Regular technicals
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By: Grant Laidlaw
Welcome to the Solutions page
Many people ask for assistance in the understanding of theoretical and practical aspects of the indus-try. I will endeavour to enlighten. We are going back to basics as I have questions coming in that indi-cate that the basic understanding necessary to work in industry is not in place.
Clement asks: Hi Grant, We find that some technicians do not know how to deal with the safety aspects of flammable refrigerants. Can you please discuss the use of flammable refrigerants. Thanks.
Hi Clement, I have looked into R290 in previous issues and will now summarise this topic.
Working with flammable refrigerant and cylinders requires strict safety procedures due to their high flammability. Proper training and adherence to safety protocols are critical for anyone handling these refrigerants.
It is recommended that companies and personnel who use hydrocarbon refrigerants either in equipment they manufacture or equipment for which they are responsible, put into place a general strategy to ensure that correct work practices are employed.
Note that the requirements detailed here are generic and not exhaustive, but are intended as a guide only. Additional precautions may be appropriate dependent upon the particular equipment and conditions.
Practical Competence
Any person who is involved with working on or breaking into a refrigerant circuit must be registered as an authorised refrigeration practitioner in the relevant category.
Servicing shall only be performed as recommended by the equipment manufacturer. Maintenance and repair requiring the assistance of other skilled personnel shall be carried out under the supervision of the person competent in the use of flammable refrigerants.
General Approach to Hydrocarbon Refrigerant Handling
All flammable refrigerant gases when mixed with air form a flammable mixture. The effect of ignition of such a mixture can be severe. It is therefore important that the appropriate safety requirements are ob-served at all times when working with flammable refrigerants.
Any equipment used in the process of repair must be suitable for use with flammable refrigerants. All tools and equipment (including measuring equipment) are to be checked for suitability for working on the equipment.
If the installation permits, it is recommended that the equipment be removed from its existing position to a controlled workshop environment suitable for the type of repair where work can be conducted safely.
Safety Checks
Checks to the Area
Prior to beginning work on systems containing hydrocarbon refrigerants, safety checks are necessary to ensure that the risk of ignition is minimised as well as the refrigerant collecting in low-lying areas. For repair to the refrigerating system prior to conducting work on the system, the following precautions shall be complied with:
Work Procedure
Work should be undertaken under controlled procedures so as to minimise the risk of a flammable vapour being present while the work is being performed.
General Work Area
All maintenance staff and others working in the local area should be instructed as to the nature of work being carried out. Work in confined spaces must be avoided. Low-lying areas must be ventilated.
The area around the workspace is to be sectioned off. Ensure that the conditions within the area have been made safe by control of flammable material and ignition sources.
Presence of Fire Extinguisher
Appropriate fire extinguishing equipment shall be available to hand. Have a dry powder or CO2 fire extinguisher adjacent to the charging area.
Checking for Presence of Refrigerant
The area shall be checked with an appropriate refrigerant detector prior to and during work to ensure the technician is aware of potentially flammable atmospheres.
Ensure that the leak detection equipment being used is suitable for use with flammable refrigerants, i.e. non-sparking, adequately sealed or intrinsically safe.
Leak Detection
The following leak detection methods can be used on systems containing hydrocarbons:
• Electronic leak detectors may be used to detect hydrocarbons that are designed to do so. (Detection equipment should be calibrated in a refrigerant-free area.) Ensure that the detector is not a potential source of ignition and is suitable for hydrocarbon refrigerants.
• Leak detection fluids are suitable for use with hydrocarbon refrigerants but the use of detergents containing chlorine should be avoided as the chlorine may react with the refrigerant and corrode the cop-per pipework.
• Oil additives such as those used in fluorescent leak detection systems will operate with hydrocarbons.
• If a leak is suspected from a hydrocarbon refrigerant system all ignition sources should be removed. If a leakage of refrigerant is found which requires brazing, all of the refrigerant shall be removed from the system, or isolated (by means of shut-off valves) in a part of the system remote from the leak.
• Nitrogen should then be purged through the system both before and during the brazing process.
Pipe Connections
Eliminate flared connections or compression fittings wherever possible. Use brazed joints only.
No Ignition Sources
Prior to work taking place, the area around the equipment is to be surveyed to establish any flammable hazards or ignition risks.
No person carrying out work in relation to a refrigeration system which involves exposing any pipe work which contains or has contained flammable refrigerant shall use any sources of ignition in such a manner that it may lead to the risk of fire or explosion.
All possible ignition sources, including cigarette smoking, should be sufficiently far away (2.5 to 3 me-ters) from the site of installation, repairing, maintaining from which flammable refrigerant could be released into the surrounding space.
Ventilated Area
Ensure that the area is in the open or that it is adequately ventilated before breaking into the system or conducting any hot work. A degree of ventilation should continue during the period that the work is carried out. The ventilation should safely disperse any released refrigerant and preferably expel it externally to the atmosphere. Portable fans can be used to disperse the refrigerant. Venting should be done to an outdoor area where it is safe to do so.
Checks to the Refrigeration Equipment
Where electrical components are being changed, they are to be “fit for purpose”, and to the correct specification. At all times the manufacturers maintenance and service guidelines are to be followed. If in doubt consult the manufacturers for assistance.
The following checks should be applied to installations using flammable refrigerants:
• That the charge size is in accordance with the room size within which the refrigerant containing parts are installed.
• That ventilation machinery and outlets are operating adequately and not obstructed.
• Confirm operation of equipment such as refrigerant leak detectors and mechanical ventilation systems.
• If an indirect refrigerating circuit is being used, the secondary circuit should be checked for the presence of refrigerant.
• Ensure that labelling of the equipment continues to be visible and legible.
• Refrigeration piping or components must not be installed in a position where it is likely to be exposed to any substance which may corrode refrigerant containing components.
Checks to Electrical Devices
Intrinsically safe components are the only types that can be worked on while live in the presence of a flammable atmosphere. However, test apparatus should also be of an appropriate rating
Replace only with parts specified by the manufacturer. Other parts may result in the ignition of refrigerant in the atmosphere from a leak.
Check that cabling will not be subject to wear corrosion, excessive pressure, sharp edges or any other adverse environmental effects. This should also take into account the effects of ageing or continual vibration from sources such as the compressor or fans.
Breaking into a System and Charging
When breaking into the refrigerant circuit conventional procedures are used. However, it is important that best practice is followed since flammability is now a consideration. The following procedure shall be adhered to:
• Remove refrigerant
• Purge the circuit with inert gas (Nitrogen)
• Evacuate
• Purge again with inert gas
Once the refrigerant charge is removed the system is then to be “flushed” with Nitrogen to render the unit safe, this process may need to be repeated several times. On no account use compressed air or oxygen for this task.
Flushing is achieved by breaking the vacuum in the system with nitrogen and continuing to fill until the working pressure is achieved, then vent to atmosphere, and finally pulling down to a vacuum.
This process is repeated until satisfied that no hydrocarbons are within the system. When the final Ni-trogen charge is used, the system can be vented down to atmospheric pressure to enable work to take place.
This operation is absolutely vital if brazing operations on the pipework are to take place. Ensure that the outlet for the vacuum pump is not close to any ignition sources and that there is ventilation available.
Charging
Prior to recharging the system it should be pressure tested.
The system must be leak tested on completion of charging but prior to commissioning. A followup leak test should always be carried out prior to leaving site.
The charging of refrigeration systems with hydrocarbon refrigerants is similar to those using traditional refrigerants.
The following additional requirements should be adhered to:
• Ensure that contamination of different refrigerants does not occur when using charging equipment. Hoses or lines are to be as short as possible to minimise the amount of refrigerant contained in them.
• It is recommended that the refrigerant is charged in the liquid phase where possible.
• Ensure that the refrigeration system is earthed prior to charging the system with refrigerant.
• The refrigerant should be weighed into the system using an accurate refrigerant scale
• Label the system when charging is complete. The label should state that hydrocarbon refrigerants have been charged into the system, the quantity and that it is flammable. Position the label in a prominent position on the equipment.
• Extreme care shall be taken not to overfill the refrigeration system. (Note that hydrocarbon charge sizes are typically 40% to 50% of HCFC and HFC charge sizes)
Commissioning
A refrigeration system containing hydrocarbon is commissioned in exactly the same manner as systems containing HFC/HCFC refrigerants.
Ensure that correct marking is applied to the system
Handling Of Cylinders
Hydrocarbon refrigerant is available in various sizes of cylinders. Pressure relief valves are fitted to the cylinders to prevent excess pressure buildup. The cylinders are fitted with off-take valves incorporating a non-return valve.
Safe cylinder handling differs little from other refrigerant cylinders which are as follows:
• Do not remove or obscure official labelling on a cylinder
• Always refit the valve cap when the cylinder is not in use
• Do not expose cylinders to direct sources of heat such as steam or electric radiators
• Do not repair or modify cylinders or cylinder valves
• Always use a proper trolley for moving cylinders even for a short distance – never roll cylinders along the ground
• Take precautions to avoid oil, water and foreign matter entering the cylinder
• If it is necessary to warm the cylinder, use only warm water or air, not naked flames or radiant heat-ers, the temperature of the water or air must not exceed 50°C
Transport Of Cylinders
Ensure compliance with The Road Traffic Regulations as applicable to the transportation of cylinders containing hydrocarbons.
Storage Of Cylinders
Cylinders containing hydrocarbon refrigerants should be stored at ground level, never in cellars or basements. Cylinders should be readily accessible, and stored upright. Cylinders should be preferably stored outside and never stored in residential premises. Cylinders may be stored in commercial and industrial premises according to the following guidelines for storage.
• Quantities stored are to be restricted to no more than 70 kg and stored in specific dedicated areas or cages.
• Access to storage areas restricted to ‘authorised persons only’, and such places shall be marked with notices prohibiting smoking and the use of naked flames.
• Store and use cylinders in dry, well-ventilated areas remote from fire risk
• Static electricity build-up should be avoided.
Clement please see previous issues of the RACA Journal for some more specific details of some of the aspects mentioned in this issue. I hope that this assists you with the usage of flammable refrigerants.
Grant Laidlaw
grant@acra.co.za
REFERENCES:
ACRA
SANS 10147
GIZ
SAFETY STANDARD EN378-1:2017-03