8 Glossary and definition of terms
Certain terms used within this document have specific meanings and these meanings have certain implications. Furthermore the terms ‘dangerous fluid’ and ‘dangerous substance’ have specific legislative impact. In addition the terminology of carbon dioxide phases is explained.
The term ‘dangerous substance’ is a term applied to substances as classified under the Dangerous Substances Directive (67/548/EEC)123. A substance that is considered a ‘dangerous substance’ falls into any of the following classes:
- oxidising agents;
- flammable substances or preparations;
- toxic substances or preparations;
- harmful substances or preparations;
- corrosive substances or preparations;
- sensitisers ;
- substances or preparations that are toxic for reproduction, and
- substances or preparations that are dangerous for the environment.
General classification of carbon dioxide is that it is excluded from the list of toxic substances with exposure limits of 5 000 ppm time weighted average (TWA) and 30 000 ppm short term exposure limit (STEL) and is not listed as a dangerous substance under the directive. However carbon dioxide does have a known toxicity and is considered an asphyxiant but at high concentrations. There are two key definitions: the United Nations publishes model regulations124 that classify substances that are transported, and this is the accepted classification that appears on material safety data sheets; the other is the UK Chemicals (Hazard Information and Packaging for Supply) (CHIP) Regulations125 and supporting directive126. The definition of Toxic from the Chemicals (Hazard Information and Packaging for Supply) Regulations 2009127 is:
“Substances and preparations which in low quantities cause death or acute or chronic damage to health when inhaled, swallowed or absorbed via the skin.”
and the definition of toxic and non-toxic under the UN Recommendations on the Transport of Dangerous Goods Model Regulations128 is:
Division 2.3 Toxic gases
- are known to be so toxic or corrosive to humans as to pose a hazard to health; or
- are presumed to be toxic or corrosive to humans because they have an LC50 value (as defined in section 18.104.22.168) equal to or less than 5 000 ml/m3 (ppmv).
The UN classification of carbon dioxide is Division 2.2 - non-toxic gas and given the Chemicals (Hazard Information and Packaging for Supply) Regulations definition, carbon dioxide would not qualify as toxic. The United Nations has set out to harmonise such definitions internationally. The Globally harmonized system of classification and labelling of chemicals (2007) discusses the definition of ‘toxic’ material in Part 3: Health Hazards; this standard methodology of classification, like the transportation and CHIP regulations would indicate that carbon dioxide is not toxic.
The LC50 value for carbon dioxide is considered by the US National Institute of Occupational Safety and Health (NIOSH) to be 40 000 ppm129, although some studies130 indicate the value may be 100 000 ppm, far above the threshold required for the UN classification of toxic.
In the UK the HSE has stated131 that carbon dioxide is to be considered a dangerous substance when considering carbon capture and storage schemes. This instruction automatically applies the requirements of the Seveso II directive132 or in the UK the COMAH (Amendment) regulations133 2005. It should be noted that the current carbon dioxide production, storage and handling facilities of the industrial gases sector do not fall under COMAH.
However this document recommends, as with all hazards, debated or not, that competent engineering and the ALARP approach to risk abatement and management and the proper consideration of all legislation, particularly COMAH, is the key to safe delivery of these projects.
Like ‘dangerous substance’, ‘dangerous fluid’ also has a specific legislative meaning in terms of the Pipeline Safety Regulations 1996134. The term ‘dangerous fluid’ is used in the regulations to indicate that pipelines carrying a dangerous fluid are to be considered major accident hazard pipelines.
Dangerous fluids are described as:
- A fluid which:
- is flammable in air;
- has a boiling point below 5 °C, at 1 bar absolute, and
- is, or is to be conveyed in, the pipeline as a liquid.
- A fluid which is flammable in air and is, or is to be conveyed in, the pipeline as a gas at above 8 bar absolute.
- A liquid which has a vapour pressure greater than 1,5 bar absolute when in equilibrium with its vapour at either the actual temperature of the liquid or at 20 °C.
- A toxic or very toxic fluid which:
- is a gas at 20 °C and 1 bar absolute, and
- is, or is to be, conveyed as a liquid or a gas.
- A toxic fluid which:
- at 20 °C has a saturated vapour pressure greater than 0,4 bar, and
- is, or is to be, conveyed in the pipeline as a liquid.
- A very toxic fluid which:
- at 20 °C has a saturated vapour pressure greater than 0,001 bar; or
- is, or is to be, conveyed in the pipeline as a liquid at a pressure greater than 4,5 bar absolute.
- An oxidising fluid which is, or is to be, conveyed as a liquid.
- A fluid which reacts violently with water.
- For the purpose of this definition:
- a liquid is oxidising, and
- a fluid is toxic or very toxic, or reacts violently with water.
- Classified, pursuant to regulation 5 of the Chemicals (Hazard Information and Packaging for Supply) Regulations 2009, as, as the case may be, oxidising, toxic, very toxic or as reacting violently with water.
The above descriptions include carbon dioxide in a number of ways by being toxic and by the classification as a ‘dangerous substance’ under the CHIP regulations.
In considering this classification the implications are significant on the pipeline design process with specific criteria that must be met including emergency shut off valves, consideration of incident prevention, accident planning and specific planning and permitting requirements.
The phases of carbon dioxide are discussed at length through out this text. But the definition of supercritical and Figure 1 shows the phase diagram for carbon dioxide. The fluid state above critical pressure is referred to as the dense phase, above both critical pressure and temperature, supercritical. Whilst the term supercritical is to specific conditions, dense phase is an umbrella terminology, and encompasses supercritical state and liquid state.needs to be considered.
|AGA:||American Gas Association|
|API:||American Petroleum Institute|
|ASME:||American Society of Mechanical Engineers|
|ASTM:||American Society for Testing and Materials|
|BCGA:||British Compressed Gases Association|
|BLEVE:||Boiling Liquid Expanding Vapour Explosion|
|CCGT:||Combined cycle gas turbine|
|CCS:||Carbon capture and storage|
|CFR:||Code of Federal Regulations|
|CGA:||Compressed Gas Association|
|CONCAWE:||Conservation of clean air and water in Europe|
|COSHH:||Control of substances hazardous to health|
|Critical point:||the temperature and pressure point above which carbon dioxide gas and liquid phases cannot exist as separate phases|
|DMEPEG:||Dimethyl Ether of Polyethylene Glycol|
|Dry ice:||solid carbon dioxide|
|DWTT:||Drop Weight Tear Testers|
|EAF:||Electric Arc Furnace|
|ECBMP:||Enhanced Coal Bed Methane Production|
|EGR:||Enhanced Gas Recovery|
|EIGA:||European Industrial Gases Association|
|EOR:||Enhanced Oil Recovery|
|EOS:||Equations of State|
|ESOV:||Emergency Shut-off Valve|
|EU SACS:||European UnionCarbon Dioxide Storage Programme|
|FGD:||Flue gas desulphurisation|
|HSE:||Health and Safety Executive|
|HSL:||Health and Safety Laboratory|
|IGC Code:||International Gas Carrier Code|
|IIR:||Butyl isobutene isoprene rubber|
|IPCC:||Intergovernmental Panel on Climate Change|
|LNG:||Liquified Natural Gas|
|LOC:||Loss of Containment|
|LPG:||Liquified Petroleum Gas|
|MAOP:||Maximum allowable operating pressure|
|MMSCFD:||Million standard cubic feet per day|
|MSS:||Manufacturers Standardisation Society|
|NACE:||National Association of Corrosion Engineers|
|NFPA:||National Fire Protection Association|
|NIOSH:||National Institute for Occupational Safety and Health|
|NIST:||National Institute of Standards and Technology|
|NORSOK:||Norsk Sokkels Konkuranseposisjon - Standards developed by the Norwegian Technology Centre|
|OSHA:||Occupational Safety and Health Administration|
|PHMSA:||Pipelines and Hazardous Materials Safety Administration|
|ppmvd:||Parts per million volumetric dry|
|PSR:||Pipeline Safety Regulations|
|RGD:||Rapid Gas Depressurisation|
|ROSOV:||Remotely Operated Shut Off Valve|
|SACROC:||Scurry Area Canyon Reef Operators Committee|
|SCADA:||Supervisory Control and Data Acquisition|
|SLOD:||Significant likelihood of death|
|SLOT:||Specified level of toxicity|
|Sublimation point:||a temperature/pressure combination at which solid can vaporise directly into gas e.g. −78,5°C at 1atmosphere|
|Supercritical:||above the critical point where carbon dioxide has some characteristics of a gas and some of a liquid|
|Triple point:||the temperature & pressure where carbon dioxide exists as a gas, liquid and solid simultaneously|
|T-s diagram||Temperature-entropy diagram|
|UHMWPE||Ultra High Molecular Weight Polyethylene|
|UN-IMO||United Nations International Maritime Organisation|
127‘The Chemicals (Hazard Information and Packaging for Supply) Regulations, 2009’, Statutory Instrument No. 716.
128‘UN Recommendations on the Transport of Dangerous Goods, Model Regulations’, 15th Edition, 2007.
130 ACGIH . Carbon dioxide. In: Documentation of the threshold limit values for substances in workroom air. 3rd ed. Cincinnati, OH: American Conference of Governmental Industrial Hygienists, p. 39.
132‘Directive on the control of major-accident hazards involving dangerous substances’ (96/82/EC).
133 ‘The Control of Major Accident Hazards (Amendment) Regulations 2005’ Statutory Instrument No. 1088.
134‘The Pipelines Safety Regulations 1996’, Statutory Instrument No. 825.