By Barney Richardson

Last month we talked about the flammable refrigerants like R290 and R600a which are classified as group A3. R-32 is classified as group A2L, only with lower flammability.

The ‘A’ designates a refrigerant with a lower toxicity at an occupational exposure limit (OEL) of 400 ppm or greater. The ‘B’ designation is the higher toxicity where refrigerants have an occupational exposure limit of less than 400 ppm.

The F-gas refrigerants we have all been used to for air conditioning and refrigeration such as R22, R134a, R404 and R410a are all classed as A1 low toxicity and flammability. But why can’t we use them anymore? It’s all about global warming and ozone depletion, therefore the move to natural refrigerants.

For interest Ammonia (R717) is classified as B2L which has a flammability under certain conditions and is toxic but warns you of its presence by the smell. Ammonia, a great refrigerant, has been used for many years and will continue to be used in low charge systems.

There are many skilled specialist practitioners working on Ammonia systems. New to us in supermarkets is Carbon Dioxide (R744) which is classed as A1 with only low toxicity and the potential to displace Oxygen in confined places. CO2 also requires specialist skills and experience.

Table 1: Classification of refrigerant safety groups (ASHRAE Standard 34-2019).

High Flammability

A3

B3

Flammable

A2

B2

Low Flammability

A2L

B2L

No Flame propagation

A1

B1
 

Low Toxicity

High Toxicity

There is now the introduction of flammable refrigerants in domestic refrigerators and beverage coolers into South Africa which places a greater responsibility for skills on the R290 and R600a refrigerants. There is also R32 – soon to be introduced in room air conditioners.

While attending to repairs and maintenance, there is the risk of a flammable refrigerant being released during recovery or charging. The risk of an ignition is always there – for example any electrical sources. Certainly smoking or allow anyone to smoke near your work area must be strictly avoided. This leakage is certainly possible when connecting and/or disconnecting gauge hoses for recovery or charging.

It would be wise to have at least a 2-metre temporary flammable work zone in all directions of an outdoor condensing unit, or if indoors, from the refrigeration appliance. For larger refrigeration systems using a flammable refrigerant the safe distance allowed should be even greater. If the area is a confined space, for example within a house or building, this must be well ventilated. Practitioners should always consider the work area of an installation or maintenance as a flammable hazard zone. This zone must be free from all forms of ignition.

Handling and storage requirements for flammable refrigerant cylinders are similar to those used for liquefied petroleum gas (LPG). As a normal rule, the maximum quantity of gas in cylinders stored or used indoors in residential premises must not exceed 10kg in weight or be less. It should be remembered that flammable refrigerants usually come in small cylinders and the allowable charges you would encounter are in the hundreds of grams

Only special vacuum pumps suitable for flammable refrigerant gases must be used. A two stage vacuum pump is recommended for evacuating a system, Always try to pull a vacuum to between 200-500 microns. Electronic vacuum gauges, if used, must be designed for use with flammable refrigerants.

“Handling and storage requirements for flammable refrigerant cylinders are similar to those used for liquefied petroleum gas (LPG).”

Because of the very small charges of flammable refrigerants, the charge volumes can only be measured with an accurate scale. It is therefore important to control and monitor the refrigerant charge with an accurate weighing scale.

Some do’s and don’ts

  • Always wear appropriate personal protection gear.
  • The storage area for refrigerant cylinders must be well ventilated and free of combustible materials.
  • Keep the cylinders away from sources of heat and out of direct sun, especially in a yard or on a bakkie.
  • Do not store the cylinders near sources of ignition like electrical power outlets, lights and switches or electric motors.
  • Power tools and chargeable hand drills and screwdrivers, vacuum pumps and recovery equipment must be rated flame proof and for hazardous area use.
  • Any potential ignition sources must be at least 3 metres away.
  • Never lay refrigerant cylinders on their side and protect the cylinders from falling or being knocked over.

Click here for the latest issue of RACA Journal 

 

Post Views: 122