Dealing with refrigerants of any kind holds a legal requirement that such persons be authorised to do so.
Johann asks: Grant, there is talk on hydrocarbon refrigerants, the flammability aspect and required training, but what of R32? Surely some training is required as at the end of the day R32 does fall into the A2L category. Can you give some indication as to safe working practice for R32.
Hi Johann, yes you are absolutely correct. It does seem that R32 units are being supplied to installers who do not have the necessary knowledge to deal with the flammable refrigerants.
Having said that, it is a legal requirement under the OHS act (Pressure Vessel Regulation) that any person working with refrigerants needs to be an authorised person. As an authorised person, he/she will have received training and will have been assessed as competent for working with refrigerants including the hydro carbons and R32 refrigerants.
R32 is included in the safe handling of refrigerants course offered nationally under the South African Refrigeration and Air Conditioning Contractors Associations control (SARACCA).
Looking into some of the safe working practices for R32 refrigerant, the following can be used as a guide.
Good practice in this regard should be:
- That compliance with regulations shall be observed.
- The length of pipe-work shall be kept to a minimum.
- You should protect the pipe work from damage that may cause a leak.
- Servicing shall only be performed as recommended by the equipment manufacturer.
- Maintenance and repair shall be carried out by or under the supervision of the person competent in the use of flammable refrigerants.
- Servicing shall be performed as per manufacturer’s specifications.
- Maintenance staff and others working in the local area shall be informed on the nature of work being carried out.
- Working in confined spaces should be avoided.
- The area around the workspace should be cordoned off.
- Remove flammable materials from the work area.
- Ensure that the leak detection equipment being used is suitable for use with flammable refrigerants.
- Appropriate fire extinguishing equipment shall be available at hand. Have a dry powder or CO₂ fire extinguisher adjacent to the charging area.
For any work that needs to be conducted on a system that utilises a flammable refrigerant we need to implement some safety measures and safety checks in order to reduce the risk of ignition.
The charge size is relative to the room size within which the refrigerant unit is installed. To put this simply, should a catastrophic leak occur into the refrigerated space, the concentration of the refrigerant when mixed with air shall be below the lower flammability limit, which for R32 is 14%.
It is interesting to note that;
International Standard ISO 817:2014, segregates the flammability of refrigerants into 4 categories as follows: no flame propagation (Class 1), lower flammability (Class 2L), flammable (Class 2) and higher flammability (Class 3).
In general language these classifications are called Non-Flammable, Mildly Flammable, Flammable and Highly Flammable. R32 falls into the ‘lower flammability’ or Class 2L ‘mildly flammable’ category.
Any refrigerant and air mixture that is capable of self-propagating a flame falls into one of the three flammable categories. Class 2L refrigerants present the lowest risk of the flammable categories and are defined by having a burning velocity of less than 10cm per second. The characteristic of this low burning velocity is that the flame front does not propagate readily in a horizontal direction.
This is because the convection rise due to combustion creates a higher velocity than the burning velocity. This effectively means that a Class 2L refrigerant is not explosive if ignited because the flame only propagates in an upwards direction from the ignition point and not rapidly outwards in all directions.
The burning velocity of R32 is at 6.7 cm/s (0.24 km/h). In comparison, the burning velocity of ammonia is 7.2 cm/s, butane is 46 cm/s and hydrogen is 317 cm/s. The burning velocity of a gas is the speed of the flame front relative to motionless gas. The actual flame speed can be several times higher due to the expansion of combusting gas in combination with the burning velocity. This is especially applicable to A2 and A3 refrigerants as their higher heat of combustion generates rapid expansion and turbulence to dramatically increase the flame speed.
For a gas mixture to ignite, three conditions must be met.
The concentration of the flammable gas must lie between the Lower and Upper Flammability Limit (LFL and UFL) for the particular gas. For R32 this is between 14% volume (300 grams/m3) and 29% volume (620 grams/m³). It should also be noted that 14% concentration of any foreign gas in air is the accepted oxygen deprivation safety limit.
The second requirement is that the flammable gas mixture must have a velocity lower than 3 to 4 times its burning velocity (6.7 cm / sec for R32). In the case of a wall mounted split system, because R32 is heavier than air any leaked refrigerant leaving the unit will exceed 4 times its burning velocity due to gravity within 40cm. Furthermore, measurements and computational fluid dynamic models has shown that even a rapid R32 leak of 1 000 grams in one minute will not present a flammable mixture outside of the wall unit due to dilution and the falling velocity of the refrigerant.
The third requirement for ignition to take place is an ignition source of sufficient energy. R32 cannot be ignited by the usual static electricity we experience. Tests by independent laboratories in Japan and the US have demonstrated that sparks from light switches or contactors in residential appliances do not generally have sufficient energy to ignite R32. Therefore, the most likely source of ignition in a residential application is an open flame such as a candle, combustion heater or gas cooker top.
Consequently, if an accidental release of R32 refrigerant occurs from a cylinder or piping, the velocity will be too high to ignite near the release point and the concentration will be too low where the velocity becomes low enough. So, ignition of R32 is difficult even if it is attempted intentionally.
Johann, what do we get out of this? Well, yes, R32 is mildly flammable and precautions need to be taken. Yes, by law, persons working with refrigerants in South Africa do need training and need to be registered to use R32 and any other refrigerant for that matter.
Thanks for the question Johann, In the next issue I shall look into some of the practical aspects for working with R32 refrigerant.
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