2-Aminoethanol (monoethanolamine, MEA; CAS 141-43-5) has a molar mass of 61.08 g/mol, a vapour pressure of approximately 0.4 mm Hg at 25 °C, and complete miscibility with water. The equilibrium headspace concentration over the pure liquid is approximately 526 ppm by volume, based on the ideal gas relation. This saturated concentration is more than two orders of magnitude above most occupational exposure limits, so the term “low volatility” should not be interpreted as low inhalation hazard when open handling, agitation, or thermal stress occurs. In gas-sweetening amine loops, metalworking fluid blending, and surfactant intermediate production, airborne MEA can be present as vapour, mechanically generated mist, or reclaimer emissions. The exposure benchmarks in the United States, the European Union, and China differ in numerical value, conversion basis, and short-term excursion policy, as summarised in Table 1.

Table 1: Principal occupational exposure benchmarks for monoethanolamine.

Does the US OEL Adequately Reflect the Vapour Pressure and Sensory Irritation Data?

Under 29 CFR 1910.1000 Table Z-1, the OSHA permissible exposure limit for ethanolamine is 3 ppm (6 mg/m³) as an 8-hour time-weighted average. The NIOSH recommended exposure limit is 3 ppm (8 mg/m³) with a 15-minute short-term exposure limit of 6 ppm (15 mg/m³) and an immediately dangerous to life or health value of 30 ppm. The difference between the OSHA mass value and the NIOSH mass value for the same 3 ppm limit is a conversion artefact. Using the molar mass of 61.08 g/mol at 25 °C and 101.325 kPa, 1 ppm equals 2.50 mg/m³, so 3 ppm equals 7.5 mg/m³. NIOSH rounds this to 8 mg/m³, while OSHA retains the older printed value of 6 mg/m³. The ppm value remains the principal compliance figure in the United States.

The 3 ppm threshold is far below the saturated headspace concentration of approximately 526 ppm at 25 °C. Achieving 3 ppm from a saturated source requires a dilution factor of approximately 175. In gas-sweetening units, closed-loop reboiler and pump operations often maintain 8-hour averages below 1 ppm, but maintenance activities such as filter changes, reclaimer sludge handling, and line breaking can produce transient excursions above the short-term limit. The NIOSH IDLH value of 30 ppm corresponds to roughly 75 mg/m³ and remains below the equilibrium vapour concentration of the pure liquid. This reinforces the need for ventilation and process isolation rather than reliance on low vapour pressure alone.

The European Union indicative occupational exposure limit for 2-aminoethanol is reported as 2.5 ppm (6.3 mg/m³) as an 8-hour TWA, with a short-term value of 5 ppm (12.6 mg/m³) in consolidated member-state guidance. This EU benchmark is lower than the US 8-hour value of 3 ppm and lower than China’s mass-based limit when converted to parts per million. The German DFG MAK of 2 ppm (5.1 mg/m³) is stricter than the EU indicative value and is frequently adopted by multinational chemical and gas-processing operators as an internal exposure control benchmark. The German MAK also carries an H skin absorption notation and a peak limitation category I(1), meaning that transient excursions above 2 ppm are more tightly restricted than under the US 15-minute short-term limit.

Because the EU system operates through indicative occupational exposure limit values and national implementing measures, compliance measurements must be generated with a method that meets the performance requirements of EN 482:2012. For MEA, this standard requires expanded uncertainty of no more than 50% at 0.1–0.5 times the limit value and no more than 30% at 0.5–2 times the limit value. Sorbent tube sampling with solvent extraction and gas chromatography is the usual approach. High humidity can reduce recovery of primary amines from silica gel media, so field blanks and humidity-controlled validation are required before any comparison against the EU or German limit is made.

China’s PC-TWA Framework and the Mass-Based OEL Under GBZ 2.1-2019

China’s GBZ 2.1-2019 assigns monoethanolamine a permissible concentration–time-weighted average of 8 mg/m³ and a permissible concentration–short-term exposure limit of 15 mg/m³. At 25 °C and 101.325 kPa, 1 ppm equals 2.50 mg/m³; therefore the Chinese PC-TWA of 8 mg/m³ corresponds to 3.2 ppm, and the PC-STEL of 15 mg/m³ corresponds to 6.0 ppm. This places the Chinese 8-hour value slightly above the US 3 ppm benchmark and well above the German MAK of 2 ppm. The Chinese short-term value is numerically equivalent to the US NIOSH and ACGIH short-term limit of 6 ppm.

The mass-based format of GBZ 2.1-2019 avoids the historical conversion discrepancy that appears in the US OSHA text. Compliance surveys in Chinese metalworking fluid blending, detergent synthesis, and gas-sweetening facilities typically use personal air samplers operated at flow rates of 0.05–0.2 L/min for full-shift samples. Because the Chinese PC-TWA is expressed only in mass concentration, laboratory analytical results do not require a separate ppm conversion before comparison. Short-term exposure is assessed with 15-minute samples compared directly against 15 mg/m³. In operations where aqueous MEA is sprayed or agitated, the Chinese limit applies to the total collected airborne mass, including both vapour and mist fractions, unless a specified particulate size fraction is given in the sampling method.

A practical field limitation in Chinese gas-sweetening and CO₂-capture facilities is the formation of MEA carbamate in the presence of carbon dioxide. This reaction can bias sorbent tube and filter recovery, particularly under high humidity. Method validation under actual process gas composition is necessary when using Chinese GBZ/T 300 series sampling procedures. Without such validation, a measured PC-TWA may underestimate the total amine burden because carbamate-bound MEA may not desorb quantitatively from some silica gel media. This limitation is not unique to the Chinese standard, but it is more visible there because the compliance value is mass-based and combines all airborne forms.

When Dermal Absorption From Aqueous MEA Solutions Overrides the Airborne Limit

Because MEA is fully miscible with water and is a tissue-corrosive primary amine, direct skin contact with concentrated aqueous solutions can produce systemic uptake that is not reflected by an inhalation exposure limit. The German H notation and the Chinese percutaneous notation, where applied, recognise that the airborne OEL alone is insufficient for dermal risk assessment. In drum emptying, line breaking, and immersion cleaning using 5–30 wt% aqueous MEA, splashes to the forearms and hands can occur at vapour concentrations below the OEL. The airborne limit then gives no valid indication of the physiological dose.

Common disposable nitrile gloves have finite breakthrough times with primary amines and may provide only short-duration protection against concentrated MEA. Laminated barrier films or butyl rubber are specified for repeated contact. The pH of dilute aqueous MEA is strongly alkaline and supports the corrosive skin risk. In European Union operations, the inhalation OEL must therefore be paired with task-specific dermal risk management under the REACH registration dossier and national chemical safety guidance. In the United States and China, comparable requirements for chemical protective clothing and skin notation awareness are embedded in occupational health enforcement practice.

Airborne MEA is commonly collected on silica gel sorbent tubes, desorbed with methanol or dilute acid, and analysed by gas chromatography with flame ionisation, nitrogen-phosphorus, or mass-selective detection. NIOSH Method 3509 for ethanolamines and OSHA validated sorbent tube procedures are recognised United States methods. For a 3 ppm 8-hour concentration at 25 °C, a 10 L air sample is expected to contain approximately 75 µg of MEA using the 7.5 mg/m³ conversion. At the German MAK of 2 ppm, the expected collected mass is approximately 50 µg. Sorbent tube capacity is in the milligram range, so capacity breakthrough is less likely than recovery loss from humidity or acid-gas interference. High-CO₂ backgrounds can convert MEA to the carbamate on the sampling medium, producing low results unless the analytical method includes an acid-gas scrubber or derivatisation step. Without measurement quality control under EN 482:2012 or laboratory accreditation according to ISO/IEC 17025:2017, any comparison of national OEL values is incomplete because analytical uncertainty alone can exceed the numerical difference between the US, EU, and Chinese benchmarks.