New Refrigerants Impact Standards And Codes
Carrier Engineering NewsletterVolume 3, Issue 2New Refrigerants Impact Standards and CodesThe function of refrigerant as a fluid used for heat transfer has not changed since thedevelopment of the first refrigerating system. Today, as in that first system, the refrigerantabsorbs heat and transfers it at a higher temperature and a higher pressure, usually with aphase change. However, as the heating, ventilating, and air-conditioning (HVAC) industryhas evolved and expanded, refrigerants also have changed over the years, mainly inresponse to safety and environmental concerns. Now the industry is moving to a new setof refrigerants developed in the last five years to address climate change issues. Thisnewsletter will describe the benefits and challenges presented by these new refrigerantsand discuss the current state as well as changes in the standards and codes that guide theapplication of refrigerants in HVAC equipment.Historical PerspectiveIn the early days of the industry, the refrigerants usedwere toxic and/or flammable (e.g. methyl chloride, sulfurdioxide). The search for a new refrigerant with theappropriate chemical properties led to the developmentin 1930 of a new refrigerant, dichlorodifluoromethane(CFC), which would later become known as R-12.With R-12, the industry now had a chemical that was lowin toxicity, non-flammable, compatible with mineral oil andvery stable. Use of this refrigerant eventually led to thedevelopment of additional fluorocarbons for specificapplications. Eventually, R-11 (trichlorofluoromethane)became the primary refrigerant in large water-cooledchillers, R-12 in household refrigerators and mobile airconditioning, and R-22 (chlorodifluoromethane) in unitaryequipment for residential and commercial applications.Blends of fluorochemicals were also developed forcommercial refrigeration (e.g. R-500, which is a mixtureof R-12 and R-152a).In the 1970s, it was found that the chlorofluorocarbons(CFCs) were remaining in the atmosphere much longerthan anyone expected. The CFCs would eventually becarried up to the lower levels of the stratosphere wherethey would react with the ozone found there and breakdown the protective ozone layer that shields the earthfrom harmful ultraviolet radiation from the sun. As a resultof this discovery, the members of the United Nationsdeveloped the Montreal Protocol on Substances thatDeplete the Ozone Layer, which called for the phase-outof ozone-depleting substances. The halogenatedrefrigerants (those compounds that include fluorineor chlorine) were divided into three categories based ontheir ozone depletion potential. The chlorofluorocarbons Carrier Corporation 2015(e.g. CFC-11 and CFC-12) with the longest atmosphericlifetime and highest ozone depletion potential werephased out first, followed by the hydrochlorofluorocarbons,or HCFCs (e.g. HCFC-22, HCFC-123). In developedcountries, production and consumption of HCFCs wouldbe reduced 90% from the base level on January 1, 2015.Production and consumption of HCFCs for use in newequipment will be prohibited on January 1, 2020 with0.5% of the baseline being allowed for servicing ofexisting refrigeration and air-conditioning equipment untilJanuary 1, 2030. On January 1, 2030 production andconsumption of HCFCs will be prohibited. Some nationsaccelerated this schedule. Developing countries, asdefined in Article 5 of the Montreal Protocol, have anadditional 10 years to phase out the HCFCs. Actionstaken under the Montreal Protocol have led to decreasesin the atmospheric abundance of controlled ozonedepleting substances (ODSs), and are enabling thereturn of the ozone layer toward 1980 levels.1Executive Summary of the Assessment for Policy Makers of the 2014Scientific Assessment of Ozone Depletion.1www.carrier.com/commercial
The HVAC industry transitioned to hydrofluorocarbons, orHFCs (e.g. HFC-134a, HFC-410A), which do not depletethe ozone layer and thus are not part of the phase-outunder the Montreal Protocol.of hydrocarbons, carbon dioxide, and hydrofluoroolefins(HFOs), which were developed in the last five years.They all present the industry with new challenges.HFOs and Natural RefrigerantsWhile non-ozone depleting, HFCs, like the CFCs theyreplaced, are greenhouse gases (so-called because theytrap heat in the atmosphere). The Kyoto Protocol, aninternational agreement linked to the United NationsFramework Convention on Climate Change (UNFCC),specifically identified these refrigerants and called forreductions in emissions of greenhouse gases, includingHFCs. Although the Kyoto Protocol has expired,negotiations are underway for a new internationalagreement to limit greenhouse gases under the UNFCC.In addition, several proposals have been introduced toamend the existing Montreal Protocol for a global HFCphase-down agreement. In the meantime, some countriesand regions are passing regulations limiting the use ofHFCs in order to reduce their emissions of greenhousegases. Although their use in the future may be limited,HFCs (e.g. HFC-134a, HFC-410A) are not being phasedout. The HFCs are the best energy-efficient refrigerants forsome applications and there will continue to be arequirement for HFCs in order to meet the demand for airconditioning and refrigeration.The move to refrigerants with low global warming potential(GWP)2 has forced the industry to re-evaluate refrigerantspreviously considered unacceptable due to high pressureor flammability concerns. In order to reduce theatmospheric lifetime of the refrigerants, the industry hasdeveloped a new class of compounds calledhydrofluoroolefins or HFOs. These are new chemicals thathave very short atmospheric lifetimes and therefore verylow GWP. They were developed to replace HFCs that havehigher GWP values.New air conditioning and refrigeration products are beingdeveloped to use either the new HFOs or naturalrefrigerants like hydrocarbons (e.g. propane, R-290, andisobutane, R-600a) or carbon dioxide (CO2). Some of theselow GWP refrigerants are flammable and proper safetyprecautions must be taken to ensure the refrigerant will notignite in the event of a leak. Safety standards and modelcodes will have to consider the lower flammable limit of therefrigerant, amount of charge, risk of refrigerant leak, thearea where a leaked refrigerant could occur and thepresence of ignition sources as they develop requirementsfor the safe use of these flammable refrigerants.The chart in Figure 1 shows the transition in refrigerantssince 1930. The fourth generation of refrigerants consistsFigure 1 – Transition in Refrigerants from 1930s to PresentGlobal-warming potential (GWP) is a relative measure of how much heat a greenhouse gas traps in the atmosphere. It compares the amountof heat trapped by a certain mass of the gas in question to the amount of heat trapped by a similar mass of carbon dioxide. All GWP valuesin this document were obtained from either the 4th Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) or the U.S.Environmental Protection Agency (EPA).2 Carrier Corporation 20152www.carrier.com/commercial
Standards and CodesFigure 2 – Safety Classification of Refrigerants inASHRAE Standard 34Industry standards play an important part in worldwiderefrigerant regulation and application. AlthoughASHRAE Standard 34, which defines refrigerant safetyclassifications, has been updated, ASHRAE Standard 15,the equipment safety standard that relies on and refers tothese classifications, has not yet been revised. Revisionsto ASHRAE Standard 15 are in progress. The equipmentsafety standard must be revised before any updates to themodel codes can be tyFollowing is a discussion of some of the changes to thesestandards and how they will affect the use of refrigerants inthe HVAC industry.ASHRAE Standard 34, Designation andSafety Classification of RefrigerantsASHRAE Standard 34 assigns the refrigerant numbers anddetermines the proper safety classification based on toxicityand flammability CR-507AR-744 Carbon DioxideB1R-123Lower ToxicityHigher ToxicityToxicity*A2L and B2L are lower flammability refrigerants with a minimum burning velocityof 10 cm/s.ASHRAE defines two safety classifications for toxicity:Class A signifies refrigerants that are of lower toxicity andClass B signifies refrigerants that are of higher toxicity. Forflammability, there are three classifications and one subclassification. The three main flammability classificationsare: Class 1, for refrigerants that do not propagate a flamewhen tested as per the standard; Class 2, for refrigerants thatare of lower flammability; and Class 3, for highly flammablerefrigerants, like the hydrocarbons. The safety classificationmatrix (Figure 2) was recently updated to include a newflammability Subclass 2L, for flammability Class 2 refrigerantsthat burn very slowly. Some HFOs, which have very lowglobal warming potential, are mildly flammable and areclassified as A2L. This indicates they are of lower toxicity andhave a low burning velocity of 10 cm/sec.mildly flammable classification, it is suitable for new chillerapplications but cannot be used in existing equipment. Thisrefrigerant has a low GWP value of 0.97.HFO-1233zd(E) (Safety Class A1) is of lower toxicity andnon-flammable. This refrigerant was developed for and isbeing used as a blowing agent for polymer foams. Thisrefrigerant has a GWP value of 1.34 and is also beingevaluated for use in new chiller applications as a lowpressure refrigerant that can operate in a vacuum undernormal air conditioning conditions. This application wouldrequire the use of a purge to remove noncondensablesfrom the closed cycle.Hydrocarbons, like propane (R-290) with a GWP valueof 3.3, and isobutane (R-600a) with a GWP value of 3.0,have very good thermodynamic properties, but are highlyflammable and are listed as Safety Class A3. Other than inindustrial applications, their use is restricted to hermeticallysealed systems with very small charge sizes.Following is a description of some of the low GWPrefrigerants and other alternative refrigerants beingconsidered by the industry, along with their ASHRAEStandard 34 classifications and direct GWP values:HFC-32 (Safety Class A2L) is a component of R-410A andis being considered as an interim substitute for R-410A inunitary equipment. This mildly flammable refrigerant has ahigher vapor pressure than R-410A. With a GWP value of675, the global warming potential of HFC-32 is lower thanthat of R-410A (GWP of 2088) but still too high for long termuse under current regulatory proposals.Carbon dioxide (R-744 or CO2) works well in someapplications, particularly refrigeration, but its high pressureslimit its use elsewhere. Listed as Safety Class A1, carbondioxide is currently being used in commercial refrigerationsystems in northern Europe and in marine container units.The GWP value of carbon dioxide is 1.0.HFO-1234yf (Safety Class A2L) was first commercializedas a replacement for HFC-134a in automobile airconditioning. This refrigerant is of lower toxicity and mildlyflammable, with a GWP value of 0.31.Ammonia (R-717 or NH3) works well in some applications,but its mild flammability and toxicity require mitigationcontrols and limit its application. It is listed in ASHRAEStandard 34 as Safety Class B2L. Ammonia has historicallybeen used in large refrigeration systems and otherindustrial applications. Ammonia is not a greenhouse gasand therefore has no GWP value.HFO-1234ze(E) (Safety Class A2L) is being evaluated foruse in new chiller applications to replace HFC-134a and isplanned for introduction in Europe in 2015. Due to the Carrier Corporation 2015No FlamePropagationA3R-290 PropaneR-600a Isobutane3www.carrier.com/commercial
DIRECT VS INDIRECT GREENHOUSE GAS EMISSIONS: THE IMPACT OF ENERGY EFFICIENTOPERATION ON CLIMATE CHANGEWhen evaluating the effect of greenhouse gases on climatechange, keep in mind that refrigerants are only part of thestory. In 2013, fluorinated gases, which include HFCs,accounted for 3% of U.S. greenhouse gas emissions(direct effect), while carbon dioxide, which is emitted fromfossil fuel burning power plants (indirect effect), accountedfor 82% of U.S emissions, as shown in the pie chart.addition, the U.S. Department of Energy is increasingminimum energy efficiency requirements for air conditioningand refrigeration systems.U.S. Greenhouse Gas Emissions (2013)Methane10%Nitrous Oxide5%Fluorinated Gases3%In order to reduce emissions of greenhouse gases wemust not only find new low GWP refrigerants but alsodesign equipment that is more energy efficient to reduceconsumption of electricity, most of which is generated byburning fossil fuels, leading to emissions of carbon dioxide.The total electricity consumption of the equipment must beconsidered, including the compressor, fans, and pumps.Appropriate sizing of equipment is important to closelymatch capacity to load and avoid excessive compressorcycling. Any factor that increases energy usage contributesto the indirect effect that equipment operation has onclimate change.Choosing low GWP refrigerants that result in higher energyconsumption does not help reduce climate change. InCO2 82%7.5.2 Applications for Human Comfort. Group A2, A3,B1, B2, and B3 refrigerants shall not be used in highprobability systems for human comfort.The introduction of the flammability classification of A2Lin ASHRAE Standard 34 will require related changes toequipment safety standards and building codes. Thesechanges are still in progress, as described below.7.5.3 Higher Flammability Refrigerants. Group A3 andB3 refrigerants shall not be used except where approvedby the AHJ (authority having jurisdiction).ASHRAE Standard 15, SafetyStandard for Refrigeration SystemsUL 1995 Heating and Cooling EquipmentThis standard specifies safe design, construction,installation, and operation of refrigeration systems. Thisstandard references the safety classifications in ASHRAEStandard 34. The committee responsible for maintainingASHRAE Standard 15 has established an ad hoc workinggroup to develop revisions to the standard to address theuse of mildly flammable refrigerants listed in ASHRAEStandard 34 as A2L. The first draft was circulated for anadvisory public review in 2011 in order to obtain commentsfrom industry representatives outside the committee. Thecommittee is now preparing a revised document, taking intoconsideration the comments received along with recentlycompleted risk assessments, potential ignition sources,ventilation requirements and leak detector reliability.The UL Standard for Heating and Cooling Equipment(UL 1995) is being replaced by IEC 60335-2-40, withU.S. deviations, and will include restrictions for the useof flammable refrigerants in stationary air-conditioningand refrigerating equipment. Standard IEC 60335-240 is under revision and a public review document willlikely be released later this year for global review. Oncecompleted it will be reviewed and modified as needed forimplementation in the U.S., Canada and Mexico.Model CodesOnce ASHRAE has published the requirements forapplication of the new mildly flammable refrigerants inStandard 15, ASHRAE will submit a code change proposalto the model codes in the United States. The codescurrently include some of the new refrigerants that areclassified as A2L or B2L in ASHRAE Standard 34 but theyare classified as flammability Class 2 in the codes untilrequirements for their safe use have been established.Currently, ASHRAE Standard 15-2013 prohibits the useof flammable refrigerants in systems for human comfortwhere leaked refrigerant will enter the occupied space(see sections 7.5.2 and 7.5.3 and excerpts below) andhas no provisions for refrigerants with a flammabilityclassification of 2L, therefore refrigerants in this classmust be treated as Class 2. Carrier Corporation 20154www.carrier.com/commercial
International Mechanical Code (IMC)Uniform Mechanical Code (UMC)The 2015 International Mechanical Code (IMC), usedin most jurisdictions in the US, handles the safetyclassification as shown below in an excerpt from Table1103.1 of the Refrigerant System Classification Section(Figure 3). Refrigerants listed as A2L in ASHRAEstandard 34 are listed as Class 2 in the IMC becauserequirements for the use of Class A2L refrigerants arestill in development. A footnote on these refrigerants letsthe users of the IMC know that the safety classificationin ASHRAE Standard 34 is A2L. ASHRAE will submit aproposal to change the classification in Table 1103.1 toA2L once ASHRAE Standard 15 has been updated withrequirements for use of the refrigerants. The code is on a3-year revision cycle and the deadline for submitting codechange proposals for the 2018 IMC has already passed,therefore, the earliest this change would come into effectwould be in the 2021 IMC.The Uniform Mechanical Code (UMC), published by theInternational Association of Plumbing and MechanicalOfficials (IAPMO), also includes a table of refrigerants inChapter 11. The UMC is also on a 3-year revision cycleand ASHRAE routinely submits code change proposalto add refrigerants to Table 11-1 that have been addedto the ASHRAE Standard since the last code revision.Refrigerants listed as A2L in Standard 34 are listedas Class A2 in the UMC Chapter 11 with a footnoteindicating that the safety classification in Standard 34is A2L.State and Local Code AdoptionOnce provisions for use of mildly flammable refrigerantsare in the model codes they must be adopted by statesand local jurisdictions. The model codes are updated on a3-year cycle and the deadline for submitting code changeproposals for the 2018 IMC has already passed, so theearliest that requirements for the use of A2L refrigerantscould appear in the IMC is 2021. The deadline forsubmitting code change proposals for the 2018 UniformMechanical Code (UMC) is in January of 2016 so thereis still a possibility of changing that code although itis unlikely that ASHRAE will have an amendment toStandard 15 ready in that timeframe.Section 1104, System Application Requirements restrictsthe amount of a refrigerant allowed in a building outsideof a machine room based on the amount of refrigerantper occupied space listed in Table 1103.1. For flammablerefrigerants, the amount of refrigerant per occupied spaceis based on preventing the refrigerant concentration fromreaching 25% of the lower flammable limit (LFL) if theentire charge were released into the room. Since the LFLof Class A2L refrigerants is higher than the LFL of ClassA2 refrigerants, the amount of refrigerant allowed peroccupied space will increase.Figure 3 – Excerpt from the International Mechanical CodeSection 1103 Refrigeration System Classification1103.1 Refrigerant classification. Refrigerants shall be classified in accordance with ASHRAE 34 as listed in Table 1103.1[F] TABLE 1103.1 REFRIGERANT CLASSIFICATION, AMOUNT AND OELf. The ASHRAE Standard 34 flammability classification for this refrigerant is 2L, which is a subclass of Class 2. OEL — Occupational Exposure Limit Carrier Corporation 20155www.carrier.com/commercial
MAPPING THE CODE REVISION PROCESSThere is a significant amount of work underway to modify standards and codes globally to allow the use of the newrefrigerants, but progress takes time as all interested parties must reach consensus on the changes. The chart belowprovides an example of the complexity of the process.Regulationsare flammable. Most, with the exception of HFC-32, arehighly flammable, Class A3 refrigerants. HFC-32 is listed inASHRAE Standard 34 as a Class A2L refrigerant. Approvalis only for the application shown. Details of the rule canbe found on the EPA web site: http://www.epa.gov/ozone/snap/index.htmlIn addition to changes in safety standard and codes,governmental regulations must also be considered.U.S. Environmental Protection Agency(EPA) Significant New Alternatives Policy(SNAP) ProgramThe EPA also has a proposed rule that would removesome high GWP refrigerants from the list of acceptablesubstitutes used as aerosol propellants, and as refrigerantin motor vehicle air-conditioning and some food refrigerationequipment. This does not impact the use of theserefrigerants in HVAC equipment.In the U.S., the EPA must approve the refrigerant for usein each application. Recently the EPA published a rule thatadds low GWP refrigerants to the approved list for someapplications as shown in Figure 4. All of the refrigerants Carrier Corporation 20156www.carrier.com/commercial
Figure 4 – EPA-Approved Applications for some Low GWP 441AHFC-32633 -AloneVendingHFC Control MeasuresVery LowTemp RefHeatTransferHome ACSelf-Containedphase-down of HFC production and consumption over thenext 20 years resulting in an eventual reduction of HFCproduction of 85% over baseline levels (see Figure 5).The proposal has not yet overcome objections from severalnations, but seems to be gaining momentum.The European Union has passed regulations requiringa phase-down of HFCs beginning January 1, 2015 witha cap on the quantity of HFCs that can be placed on themarket. The first step-down occurs in 2016 with a 7%reduction from the cap, leading ultimately to a reductionof 79% by 2030. In addition there are bans on somehigh GWP HFCs in specific applications that take effectbetween now and 2025.This year, HFC phase-down proposals have also beensubmitted by India, the European Union, Senegal and thePacific Island States. In addition, the African Group hascalled for formation of a contact group to discuss a programunder the Montreal Protocol to phase down HFCs. All theseproposals will be considered in the negotiations among theparties to the Montreal Protocol.The U.S., Canada and Mexico have submitted a proposalto the parties to the Montreal Protocol on Substances thatDeplete the Ozone Layer that would require a steppedFigure 5 – Proposal for Amendment to the Montreal Protocol Stepped Phase-Down of HFC Production and Consumption Carrier Corporation 20157www.carrier.com/commercial
RESEARCH PROJECTS ASSIST WITH STANDARDS DEVELOPMENTASHRAE and AHRI have research programs underwayto assist with standards development process. Theeight projects below are either underway or have beencompleted recently: AHRI 8016, Risk Assessment of Rooftop Units UsingA2L Refrigerants. ASHRAE RP-1448 -- Ventilation Requirements forRefrigerating Machinery Rooms. AHRI 8004 -- Risk Assessment of Residential HeatPump Systems Using 2L Flammable Refrigerants,T. A. Lewandowski, 2012. ASHRAE RP-1580 -- Study of Input Parametersfor Risk Assessment of 2L Flammable Refrigerants inResidential Air Conditioning and CommercialRefrigeration Applications. AHRI 8006 -- Low Global Warming Potential (GWP)Refrigerants, Phase II: Defining the Configurationsof Residential Air-Conditioning and Heat Pump SystemsUsing Hydrocarbons, Ammonia, Carbon Dioxide, andHFO-1234yf as Refrigerants and Meeting PreviouslyDefined Safety Requirements, W. Goetzler,D. Westphalen, and J. Burgos. ASHRAE RP-1584, Developing Alternative Approachesto Predicting the Laminar Burning Speed of RefrigerantsUsing the Minimum Ignition Energy. ASHRAE 1717-RP, Improve Accuracy andReproducibility of ASTM E-681, Test Method forFlammability Limit Measurement of 2L FlammableRefrigerants. AHRI 8009, Risk Assessment of Refrigeration EquipmentUsing A2L Refrigerants.SummaryRegulations related to climate change will have an impacton several aspects of the HVAC industry. The industry willbe faced with another refrigerant transition as it movesto new low GWP refrigerants and, in some cases, willhave to prepare for the use of flammable refrigerants incommercial, industrial, and residential buildings. Changesto industry safety standards and the model building codeswill be required before these new refrigerants can beimplemented. The use of flammable refrigerants also willrequire changes in service practices to prevent ignition ofthe refrigerant.At the same time, the industry will be working to increaseenergy efficiency of all air-conditioning and refrigerationequipment systems in an effort to minimize the greenhousegases produced by generating electricity to run theequipment. In many cases, these changes will be requiredby energy efficiency standards imposed by the U.S.Department of Energy.As requirements evolve, the industry will look to innovativemanufacturers to provide solutions that can meet thechallenges of efficiency, safety, and environmentalconcerns.Refrigerants with very high GWP, like R-404A, will be thefirst to be replaced with lower GWP options. Other HFCswill be in use longer as the industry investigates the variouslow GWP options that are available. The industry will alsowork to reduce refrigerant charge size in equipment asmuch as possible to minimize the amount of refrigerantused that could ultimately be released to the atmosphere.In addition to developing new equipment, the industry mustaddress how to retrofit existing equipment to use lowerGWP refrigerants. Carrier Corporation 2015Carrier continuously invests in research and developmentand is committed to deploying products and technologiesthat minimize environmental impact while serving customerneeds. This is equally true for refrigerants. While not everyapplication may have the same refrigerant solution, Carrierwill have the right refrigerant solution for every application.This paper is provided for informational and marketing purposes only and shallnot be deemed to create any implied or express warranties or covenants withrespect to the products of Carrier Corporation or those of any third party.8www.carrier.com/commercial
to ASHRAE Standard 15 are in progress. The equipment safety standard must be revised before any updates to the model codes can be made. Following is a discussion of some of the changes to these standards and how they will affect the use of refrigerants in the HVAC industry. ASHRAE Standard 34
The International Symposium on New Refrigerants and Environmental Technology 2018 . Hitoshi Hashimoto (Refrigerants related to International Standards WG, JRAIA) Overview: Risk Assessment of Mini-split Air Conditioners using A3 Refrigerant . Development of low-GWP refrigerants for low temperature applications Robert E Low (Mexichem UK Ltd.) .
2. Refrigerant mixtures/blends (a) Based on the number of pure components, i.e., binary / ternary /quaternary (b) Azeotropic /near azeotropic / zeotropic (non-azeotropic) 2.2.1 Pure Refrigerants (Single Component Refrigerants) Natural refrigerants are those substanc
of CFC refrigerants and conventional mineral oils generally get a rating of 3, which is the limit of acceptability. The new refrigerants and lubricants must outperform those being replaced in order to be considered acceptable. After the visual ratings were obtained, sample tubes were opened and the lubricant and refrigerant were analyzed.
Flammable Refrigerants and Safety in Automotive Applications Preface This guide is the result of a joint project between Refrigerant Reclaim Australia, VASA and GHD Engineering to study the management of health and safety risks associated with the use of flammable gases, including refrigerants
(MSDS) for safety information on the specific Genetron Refrigerant you will use. GENETRON HFC Refrigerants. GENTRON PERFORMAX LT (R-407F), GENETRON AZ-50 and GENETRON 404A are HFC refrigerants and are not scheduled for phaseout under current law. Descriptive information including refrigerant type, ASHRAE number,
Refrigeration & air conditioning refrigerants Foaming & insulation . Low-GWP Equipment Refrigerants Performance evaluation of equipment Performance evaluation of refrigerants Risk assessment in real-use situations . TEMP Alternatives to R410A and R404A Alternatives to R32
ASHRAE 34 20 ASHRAE Standard 34 –Designation and Safety Classification of Refrigerants Higher Flammability A3 B3 Lower Flammability A2 B2 A2L* B2L* No Flame Propagation A1 B1 Lower Toxicity Higher Toxicity All refrigerants can be combusted when put into a high-energy situation such as a fi
Workbook 8 Skeletal anatomy 8.3erminology T There is a conventional terminology of anatomy which has been adopted throughout the world in order to avoid confusion. This terminology helps to describe the body parts relative to one another. Physiotherapists and doctors often use these terms to describe conditions that you will
