1.1.1. Nomenclature

• Chem. Abstr. Serv. Reg. No.: 116-14-3
• Chem. Abstr. Serv. Name: Tetrafluoroethylene
• IUPAC Systematic Name: 1,1,2,2-Tetrafluoroethene
• Synonyms: Perfluoroethylene, Perfluoroethene, Ethylene tetrafluoro-, tetrafluoroethene

1.1.2. Structural and molecular formulae, and relative molecular mass

• 
• Molecular formula: C₂F₄
• Relative molecular mass: 100.01

1.1.3. Chemical and physical properties of the pure substance

• From IFA (2014), unless otherwise indicated
• Description: Colourless gas, odourless or sometimes described as having a faint sweetish odour; extremely flammable
• Boiling point: −75.63 °C
• Melting point: −131.15 °C (HSDB, 2014)
• Density: 4216 kg/m³ at 15 °C at 1 bar
• Solubility: Slightly soluble in water, 159 mg/L at 25 °C (HSDB, 2014)
• Vapour pressure: 2947 kPa and 20 °C
• Stability: Decomposes into fluorine and fluorine compounds when heated (HSDB, 2014)
• Reactivity: A terpene inhibitor (limonene) is generally added to the monomer to prevent spontaneous polymerization.

Risk of explosion in contact with air or in the absence of air at elevated temperatures and/or pressures (> 600 °C and 100 kPa). The stabilized monomer is flammable in air if ignited (flammability limits: lower, 11%; upper, 60%) producing soot and carbon tetrafluoride (Babenko et al., 1993; HSDB, 2014).

Incompatible with polymerization catalysts and peroxides. May react exothermically with chloroperoxytrifluoromethane, sulfur trioxide and several other substances (HSDB, 2014). May react if in contact with aluminium, copper and their alloys, resulting in an uncontrolled exothermic reaction (ECHA, 2014).

Octanol/water partition coefficient (P): log P = 1.21 (estimated) (HSDB, 2014)

Conversion factor: Assuming normal temperature (25 °C) and pressure (101 kPa), 1 mg/m³ = 4.09 ppm, calculated from mg/m³ = (relative molecular mass/24.45) × ppm.

1.1.4. Technical products and impurities

Industrial-grade tetrafluoroethylene generally has a purity of > 99.7%. Impurities may include various chloro-fluoro compounds (ECETOC, 2003). Limonene may be added to prevent spontaneous polymerization (HSDB, 2014).

1.1.5. Analysis

A range of sampling and analytical methods can be used to measure exposure to tetrafluoroethylene, although there is only one validated method from the United States National Institute of Occupational Safety and Health (NIOSH), based on using a Fourier transform infra-red (FTIR) spectrometer to directly detect tetrafluoroethylene. Selected available methods are summarized in Table 1.1.

Table 1.1

Methods for the analysis of tetrafluoroethylene.

Generic methods for the collection of volatile organic substances using solid sorbents such as activated charcoal, followed by analysis using gas chromatography (GC) have been used to measure occupational exposure. It is also possible to sample air contaminated with tetrafluoroethylene into a solid stainless steel container, and to then analyse the sample using gas chromatography-mass spectrometry (GC-MS).

1.2.1. Production process

1.2.2. Uses

Tetrafluoroethylene is used in the manufacture of oligomers, fluoroelastomers and fluoropolymers. The main use of tetrafluoroethylene is in the manufacture of polytetrafluoroethylene that is used as nonstick coatings on cookware, membranes for clothing that are both waterproof and breathable, electrical-wire casing, fire- and chemical-resistant tubing, and plumbing thread seal tape. It reacts with perfluoronitrosoalkanes to produce nitroso rubbers. It is also used in the production of compounds and intermediates of low relative molecular mass, including for the manufacture of iodoperfluoroalkanes (NTP, 2014).

1.3.1. Environmental occurrence

1.3.2. Occupational exposure

Occupational exposure occurs in the primary manufacture of tetrafluoroethylene and during the subsequent polymerization process.

Inhalation exposure has been measured in several European plants manufacturing tetrafluoroethylene. ECETOC (2003) reported levels of between 0.16 and 6 mg/m³ in one plant, and between < 0.4 and 6.1 mg/m³ (95% of samples, < 2 mg/m³) in a second plant, in both data sets as an 8-hour time-weighted average. No other published data were available for workplace exposures to tetrafluoroethylene.

As part of an international epidemiological study of workers in six plants manufacturing polytetrafluoroethylene in Germany, the Netherlands, Italy, the United Kingdom, and the USA (New Jersey and West Virginia), Sleeuwenhoek & Cherrie (2012) made estimates of exposure to tetrafluoroethylene by inhalation using modelling methodology. The exposure reconstructions were made using descriptive information about the workplace environment and work processes, including changes over time. The methodology allowed for key changes in exposure modifiers such as local ventilation, use of respiratory protective equipment, working in a confined space, outdoor work, cleanliness, and the level of involvement of the workers in the process (e.g. operator or supervisor). There were very few measurements of exposure available from the plants (all unpublished), and so the exposure estimates were expressed on an arbitrary dimensionless scale. Two assessors made assessments independently and the results were then combined (Sleeuwenhoek & Cherrie, 2012).

In each plant, the highest estimated exposures for tetrafluoroethylene occurred in the polymerization area. The introduction of control measures, increasing process automation and other improvements, were judged to have resulted in exposures generally decreasing over time. In the polymerization area, the annual estimated decline in exposure to tetrafluoroethylene varied by plant from 3.8% to 5.7% (see Fig 1.1). The differences in the estimated exposure level for polymerization workers at any time were up to about fivefold. Part of these inter-plant differences can be explained by differences in technology and the work responsibilities of operators (Sleeuwenhoek & Cherrie, 2012). The biggest changes in exposure for polymerization workers were mainly due to the introduction of automatic cleaning and automation at the autoclaves. Other improvements causing important declines in exposure levels were the introduction of localized ventilation and vacuum extraction at the end of the polymerization process (Sleeuwenhoek & Cherrie, 2012).

Fig. 1.1

Change in levels of exposure to tetrafluoroethylene for operators working in polymerization areas of six plants manufacturing polytetrafluoroethylene

Operators in the monomer area always wore breathing apparatus when undertaking tasks where exposure to tetrafluoroethylene was possible, and so inhalation exposure for these workers would have been very low. In this area of the plants there were small decreases in estimated exposure levels due to general environmental improvements, such as the use of more efficient pumps and gaskets (Sleeuwenhoek & Cherrie, 2012).

Tetrafluoroethylene exposure for workers in the finishing areas of the plants was consistently low over the history of the plant. The decline in exposure levels was generally smaller in finishing areas than in other areas, and the changes were primarily due to improved general ventilation (Sleeuwenhoek & Cherrie, 2012).

Historically, workers in polytetrafluoroethylene production were potentially exposed to both tetrafluoroethylene and the ammonium salt of perfluorooctanoic acid (PFOA), which is also the subject of a Monograph in the present volume). Only a small number of jobs with lower exposure to tetrafluoroethylene had no possible exposure to ammonium perfluorooctanoate. Workers in most jobs were exposed to both chemicals, and there was a strong positive correlation between estimated exposure to tetrafluoroethylene and ammonium perfluorooctanoate (r = 0.72, P < 0.001) (Sleeuwenhoek & Cherrie, 2012).

[The Working Group considered that the limited quantity of data on measured occupational exposure suggested that in about 2000 the highest tetrafluoroethylene exposure levels in manufacturing plants were about 6 mg/m³, and considering the temporal trends described above (average change over the history of production, about sixfold), it seems probable that the highest occupational average exposures to tetrafluoroethylene in the polytetrafluoroethylene-manufacturing industry in the 1950s and 1960s would have been < 40 mg/m³.]

1.3.3. Exposure of the general population

No information was available about the levels of exposure to tetrafluoroethylene in the general population, although because of the necessity to contain the substance within an enclosed system due to its flammable nature, it is likely that any exposure is very low and localized around industrial facilities manufacturing or using tetrafluoroethylene. Tetrafluoroethylene is not detectable in its polymerized products, including polytetrafluoroethylene (analytical detection limit, < 0.05–0.01 mg/kg) (ECETOC, 2003). When heated to temperatures above those normally used for cooking, polytetrafluoroethylene-coated pans may emit tetrafluoroethylene, although the major hazard in such circumstances is particulate fumes, which can cause serious acute effects (NIOSH, 1977).