By Phil Boudreau
As discussed in Part I in Mechanical Business Jan/Feb 2023, workplace accidents are frequently the result of taking shortcuts and/or using tools incorrectly and/or ignoring safety controls. The following are additional safety considerations when working in the field
Hot and cold surfaces
The surface temperatures of refrigeration systems can be well below 0˚C (32˚F). Conversely, surface temperatures may exceed 60˚C (140˚F). Extreme temperatures can result in burns to the skin. Always wear long pants, long-sleeve shirts, and gloves that will provide adequate protection for the skin. The edges of steel framework, sheet metal, coil fins, and so on, can be quite sharp in some cases. Always wear a good pair of protective gloves when working with system components such as these. For information on choosing protective gloves, search
The right glove for the job at mechanicalbusiness.com.
Charging manifold and hoses
It is best practice to use the shortest hoses possible. Preventing refrigerant release as much as possible is always an important consideration but, from a safety point of view, refrigerant release can result in severe burns to skin and tissue.
Table 1 lists some examples of refrigerants along with their boiling temperatures at 14.7 psia.
Liquid R744 will become solid, dry ice when released to the atmosphere at a pressure level of 14.7 psia. At this pressure, the temperature of the dry ice, which sublimes directly to a vapour, is -109.2˚F. Many materials become brittle at very low temperatures such as this. As a result, system components and/or piping may become compromised when exposed to such low temperatures.
Whenever working with refrigerants, wear the appropriate PPE, including a good pair of protective gloves and safety glasses. Ensure that gauges and hoses are well-maintained and kept in safe working order. Hoses that are split or cut must not be used and must be replaced. Damaged gauges must be replaced also.
Tools and equipment
Tools used in mechanical work should be well maintained. Broken components should be replaced. Use an authorized repair centre to make the repairs. Never use equipment such as a recovery machine or vacuum pump that has a damaged or frayed power cord. Also, it is very important that tools such as this are properly grounded. If an extension cord is used, ensure it has a ground pin and is connected to a grounded outlet.
Electrical test instruments
Invest in your electrical test instruments wisely. Ensure multimeters and clamp-on ammeters and other instruments are of very good quality and conform to the latest safety standards and carry local approvals such as CSA. For measuring voltage, an instrument that meets at least CAT III for high voltage (600V) is recommended, but CAT IV is even better. Test leads must be replaced from time to time as they tend to degrade over time. When making high-voltage measurements, protect yourself using the approved personal protection equipment or PPE.
Starting compressors safely
Take the time to ensure that pressure controls are set to ensure that the compressor can only operate within its intended envelope and that both the suction and discharge service valves are open. Make sure the pressure controls are connected to the correct port locations on the compressor. This is especially important and required in the case with the high-pressure switch. If the high-pressure switch is installed downstream of the compressor’s discharge service valve it will not be able to protect the compressor from over-pressure. This can of course, result in a very dangerous situation. R744 (CO2) transcritical compressors typically have a pressure relief valve installed on the compressor just before the discharge service valve. In the event that the compressor started up with the service valve closed, it is very likely the pressure relief valve will open. This results in a secondary concern, which is the potential venting of a good portion of the R744 from the system. Leave the mechanical room immediately if this situation occurs. Do not re-enter the room without wearing an approved respirator or wait for the R744 concentration level to return to safe levels.
Contaminated oils
Compressor lubricants can become very acidic due to chemical reactions that sometimes take place within the system. Always be cautious when handling these lubricants and wear protective gloves and protective glasses. The oil should be treated as hazardous waste and disposed of using a company that provides services for disposing of hazardous chemicals and oils.
Never bypass pressure controls
Bypassing a high-pressure control can lead to a dangerous situation, especially when the system is left unsupervised. High-pressure controls must never be bypassed under any circumstances. They are required to prevent the compressor from operating outside of its intended envelope. The next layer of safety after the high-pressure switch are the pressure relief valves on the compressors and the system.
Drive belts, pulleys and couplings
After working with belts and pulleys (that is adjusting drive belts and so on), be sure to re-install all protective guards. Moving belts and pulleys can present a very dangerous situation resulting in serious injuries or even death when these components are left exposed. Compressors driven directly by means of a coupling generally have a protective screen or mesh that covers the access areas to the coupling. Again, always ensure these protective guards are re-installed after performing service to the equipment.
Variable speed drives
Variable speed drives convert voltage from the AC input mains and convert them to DC voltage and store this in a capacitor bank. When a VFD is powered down, the capacitors will continue to hold a charge. This charge will bleed over time. An indicator light on the front panel of the VFD will be lit while there is a charge present. Never attempt to open a VFD before ensuring the charge has dissipated.