RACA Journal April 2025 RACA_April2025_2 | Seite 43

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HAZARDS OF CARBON DIOXIDE AND SAFETY MEASURES

CO2 is part of many biological processes and naturally occurs in the atmosphere . It is non-flammable and non-toxic in small concentrations . However , when used as refrigerant , there are several hazards associated with its use .

The main hazards of carbon dioxide are :

• Asphyxiation

• High pressures

• Rapid expansion of trapped liquid or gas

• Solidification – dry ice formation during ( instantaneous ) venting or discharge from safety valve

As mentioned , in small quantities CO2 is non-toxic , non-flammable and does not irritate skin or eyes and has no odour . However , at moderate to high concentrations it is dangerous being denser than air and can stratify displacing oxygen which will lead to asphyxiation .

The danger of R744 is to be estimated differently than that of halogenated refrigerants ( HCFCs and HFCs ) of the same safety group A1 . Carbon dioxide is dissolved in the blood , influences the respiratory centre in the brain and the oxygen absorption capacity of the red blood cells . Even at a carbon dioxide content of just a few percent in the air , respiration is accelerated and concentrations of 8 % or more are already life-threatening , even if there is still enough oxygen present .

HFC refrigerants generally have only a weak effect on the body . Concentrations from approximately 6 % have a narcotic effect . It usually only becomes life-threatening at approximately 20 % by volume due to oxygen displacement .

According to the standards ISO 817 , EN 378 and AHRI 700 , R744 is classified as A1 refrigerant . This means that it is non-flammable and of lower ( chronic ) toxicity .

The material data safety sheet ( MSDS ) includes all relevant information for the user of CO2 as refrigerant .

CO2 refrigerant bottles should generally be marked with the following information :

• Classification : Gas under pressure , liquefied gas

• Hazard statement : Contains gas under pressure , may explode if heated

• Storage : Protect from sunlight , store in a well-ventilated place

• CAS Number : 124-38-9

• Hazard class : 2.2 ( non-flammable , non-toxic gas )

For the provision with refrigerant CO2 , cylinder sizes from 13.4 to about 50kg charging amount are in use . For liquid and gas charging the cylinder is equipped with a dual port cylinder valve . Generally , cylinders are fitted with a residual pressure device ( RPD ) to ensure used refrigerant or any other substance cannot be reintroduced into a cylinder .

Riaan , with regards to safety equipment and measures , employers are obliged to protect their employees against any possible risk associated with the employee ’ s job performance . These include the provision of adequate and regularly serviced technical protection measures , such as installed gas sensors of the equipment , appropriate personal protective equipment ( PPE ) and organisational measures , such as supervision , coordination , rules of conduct , operating instructions , safety instruction , design of workplaces .

Emergency procedures must be established for the work with R744 . Each technician working on R744 systems must be trained so that they are capable of immediately following the relevant emergency procedures in case of an alarm .

The main safety equipment for the safe use of CO2 refrigerant are gas sensors , which have to be installed wherever large amounts of CO2 can escape in closed or sealed areas . The sensor gives an alarm if critical concentration is reached and warns people from entering the space or indicates that it has to be left immediately .

• Position gas sensors close to racks / storage shelves or evaporators as this is the most likely position of a leak and the resulting accumulation of refrigerant .

• Position gas sensor about 20 to 30 cm above floor level as CO2 is heavier than air and will accumulate close to the floor .

• Choose robust gas sensors with a self-test function . It is important that unauthorised people cannot change the settings .

Every machinery room where the leakage of CO2 can lead to a concentration exceeding the refrigerant concentration limit according to EN 378-1:2016 or local standards has to be equipped with an emergency mechanical ventilation system .

The system requires two independent controls and a gas sensor system . The ventilation can thereby be started from outside the room using an emergency switch or automatically based on the gas sensor readings . An additional emergency switch on the inside of the room is required .

Mechanical ventilation has to have a power supply that is independent of the refrigeration system . If a failure of the power system of the refrigeration system causes a leak , the ventilation will then still work . As CO2 is heavier than air , the system should be situated close to the floor .

The necessary volume flow of the ventilation is based on the charge size of the largest sized equipment in the machinery room . It is also possible to calculate an air exchange at the rate of 15 air changes per hour .

In case of a gas alarm :

• Leave the affected area immediately

• Inform people that are close by

• Ensure proper ventilation

• Enter the affected area only if the gas alarm is off and gas alarm system shows normal operation

In the case of someone needing to be rescued , only enter the area while using a self-contained breathing apparatus . As with other refrigeration systems , with the installation in a closed area it should be ensured that appropriate ventilation is provided to release the CO2 to the outside and to provide the required fresh air .

Riaan , I hope that this helps with your understanding around CO2 refrigerant and natural refrigerants in general . RACA