Ethylene oxide sampling methods

The method specifies collecting air samples on two activated charcoal tubes in series and desorbing them with 1% carbon disulfide (CS2) in benzene. This is stated in the method description in 1910.1047 App D. Note that the appendix also warns that the use of benzene increases hazards in the lab (see the method disadvantages in 1910.1047 App D).

OSHA recommends collecting a 1.0‑liter air sample at a maximum sampling rate of 0.05 liters per minute (Lpm). These recommended values are given in the method summary and the Sampling Procedure in 1910.1047 App D. Employers should use a pump calibrated to achieve this flow within ±5% (see the apparatus requirements).

Samples must be analyzed within 15 days of the sampling date, because the method demonstrated sample stability for at least 15 days under routine conditions. This requirement and the 15‑day storage stability are specified in 1910.1047 App D.

Two tubes in series are required to detect possible breakthrough or migration of ethylene oxide from the primary tube to the backup tube. The appendix explains that breakthrough and migration can occur and therefore two tubes are used so the backup tube can show whether the front tube became saturated or ethylene oxide migrated downstream (see 1910.1047 App D).

The personal sampling pump must be calibrated so its flow can be determined within ±5% of the recommended flow. This pump accuracy requirement appears in the apparatus section of 1910.1047 App D.

The OSHA method specifies SKC Lot 120 charcoal tubes: glass tubes 7 cm long, 6 mm outside diameter, 4 mm inside diameter, with two sections of coconut shell charcoal separated by urethane foam (100 mg adsorbing section, 50 mg backup). These tube specifications are listed under Apparatus in 1910.1047 App D.

Place the two tubes in series with the tube nearer the pump used as the backup, keep the tubes vertical during sampling, and use a minimum length of flexible tubing so sampled air enters the front of the first tube directly. These sampling technique steps are described in the Sampling Procedure in 1910.1047 App D.

With each batch of samples, submit at least one blank tube from the same lot and subject it to the same handling (break, seal, transport) except no air is drawn through it; seal sampled tubes immediately after sampling with plastic caps and OSHA seals lengthwise. These procedures are specified in the Sampling Procedure in 1910.1047 App D.

The appendix reports a 5% breakthrough volume of about 2.6 liters (sampled at 0.05 Lpm) for a 3.0 mg/m3 ethylene oxide stream at roughly 85% relative humidity and 22 °C. To minimize breakthrough, employers can use larger capacity charcoal tubes, reduce the sampling flow rate, or shorten sampling time. Both the breakthrough data and these mitigation suggestions are discussed in 1910.1047 App D.

Based on a 1.0‑liter air sample, the method reports an overall detection limit of 13.3 parts per billion (ppb, 0.024 mg/m3) and a reliable quantitation limit of 52.2 ppb (0.094 mg/m3). These analytical performance numbers are provided in the method summary in 1910.1047 App D.

The average desorption efficiency reported for the OSHA-tested lot was 88% over 0.5 to 2× the target concentration, but desorption efficiency can vary by laboratory and by charcoal lot, so employers must determine the desorption efficiency for the specific lot used in their workplace. This requirement and the 88% average are discussed in 1910.1047 App D.

Wear safety glasses when breaking the tube ends, attach sampling equipment so it does not interfere with work, and, if possible, place tubes in a holder so the freshly broken sharp end is not exposed during sampling. These safety precautions are listed in the Sampling Procedure section of 1910.1047 App D.

The analytical method calls for gas chromatography with a linearized electron capture detector (ECD) and a GC column capable of separating the derivative (2‑bromoethanol) from interferences and the 1% CS2 in benzene solvent. These analytical requirements are stated in the Analytical Method section of 1910.1047 App D.

Yes. Inclusion of this method in the appendix does not mean it is the only satisfactory method; OSHA notes other validated methods (e.g., Union Carbide, Dow, 3M, DuPont, NIOSH Method S‑286) are available, but the employer must ensure the chosen method's accuracy and precision under their workplace conditions. This flexibility and the list of other methods are described in 1910.1047 App D.

Transport charcoal tube samples with their paperwork to the analyzing lab, sealing tubes after sampling; bulk liquid samples should be transported in glass containers with Teflon‑lined caps and shipped separately from the charcoal tubes. These handling and transport instructions appear in the Sampling Procedure in 1910.1047 App D.

Ethylene glycol and Freon 12 did not interfere at target concentration levels, but relative humidity may affect sampling (for example, water may displace ethylene oxide and contribute to breakthrough). The method asks that suspected interferences and conditions be noted on the sample data sheets; see the Interferences section of 1910.1047 App D.

Key disadvantages include the need for two tubes in series because of possible breakthrough and migration; limited sampling precision due to pressure drop across two tubes; increased lab hazard from benzene as the desorbing solvent; buildup of residue on the ECD over repeated injections that can reduce sensitivity; and nonlinear recovery at low concentrations. These method limitations are listed in the Disadvantages section of 1910.1047 App D.

Break the ends of the charcoal tubes immediately before sampling, and use tubes from the same lot because desorption efficiency and sampling characteristics can vary between lots of charcoal; lot consistency helps ensure comparable performance. These instructions are in the Sampling Procedure and Apparatus sections of 1910.1047 App D.

The method targets 1.0 ppm (1.8 mg/m3) and was developed because earlier methods had detection limits around 1 ppm and OSHA needed a method sensitive enough to measure much lower concentrations of ethylene oxide. The method target and its low‑level development motivation are described in 1910.1047 App D.

If employers observe breakthrough with the OSHA or other charcoal methods, they should try larger capacity charcoal tubes, reduce the sampling flow rate, or shorten the sampling time; and always verify any chosen method's accuracy and precision under their workplace conditions. These troubleshooting suggestions and the need to validate the method for unique workplace conditions are given in 1910.1047 App D.

The recommended sampling media is activated charcoal in a two-section (front and backup) charcoal tube, with the front and back sections treated and analyzed separately. The Appendix specifies transferring the front and back sections of each sample into separate 2‑mL vials for desorption and analysis (1910.1047AppD).

• Handle front and backup sections separately to detect breakthrough and for calculation (add analytical results from both tubes for the sample).

You should desorb each charcoal section with 1.0 mL of the desorbing reagent (99% benzene / 1% carbon disulfide). The procedure in the Appendix instructs using 1.0 mL per vial, sealing the vial immediately, and allowing desorption for one hour with occasional shaking (1910.1047AppD).

• After desorption, draw off the solvent with a disposable pipet into a clean 2‑mL vial before analysis.

You must use reagent‑grade benzene and carbon disulfide, pure ethylene oxide for standards, hydrobromic acid (48%), and anhydrous sodium carbonate; handle them in a chemical hood and avoid skin contact because benzene and ethylene oxide are carcinogens and HBr is highly toxic (1910.1047AppD).

• Perform all solvent work in a hood, wear eye protection, and avoid skin contact with solvents and HBr as described in the Appendix.

Standards are prepared by injecting pure ethylene oxide gas into the desorbing reagent; a concentration of 1.0 µL of ethylene oxide gas per 1 mL desorbing reagent equals 1.0 ppm air concentration for the recommended 1‑liter air sample at 25 °C and 760 mm (uncorrected for desorption efficiency) (1910.1047AppD).

• Remember to correct reported results for desorption efficiency using the desorption curve before reporting final air concentrations.

The recommended GC settings are nitrogen carrier flow 10 mL/min, injector 250 °C, detector 300 °C, column 100 °C, and an injection size of 0.8 µL with an elution time of about 3.9 minutes (1910.1047AppD).

• Peak areas should be measured with an integrator or other suitable means and used to construct a calibration curve (concentration vs. area).

Samples over the 1.0 ppm target level should be confirmed by gas chromatography/mass spectrometry (GC/MS) or another suitable confirmatory method. The Appendix specifically requires confirmation of elevated results to rule out interferences (1910.1047AppD).

• Confirmation helps identify possible co-eluting compounds that could falsely elevate the measured signal.

Any compound that has the same retention time as 2‑bromoethanol is a potential interference in this method. The Appendix warns that 2‑bromoethanol coelution can compromise specificity (1910.1047AppD).

• Use confirmation (GC/MS) for samples above the target or when interferences are suspected.

Analytical results must be corrected using a desorption efficiency curve derived from spiked recovery data; the Appendix describes computing a correction factor from the desorption curve and applying it to the measured analyte amount before calculating air concentration (1910.1047AppD).

• The Appendix provides recovery data at multiple spiked amounts showing recoveries ranging from about 74.5% to 96%, and notes nonlinearity at low amounts—use the provided desorption curve for accurate corrections.

You add the analytical results (A) from the two tubes that compose a particular air sample to obtain the total analyte amount for that sample before further calculation. The Appendix explicitly directs combining the results from the front and back sections (1910.1047AppD).

• After summing the corrected amounts from both tubes, proceed to calculate concentration using the desorption volume and sampled air volume as described in the Appendix.

You calculate sample concentration using the Appendix equation that combines the corrected analyte (A), desorption volume (B, mL), and air volume (C, L); then convert mg/m3 to ppm with the relationship ppm = (mg/m3 × 24.45) / 44.05 where 24.45 is the molar volume at 25 °C and 760 mm and 44.05 is the molecular weight of ethylene oxide (1910.1047AppD).

• Follow the Appendix equation (A × B ÷ C with appropriate unit conversions) and then use the provided constants 24.45 and 44.05 to convert mg/m3 to ppm.

The analytical detection limit is 1.20 × 10−5 µg per injection, which is equivalent to about 8.3 parts per billion (0.015 mg/m3) for the recommended air volume (1910.1047AppD).

• This detection limit was determined by injecting 0.8 µL of a 0.015 µg/mL standard into 1% CS2 in benzene.

Standards are prepared by injecting measured volumes of pure ethylene oxide gas into the desorbing reagent; prepare a range of standards to build a calibration curve and add one drop of HBr per mL and about 0.15 g sodium carbonate per drop as in sample preparation (1910.1047AppD).

• The Appendix gives the equivalence that 1.0 µL ethylene oxide gas per 1 mL desorbing reagent ≈ 1.0 ppm for a 1‑L sample (uncorrected for desorption efficiency).

Desorption recovery becomes non‑linear and declines at lower spike amounts; the Appendix data show percent recoveries falling to about 74.5% at the lowest spikes and note nonlinearity below certain amounts (1910.1047AppD).

• Because of this, use the desorption curve derived from multiple spike levels to correct low‑level results rather than a single average recovery.

Refrigerated storage (about 5 °C) preserves ethylene oxide samples better than ambient storage, and sample recoveries decline over time—Appendix storage data showed refrigerated samples generally retaining higher percent recovery than ambient samples over 19 days (1910.1047AppD).

• The Appendix shows variable recoveries over days; when using other methods the ASTM‑proposed procedure recommends shipment on dry ice and storage below −5 °C with analysis within three weeks to limit migration and sample loss.

The 5% breakthrough occurred when approximately 2.6 liters of test atmosphere were drawn through the charcoal tubes under the specified test conditions (2 ppm, ~85% RH, 22 °C) according to the Appendix breakthrough study (1910.1047AppD).

• Breakthrough data show rapid increase in backup tube percent breakthrough after a few tens of minutes at the study flow rate (0.050 L/min); using two sections in series is essential to detect and compensate for breakthrough.

Passive monitors (diffusive badges) may be appropriate for measuring time‑weighted average exposures when validated and when they meet precision and accuracy requirements; the Appendix discusses commercial passive dosimeters such as DuPont Pro‑Tek and 3M 350 that had validation data down to 0.2 ppm (1910.1047AppD).

• Choose passive monitors with demonstrated performance for your exposure range, understand their limits, and confirm elevated results by a validated method when required.

Detector tubes and direct‑reading instruments are useful for quick, on‑the‑spot screening and leak localization, but detector tubes are nonspecific and often lack accuracy while direct‑reading instruments vary in sensitivity and selectivity by technology (1910.1047AppD).

• Detector tubes: inexpensive and immediate but nonspecific—good for short‑term leak checks.
• Direct‑reading (IR, PID, portable GC): immediate and continuous; good for locating high pockets and leak detection but choose models with adequate sensitivity and known interferences.

You must work in a chemical hood, wear safety glasses, avoid skin contact with solvents and HBr, and treat ethylene oxide and benzene as potential carcinogens—take all listed precautions in the Appendix (1910.1047AppD).

• Use appropriate PPE (gloves resistant to carbon disulfide/benzene), fume hoods for solvent handling, and safe procedures for adding HBr and sodium carbonate due to the exothermic reaction.

Add one drop of hydrobromic acid per mL of desorbing reagent, mix, then add about 0.15 g sodium carbonate per drop of HBr; this neutralization step is part of the method to stabilize the analyte prior to analysis as described in the Appendix (1910.1047AppD).

• Add sodium carbonate carefully (small reaction will occur) and reseal vials after each addition to prevent losses and exposure.

You should validate linearity and precision by preparing multiple injections across the calibration range and computing slope, standard deviation, and coefficient of variation (CV) as the Appendix demonstrates; the method sensitivity and precision data (slope = 34.105 and CV values) provide benchmarks for method performance (1910.1047AppD).

• Run replicate injections at low, mid, and high calibration points and compare CV and slope to the Appendix data to ensure comparable performance.

If the backup tube shows significant ethylene oxide, the sample likely experienced breakthrough and the measured front‑tube value alone underestimates exposure; the Appendix requires adding both tube results and using breakthrough data to evaluate sampling adequacy (1910.1047AppD).

• Consider reducing sampled air volume, using different sorbent, or using a higher‑capacity tube or shorter sampling interval for future sampling to prevent breakthrough.

The Appendix recommends an injection size of 0.8 µL with an expected elution time of about 3.9 minutes under the specified GC conditions (1910.1047AppD).

• Use an integrator to measure peak areas and build your calibration curve from standards analyzed under the same conditions.

Yes. OSHA notes that many GC/PID units have sensitivity in the 0.1–0.2 ppm EtO range, which is adequate to detect concentrations around typical occupational monitoring levels.

• The appendix explains that GC/PID retains photoionization sensitivity while minimizing interferences and that several units reach about 0.1–0.2 ppm sensitivity (1910.1047AppD).
• Remember that meeting sensitivity is not the only requirement: employers must ensure monitoring methods meet the accuracy and precision expectations in the EtO standard itself (1910.1047).
• Practical tip: verify instrument calibration, use trained operators, and confirm method performance with known standards before using results for compliance decisions.

Yes. OSHA describes GC/PID units with microprocessors that can sequentially sample many points, record results, and activate alarms or ventilation systems when configured appropriately.

• The appendix says microprocessor-based GC/PIDs can sample up to 20 sample points sequentially, calculate and record data, and activate alarms or ventilation systems (1910.1047AppD).
• Ensure any multi-point configuration still meets the monitoring method’s accuracy and calibration requirements set out in the EtO standard (1910.1047).
• Practical steps: document sampling locations, verify response time for alarms, perform routine calibration checks at each sample location, and train staff on alarm response procedures.

OSHA and commenters discussed accuracy of ±25% at 1 ppm and ±35% below 1 ppm, and DuPont reported that its Pro-Tek badge met those criteria in their tests.

• The appendix quotes DuPont testimony saying the proposed accuracy standard of ±25% at one part per million and ±35% below that is appropriate, and DuPont’s data indicated that the Du Pont Pro-Tek badge was the only thoroughly tested method that met the accuracy requirement (1910.1047AppD).
• OSHA also noted that independent laboratory confirmation using the same dynamic chamber testing protocol was not submitted, and that other submitted data suggested some other methods could show equal or better precision and accuracy.
• Practical implication: when selecting a monitoring method for compliance, employers should look for documented accuracy relative to these benchmarks and prefer methods validated by independent laboratories or accredited testing.

The skill and experience of sample collectors and analytical laboratories significantly affect EtO monitoring accuracy, and employers should choose experienced, accredited labs and well-trained samplers.

• OSHA explicitly states that the accuracy of any method depends greatly on the skills and experience of those who collect and analyze the samples, and that some laboratories are closer to true values than others (1910.1047AppD).
• Actions employers should take: use labs with appropriate accreditation or proficiency testing, require method-specific quality control (calibration curves, blanks, spikes), document sampler training and chain-of-custody, and, if practical, send split or blind samples to a second lab to check consistency.
• Also ensure monitoring plans meet the procedural and frequency requirements in the EtO standard (1910.1047).

No; a PID reduces many interferences but does not always completely eliminate them, so confirmatory steps and good method design are still needed.

• OSHA notes that a GC/PID "retains the photionization sensitivity, but minimizes or eliminates interferences," indicating reduced but not guaranteed elimination of all interferences (1910.1047AppD).
• Because other volatile organic compounds can sometimes respond on a PID, employers should use chromatographic separation (the GC part), appropriate sampling media, and method-specific calibration to distinguish EtO from other compounds.
• Practical measures: perform background surveys, run interference checks with likely co-contaminants, and use laboratory confirmation when results are near action levels in the EtO standard (1910.1047).

An employer should seek independent validation, verify method performance in their workplace, and document quality control before relying on that method for compliance.

• OSHA observed that DuPont’s claim that only the Pro‑Tek badge met accuracy requirements was not accompanied by independent laboratory confirmation using the same dynamic chamber protocol, and that independent data are important for confirming performance (1910.1047AppD).
• Recommended steps: obtain independent or third‑party laboratory validation of the method, run side‑by‑side tests (split samples) in your facility, verify method accuracy and precision meet the ±25% at 1 ppm and ±35% below 1 ppm benchmarks discussed in the appendix, and keep records of validations and QC checks to demonstrate due diligence under the EtO standard (1910.1047).
• If independent validation is not feasible, use conservative approaches (e.g., more frequent sampling, multiple methods, or laboratory confirmation) until sufficient evidence of method performance exists.