±6.6%. Overall error was calculated using the equation:

    OEi   =   ± [ |mean biasi |   +   2CVi] × 100% where i is the respective sample pool being examined.

  4. Interferences

    Strong oxidizing agents including iodate, bromine, cupric ion, and manganese dioxide have been reported to interfere during analysis (8.6). These agents may react with the KI and produce a positive interference.

    It has also been reported that silver and mercuric ion concentrations above 10 to 20 µg/mL in the sampled solution will also interfere with the analysis (8.6) by poisoning the RCE. However, concentrations of this magnitude may be unlikely when sampling for chlorine in the workplace.

    Reduced sulfur-containing compounds (i.e., methyl mercaptan, dimethyl sulfide, dimethyl disulfide) and sulfur dioxide have been reported as negative interferences (8.4). These compounds apparently inhibit the recovery of chlorine from the sulfamic acid solution.

    Particulate (i.e., hypochlorites, trichloroisocyanuric acid) which may break down to free chlorine in the sulfamic acid solution are a positive interference. Particulate may be excluded from the sulfamic acid solution by using a Teflon prefilter during sampling.

  5. Sampling
    1. Equipment

      Note: If the workplace air being sampled is suspected of containing particulate (i.e., sodium hypochlorite, trichloroisocyanuric acid) which may liberate free chlorine in the collection solution, a prefilter as mentioned in Section 5.1.7 should be used.

      1. Collection solution, 0.1% sulfamic acid: Dissolve 1.0 g sulfamic acid in deionized water and dilute to the mark in a 1-L volumetric flask.
      2. Personal sampling pumps capable of sampling within ±5% of the recommended flow rate of 1 L/min are used.
      3. Midget fritted glass bubblers (MFGBs) (25-mL, part no. 7532, Ace Glass Co., Vineland, NJ).
      4. Shipping vials: Scintillation vials, 20-mL, part no. 74515 or 58515, (Kimble, Div. of Owens-Illinois Inc., Toledo, OH) with polypropylene or Teflon cap liners. Tin or other metal cap liners should not be used.
      5. A stopwatch and bubble tube or meter are used to calibrate pumps.
      6. Various lengths of PVC tubing are used to connect bubblers to the pumps.
      7. If any particulate may present an interference, a prefilter is attached to each bubbler such that sampled air enters the prefilter first. The prefilter should consist of:
        • a. Carbon-filled polypropylene cassette, 25-mm diameter, (part no. 300075, Nucleopore Corp., Pleasanton, CA).
          b. Filter for particulate collection, PTFE, 0.45 µm pore size, 25-mm diameter (part no. 130620, Nucleopore).
          c. Porous plastic support pad, (part no. 220600, Nucleopore).

        Assemble the prefilter such that sampled air enters the PTFE filter first and the plastic support pad faces the MFGB.

    2. Sampling Procedure
      1. Calibrate the sampling pump with a MFGB containing about 10 mL of 0.1% sulfamic acid solution in-line. Also calibrate with a prefilter if necessary.
      2. Place 10 to 15 mL of 0.1% sulfamic acid solution in an MFGB. Connect the MFGB (and prefilter if necessary) to a calibrated sampling pump. If a prefilter is necessary, use a minimum amount of tubing to connect the MFGB and prefilter together. Place the sampling device in the breathing zone of the employee.
      3. Sample at a flow rate of 1 L/min. For STEL determinations, a minimum sampling time of 15 min is recommended.
      4. For measurements of TWA exposures, sample up to 240 min. Take enough samples to cover the shift worked.
      5. Transfer the collection solution into a 20-mL glass scintillation vial. Rinse the bubbler with 2 to 3 mL of fresh sulfamic acid solution and transfer the rinsings into the sample vial. Place the Teflon-lined cap tightly on each vial and seal with vinyl or waterproof tape around the caps to prevent leakage during shipment. Attach an OSHA 21 seal lengthwise around each vial.
      6. Prepare a blank solution by taking 10 to 15 mL of the sulfamic acid solution not used for collection and transfer to a 20-mL glass vial. Seal the vial as mentioned in Section 5.2.5.
      7. If a prefilter was used, the filter can be submitted for analysis of available chlorine. Immediately after sampling, remove each filter from it's cassette and place in individual vials containing about 5 mL of fresh 0.1% sulfamic acid solution. Also prepare a blank filter/sulfamic acid solution and then seal all vials as mentioned in Section 5.2.5.
      8. Request chlorine analysis on the OSHA 91A form. If prefilters are submitted, request the filters are analyzed for total available chlorine using OSHA stopgap method ID-101-SG.
      9. Ship the samples to the laboratory using appropriate packing materials to prevent breakage.
  6. Analysis
    1. Safety Precautions
      1. Care must be exercised when handling glacial acetic acid. Gloves and face protection should be used. The area where the acid is diluted should be well ventilated (NOTE: Do not vent acetic acid into hoods designated for perchloric acid use). Inhalation of acetic acid vapors should be avoided. The glacial acetic acid should be added to the aqueous solution, thus avoiding any splattering which can occur when water is added to a concentrated acid. If any acid contacts the eyes, skin, or clothes, flush the area immediately with copious amounts of cold water and then seek medical attention.
      2. Care should be exercised when using laboratory glassware. Chipped pipettes, volumetric flasks, beakers, or any glassware with sharp edges exposed should not be used.
      3. Pipetting is always done using a pipetting bulb, never by mouth.
    2. Equipment
      1. Residual chlorine electrode (Model 97-70, Orion Research Inc., Cambridge, MA).
      2. Millivolt meter, capable of relative mV or concentration readings (Model EA 940 Expandable Ionanalyzer, Orion Research Inc.).
      3. Laboratory glassware including Class A volumetric flasks, pipettes, beakers, graduated cylinders, etc.
      4. Beakers, disposable plastic.
      5. Analytical balance (0.01 mg).
    3. Reagents - All reagents used should be reagent grade or better.
      1. Deionized water (DI H20).
      2. Sulfamic acid solution, 0.1%: Dissolve 1.0 g sulfamic acid (NH2SO3H) in DI H2O2 and dilute to 1 L.
      3. Potassium iodide (KI), 0.5 M: Dissolve 20.75 g KI in DI H2O and dilute to 250 mL. The solution should be prepared daily.
      4. Buffer reagent, 6.4 M acetic acid/1.8 M sodium acetate: Dissolve 37.1 g sodium acetate in 100 mL of DI H2O. Add 92 mL of glacial acetic acid and dilute the solution to 250 mL using DI H2O. This buffer is acidic, having a pH of about 4.7. Prepare monthly.
      5. Stock Solution: Dissolve 0.500 g potassium iodate in DI H2O and dilute to 500 mL in a volumetric flask. This solution is equivalent to 1,000 µg/mL chlorine. Prepare every 6 months.
    4. Standard Preparation
      1. Dilute the 1,000 µg/mL stock solution (prepared in Section 6.3.5) with 0.1% sulfamic acid using dilutions to make 100-, 10-, and 5.0-µg/mL standard solutions.
      2. Working standards are prepared by diluting aliquots of the 100-, 10-, and 5.0-µg/mL standard solutions to the analytical range of 0.2 to 20 µg/mL. A dilution scheme is shown below (also see note in Section 6.5.3):


        standard (µg/mL)

        Standard SolutionAliquot (mL)

        Standard SolutionConcentration (µg/mL)

        Final Volume (mL)





















        Prepare the working standards the same day the analysis is performed. Use the following procedure for preparation:

          1. An aliquot of the indicated standard solution (either 100-, 10-, or 5.0-µg/mL) is placed into a 50-mL volumetric flask.
          2. Add 0.5 mL buffer reagent to the volumetric flask.
          3. Add 0.5 mL KI to the volumetric flask and swirl to mix the reagents; allow the solution to react for at least 2 min before proceeding.
          4. Dilute the working standard to volume (50 mL) with 0.1% sulfamic acid solution. Mix thoroughly by inverting the flask several times. Store in a dark environment until the analysis is performed.

    5. Sample Preparation

      Note: If prefilters are submitted for analysis, they should be analyzed for total available chlorine using OSHA stopgap method ID-101-SG.

      1. Collected liquid samples are stable for at least 30 days. Special precautions are not necessary during storage. Analyze samples the same day they are prepared for analysis.
      2. Measure and record each sample volume received.
      3. Place an aliquot of each sample solution into a separate 50-mL volumetric flask. It is recommended to take the majority of the solution for those air samples having less than 60-L air volumes (i.e., STEL or ceiling samples). If necessary, a duplicate analysis can be conducted using the remaining aliquot; however, sensitivity may be significantly decreased.

      4. Note: A "dilution" effect has been noted in the literature (8.8) and may result in a net decrease of analyte formed after reaction with KI. This effect is apparently caused by differences in pH of the sample or µ. µs and samples should be matrix matched using 0.1% sulfamic acid. The volume of the aliquot taken may also alter the pH (for further information see Reference 8.8). A significant "dilution" effect was not noted when µs and samples were prepared and diluted with 0.1% sulfamic acid, and the aliquot volumes were kept below 15 mL (8.9).

      5. React each aliquot with KI and prepare for analysis using the following steps:
        1. Add 0.5 mL buffer reagent to the volumetric flask.
        2. Add 0.5 mL KI to the volumetric flask and swirl to mix; allow the solution to react for at least 2 min before proceeding.
        3. Dilute the sample to volume (50 mL) using 0.1% sulfamic acid solution. Mix thoroughly by inverting the flask several times. Store in a dark environment until the analysis is performed.
    6. Analytical Procedure
      1. Set up the millivolt meter according to the µ Operating Procedure (8.10) or manufacturers' guidelines.
      2. Place the electrode into a disposable plastic beaker containing 1.0-µg/mL solution. Allow the electrode to stabilize (approximately 3 min) and then record the mV reading. Remove the electrode from the standard solution, rinse with DI H2O, and blot dry. Place the electrode into a 10-µg/mL solution and record the mV reading. The difference between the 1.0- and 10-µg/mL should be approximately 29 mV.
      3. Analyze the standards and samples according to the SOP (8.10).
      4. Take a fresh aliquot from the volumetric flasks and prepare as mentioned in Section 6.4. each time a standard is analyzed. Using a relative reading of 0 mV for the 1 µg/mL and equipment mentioned in Section 6.2, typical standard readings and differences in mV values are shown below:

        Std, µg/mL

        mV Reading











        Note: For the 1 µg/mL standard, a relative mV setting of zero was used. Absolute readings may be different.

      5. Always rinse the residual chlorine electrode with DI H2O and blot dry with a clean dry tissue before placing it in the next solution to be analyzed.
      6. Analyze a standard in the concentration range of the samples after every fourth or fifth sample and at the end of the analysis. If a sample reading indicates the concentration is greater than the largest standard, dilute the unreacted sample to bring the concentration within the analytical range:
        • 1. take an aliquot from the remaining unreacted sample,
          2. dilute with sulfamic acid, and
          3. follow the procedure described in Section 6.5.4.

      Do not dilute any reacted samples into the analytical range.

  7. Calculations
    1. Determine the total µg/mL chlorine content of each sample and blank using a concentration-response regression curve if readings were measured in concentration units. If mV readings were taken, plot the log (concentration) versus the mV readings and determine µg/mL chlorine for each sample and blank.
    2. The total µg chlorine for each sample or blank is calculated as:
    3. µg Chlorine


      µg/mL Chlorine × (sample volume, mL) × 50 mL

      (aliquot taken, mL)

      µg/mL Chlorine   =   From curve (Section 7.1)

    4. Each sample is blank-corrected and the air concentration is calculated to determine chlorine exposure using the following equation:
    5. ppm Chlorine


      MV × (µg sample - µg blank)

      molecular weight × air volume, L

      MV (Molar Volume)   =   24.45 (25°C and 760 mmHg)
          Molecular Weight (Cl2)   =   70.91

    6. Reporting Results Results are reported to the industrial hygienist as ppm chlorine.
  8. References
    1. American Public Health Association, American Water Works Association, Water Pollution Control Federation: Standard Methods for the Examination of Water and Wastewater. 13th ed., Washington, D.C.: American Public Health Association, 1971.
    2. National Institute for Occupational Safety and Health: Criteria for a Recommended Standard - Occupational Exposure to Chlorine (DHEW/NIOSH Pub. No. 76-170). Cincinnati, OH: National Institute for Occupational Safety and Health, 1976.
    3. Occupational Safety and Health Administration Technical Center: Chlorine in Workplace Atmospheres - Backup Report (ID-101) by J. Ku. Salt Lake City, UT. Revised 1991.
    4. National Council of the Paper Industry for Air and Stream Improvement, Inc.: A Laboratory Evaluation of the Sulfamic Acid-Iodometric Method for Determining Chlorine in Pulp Bleaching Area Workplace Atmospheres (Special Report No. 82-02). New York: NCASI, March 1982.
    5. Takeuari, J. et al.: Measurement of Chlorine in the Atmosphere. Osen Kenkyu (Air Pollution Research) 9(2): 210 (1974).
    6. Orion Research, Inc.: Residual Chlorine Electrode, Model 9970 Instruction Manual. Cambridge, MA: Orion Research, Inc., 1976.
    7. Fassett, D.W., ed.: Patty's Industrial Hygiene and Toxicology. 2nd rev. ed., Vol. 2. New York: John Wiley and Sons, 1963.
    8. Rando, R.J., and Y.Y. Hammad: A Diffusive Sampler for Gaseous Chlorine Utilizing an Aqueous Sulfamic Acid Collection Medium and Specific Ion Electrode Analysis. Appl. Occup. Environ. Hyg. 5(10): 700-706 (1990).
    9. Occupational Safety and Health Administration Technical Center: Dilution Effect Study by J. Ku. Salt Lake City, UT. 1991 (unpublished).
    10. Occupational Safety and Health Administration Technical Center: Standard Operating Procedure - Ion Specific Electrodes. Salt Lake City, UT. In progress (unpublished).
Back to Top

Thank You for Visiting Our Website

You are exiting the Department of Labor's Web server.

The Department of Labor does not endorse, takes no responsibility for, and exercises no control over the linked organization or its views, or contents, nor does it vouch for the accuracy or accessibility of the information contained on the destination server. The Department of Labor also cannot authorize the use of copyrighted materials contained in linked Web sites. Users must request such authorization from the sponsor of the linked Web site. Thank you for visiting our site. Please click the button below to continue.