Refrigeration Plant Safety PDF

4th Class Edition 3 Part B Unit 9 Chapter 6 Refrigeration Plant Safety Learning Outcome When you complete this chapter you should be able to: Outline the potential hazards inherent to r...

4th Class Edition 3 Part B Unit 9 Chapter 6 Refrigeration Plant Safety Learning Outcome When you complete this chapter you should be able to: Outline the potential hazards inherent to refrigeration plants, the CSA requirements intended to mitigate hazards, and typical responses taken in the case of a significant leak. Learning Objectives Here is what you should be able to do when you complete each objective: 1. Identify and provide a basic explanation of the CSA B52 Code requirements for refrigeration plant machinery rooms. 2. Identify safe practices for refrigeration plant operation and maintenance. 3. Describe the appropriate emergency response to a significant refrigerant leak. 4. Describe the Canadian Environmental Emergency Regulations and how they relate to refrigeration plants. 6-1  Refrigeration Plant Safety Chapter 6 Chapter Introduction Jurisdictions enact legislation and develop regulations for the care and operation of large refrigeration plants, and place them under the authority of Power Engineers. This is because refrigeration plants pose various hazards to both workers and the public, such as: Pressure vessel or pressure piping explosion Combustion explosion Asphyxiation Cardiac arrest Chemical burns Freeze burns (frostbite) Chemical reactions This chapter covers the safety features found in refrigeration plants, as well as safe operation and maintenance practices. When refrigerant leaks occur, plant operators must be prepared to carry out a safe, effective, and environmentally responsible emergency response plan. For this reason, this chapter also addresses appropriate emergency response. 6-3 4th Class Edition 3 Part B  Unit B-9 Basic Concepts of Compression and Absorption Refrigeration Objective 1 Identify and provide a basic explanation of the CSA B52 Code requirements for refrigeration plant machinery rooms. While studying or reviewing this chapter, it will be helpful to refer to the PanGlobal CSA A E Academic Extract. Refrigeration Plant Safety Code Requirements All refrigeration systems are hazardous, but to varying degrees. The degree of hazard will depend upon: 1. The toxicity or flammability of the refrigerant fluid 2. The amount of refrigerant in the system 3. The building occupancy class 4. The leakage probability of the system 5. The internal pressure of the refrigeration system As plant operators or managers, it is important for Power Engineers to know the hazards related to a particular plant, its safety systems, and the function of the various safety systems that mitigate hazards, should an emergency situation arise. 1. Toxicity or Flammability of the Refrigerant Fluid Some refrigerants are, to various degrees, toxic. These include R-717 (ammonia) and R-123. R-717 is used in industrial refrigeration systems and in ice arenas. It is toxic in concentrations over 0.03% by volume in air. R-123 is used in large HVAC chillers. It is toxic in concentrations over 0.1% by volume in air. Some refrigerants are flammable and explosive. These include R-290 (propane) and R-717. CSA B52 considers R-290 to be more flammable and explosive than R-717. It has an explosive range between 2.1% and 9.5% in air. R-717 has an explosive range between 15% and 28% in air. R-717 leaks can be detected at extremely small concentrations in air, and are therefore likely to be stopped before concentrations reach the explosive range in air. Refrigerants that are neither toxic nor flammable are also dangerous. Many refrigerants are heavier than air. If a major leak occurs, dense refrigerant gas accumulates in low spots, and displaces air. In high enough concentrations, the refrigerant can asphyxiate individuals entering the low-lying space. Ammonia is lighter than air. It is therefore best to measure ammonia concentrations at various elevations should a leak occur. Often, refrigerants are changed to meet environmental regulations. This may result in a change in machinery room requirements. For example, R-123 chillers are often installed to replace R-11 chillers. R-11 is a Group A1 refrigerant. It has low toxicity, but is an ozone depleting substance. R-123 is safer for the environment, but is a toxic Group B1 refrigerant. R-11 chillers had no specific machinery room requirements; whereas R-123 chillers do, depending on the occupancy. Many buildings therefore must be retrofit with machinery rooms when replacement refrigerants are specified. 6-4 4th Class Edition 3 Part B  Refrigeration Plant Safety Chapter 6 2. Amount of Refrigerant in the System A refrigerant is only harmful at certain concentrations in air. For example, an ammonia concentration of 2 to 5 parts per million in air by volume creates a pungent odour. However, at this concentration, the atmosphere will not be explosive or toxic. R-134a, in a concentration of less than 5% in air, will not cause cardiac arrest. R-290, in a concentration of less than 0.53% in air, is not explosive. Therefore, refrigeration system designers consider the amount of refrigerant in the system and the volume of the enclosure that the refrigerant could leak into. Every effort is made to design systems that, if all the refrigerant leaks because of a catastrophic failure, the resulting concentrations will not be hazardous to those exposed. 3. Building Occupancy Class Buildings that house refrigeration systems serve a variety of purposes. Buildings are categorized according to their use, including: Residential Institutional Public Assembly Commercial Industrial Residential buildings have ordinary living spaces. Refrigerants leaks could have devastating effects in these buildings, especially if occurring at night when occupants are asleep. Institutional buildings present similar risks. In hospitals and penal institutions, hundreds of occupants may be housed or confined (i.e. not able to leave freely). Their ability to escape in the case of an emergency may be restricted due to medical reasons or incarceration. Public Assembly buildings, such as theaters, schools, and ice rinks, concentrate large numbers of people together, increasing their exposure risk and reducing their ability to escape. Commercial buildings include stores, malls, office buildings and restaurants. Many people gather in these locations, and have greater exposure risk if a catastrophic refrigerant leak should occur, again because of reduced ability to leave quickly. Industrial facilities include ice-making facilities, meat packing plants, cold storage facilities, and other processing facilities that use refrigeration systems. These plants can only be accessed by authorized personnel. Because of restricted access, the hazard to the public is lower in industrial facilities. 4. Leakage Probability of the System CSA B52 classifies refrigeration systems as having either a low or a high leak probability. These are defined as follows. High-Probability System A high-probability system is one where refrigerant-containing components are located in such a manner that refrigerant could leak into the occupied space. The leak may be due to a failed connection, seal, or pressurized component. The most common example of a high leak probability system is a direct expansion system. These use cooling coils directly fed with refrigerant. If a component should fail, refrigerant could enter the occupied space through HVAC ducting or other means. 6-5 4th Class Edition 3 Part B  Unit B-9 Basic Concepts of Compression and Absorption Refrigeration Low-Probability System This class includes indirect closed and double indirect systems. The most common examples are chilled water systems used in residential, commercial, public assembly, and institutional buildings. Chilled brine systems used in public assembly buildings are also indirect. Indirect systems have all refrigerant-containing joints, connections, and components effectively isolated from the classified area. For example, consider a commercial building cooled with chilled water. The refrigerant used to chill the water may be R-123, which is toxic. The refrigeration system components that contain R-123 must be confined to an isolated location. This will prevent refrigerant from leaking into parts of the building used for commercial purposes. 5. Internal Pressure of the Refrigeration System Refrigeration systems can be classified as low pressure or high pressure. The same pressure limitations apply to refrigeration plants. High pressure plants operate with a high-side pressure greater than 100 kPa. Low pressure plants have high-side pressures below 100 kPa. Many jurisdictions do not have mandatory operator requirements for low pressure refrigeration plants. These plants are less likely to develop devastating leaks or sustain catastrophic pressure component failure. Refrigeration System Design Rules Refrigeration systems are designed with varying degrees of safety, based on the above factors. Designers consider how much refrigerant can leak, how toxic or flammable the refrigerant is, how probable it is for refrigerant to leak into the classified space, and the type of occupancy. Then, features are added to eliminate or mitigate risks. These design rules are found in CSA B52 Code. Many Power Engineers work with ammonia refrigeration systems. These may be direct or indirect systems. The following applies to ammonia systems. Similar rules may apply to systems containing other refrigerants, depending on the combinations of the safety factors already discussed. Direct Systems Direct systems that use ammonia are only permitted in industrial occupancies. The safety considerations include the following: a) The area containing the refrigeration system machinery (eg. pumps and compressors) must be separated from the rest of the building by tight construction and tight-fitting doors. b) Access must be restricted to authorized personnel. c) Ammonia detectors must be installed in areas where refrigerant vapour from a leak will concentrate. The detector must provide a warning at a concentration of 300 ppm or less. d) No flame-producing device or hot surface above 425°C can be located in the vicinity where a leak could occur. e) All refrigerant-containing parts, except piping, low-side components, condensers, and parts outside the building, must be installed in a special machinery room. Systems over 75 kW (19 TR) must be installed in Class T machinery rooms, which have more stringent requirements. Indirect Systems Curling rinks and hockey arenas commonly use indirect brine systems, cooled with ammonia refrigerant. Unlike the direct system, there is no lessening of the system requirements for plants under 75 kW (19 TR) capacity. For indirect ammonia systems in public assembly, all refrigerant- containing parts, except piping, low-side components, condensers, and parts outside the building, must be installed in a Class T machinery room. 6-6 4th Class Edition 3 Part B  Refrigeration Plant Safety Chapter 6 Class T Machinery Rooms Practically every ammonia refrigeration plant operated by Power Engineers must be located in a Class T machinery room. Some of the requirements are as follows: Access Restriction Access to the machinery room shall be restricted to authorized personnel. Figure 1 shows a typical sign, placed on a machinery room door, used to restrict access. Figure 1 – Door Sign on Class T Machinery Room Doors Each machinery room must have a door or doors that open outward and are self-closing (and tight fitting if they open into the building). The doors must not open to a public corridor or any room used for assembly. The room must have at least one door that exits directly to the outside. Other exits that communicate with the building are permitted, but must go through a vestibule equipped with self-closing, tight-fitting fire doors. Figure 2 shows an exit door in a machinery room. Notice the “panic” bar on the door, operating certificates, and readily accessible fire extinguisher. These items meet the requirements of CSA B 52, jurisdictional licensing requirements, and building codes. Side Track Refrigeration plants, whether standalone or part of a larger facility, are subject to the requirements of codes such as the CSA B-52. However, they must also meet jurisdictional and local regulations which may control the building’s configuration and safety features. 6-7 4th Class Edition 3 Part B  Unit B-9 Basic Concepts of Compression and Absorption Refrigeration Figure 2 – Inside Door of Class T Machinery Room Openings and Penetrations There must be no openings that permit passage of escaping refrigerant to other parts of the building. All pipes piercing the interior walls, ceiling, or floor of a Class T machinery room must be tightly sealed where they pass through, and must not open into the machinery room. Open Flames and Hot Surfaces There must be no flame-producing device or hot surface over 427°C permanently installed in the room. Ventilation Machinery rooms must be ventilated to the outdoors. Most systems require mechanical ventilation, using one or more power-driven fans. Readily accessible fan switches must be installed inside and outside the machinery room. The fan switches outside the machinery room must be capable of starting the ventilation system, but not stopping it. 6-8 4th Class Edition 3 Part B  Refrigeration Plant Safety Chapter 6 Figure 3 shows views of opposite ends of a Class T machinery room. One end has a ventilation fan (left) and the other an exhaust damper (right). Figure 3 – Ventilation Fan and Exhaust Damper All locations must be equipped with a vapour detector that automatically starts the ventilation system, and actuates an alarm at ammonia concentrations of 300 ppm or less. The detectors must be located where the refrigerant from a leak has a maximum concentration (in the case of ammonia, multiple detectors may be required at different locations and elevations). Figure 4 shows an ammonia leak detector panel with a digital readout, alarm horn, and simple controls. Sensors in multiple locations feed signals to this control panel, which has contact closure outputs for local or remote alarms, alarm horns, alarm beacons, and the ventilation system. Figure 4 – Control Panel for Ammonia Leak Detection System 6-9 4th Class Edition 3 Part B  Unit B-9 Basic Concepts of Compression and Absorption Refrigeration Machinery Shutdown Switch A switch must be provided directly outside the machinery room, solely for shutting down the equipment in an emergency. Figure 5 shows the machinery shutdown switch (red plate), to the left of the ventilation system start switch, and below the alarm beacon. Figure 5 – Machinery Shutdown Switch, Ventilation Start Switch, and Alarm Beacon Power Engineers must know how to inspect, maintain, and repair the elements of Class T machinery rooms to ensure their own safety as well as that of the public. Most of these systems are easy to inspect and repair without specialized training. However, some systems may require the involvement of licensed tradespersons, including electricians, refrigeration mechanics, or instrumentation technicians. Table 1 has guidelines of routine inspection of Class T machinery rooms. 6-10 4th Class Edition 3 Part B  Refrigeration Plant Safety Chapter 6 Table 1 – Routine Class T Machinery Room Checks Item Check Repair Doors Door closer operates correctly Replace defective door closer Door weather-stripping is in good Replace damaged weather-stripping condition Repair or replace panic hardware Door panic hardware works Ventilation Test manual switch inside machinery Troubleshoot ventilation fan circuit system room Check for defective fan motor Test switch outside machinery room Check for defective damper drive Test fan startup using leak detection motor system Replace broken or frayed drive belts Check operation of air dampers Check ventilation fan drive belts Refrigeration Test according to manufacturer’s Calibrate refrigerant leak detector leak detector instructions Replace refrigerant leak detector head Check that alarm beacons flash as required Check that alarm horns activate Troubleshoot defective beacon or horn Check that the ventilation system Troubleshoot ventilation system starts or accelerates to high speed, according to the design Check other ventilation system components for correct operation Wall Check that all pipes or ducts that Seal wall penetrations with suitable penetrations pass through walls are properly material sealed Ducts Check that duct joints are well sealed Seal or re-seal the duct joints with proper duct sealant Signage Check that restricted access signage Install or replace signs is in place and suitably located Other Refrigeration Plant Safety Systems The CSA B52 Code requires numerous other pieces of equipment for safe refrigeration plant operation. These include safety limit controls, safety valves, stop valves, emergency discharge systems, piping systems, and operator instructions. Safety Limit Controls Like boilers, refrigeration systems have pressure vessels, pressure piping, and fittings with maximum allowable working pressures. For this reason, all ammonia compression refrigeration systems must have pressure-limiting devices (see Figure 6). These operate in a similar manner to the high pressure cut-offs of boilers. They are piped to sense the high-side pressure. When tripped, they shut off the compressors, and require manual reset. The CSA B52 code requires these controls to be set to not more than 90% of the system high-side design pressure. In most plants, this is also 90% of the high side safety valve setting. As with boilers, the pressure-limiting devices must be connected to the piping without any intervening stop valves that could render the device inoperative. This means that the high-pressure limit control must be connected to the compressor discharge pipe before the compressor discharge isolation valve. 6-11 4th Class Edition 3 Part B  Unit B-9 Basic Concepts of Compression and Absorption Refrigeration Figure 6 – Pressure Limiting Devices Safety Valves Safety valves are installed to protect the pressure vessels, pressure piping, and pressure-imposing elements (compressors). Compressor Protection Positive displacement compressors are capable of developing enough pressure to damage connected piping, vessels, and pipe fittings. These compressors can also develop enough pressure to rupture their own casings. To prevent this from occurring, every positive-displacement compressor with a discharge stop valve must be equipped with a pressure-relief valve. 6-12 4th Class Edition 3 Part B  Refrigeration Plant Safety Chapter 6 From an environmental and safety standpoint, refrigerant should only be discharged to the atmosphere as a last resort. Therefore, the safety valves installed on compressors usually discharge to the low-side of the system. In this case, pressure is relieved, and refrigerant is contained within the system. Figure 7 shows a safety valve installed on an ammonia compressor. Figure 7 – Compressor Safety Valve 6-13 4th Class Edition 3 Part B  Unit B-9 Basic Concepts of Compression and Absorption Refrigeration Vessel and Piping Protection Refrigeration system piping and vessels are designed to ASME codes. ASME BPVC VIII Division 1 requires pressure relief protection for pressure vessels. These vessels may include liquid receivers, chillers, condensers, and evaporators. Commonly, high side safety valves of ammonia refrigeration systems discharge into the low side, to reduce the likelihood of ammonia discharge to the atmosphere. For this to be acceptable, the low-side must have enough installed relief capacity for the entire refrigeration system. In this common situation, the high side safety valves will have reduced discharge capacity because of the backpressure exerted by the low side. Therefore, specially rated high side safety valves (ones that are not affected by backpressure) must be used. Figure 8 shows safety valves installed on a low side ammonia chiller. Figure 8 – Dual Safety Valves on a Chiller Note that two valves are mounted on a single fitting. The fitting is a three-way valve that places only one safety valve in service at a time. This allows one valve to be isolated so that it can be tested, recertified, serviced, or replaced. For this type of fitting to be used, each safety valve must meet the total relief capacity requirement. Never plug the vacant opening when a safety valve is removed from a dual safety valve setup. A spare safety valve - recently certified or in new condition, and of proper capacity and set point - must be on hand to install in the space created when valves are removed for servicing. The CSA B52 code also requires overpressure protection for lengths of piping that contain liquid refrigerant, and can be isolated. If a section of pipe is isolated and the temperature increases, hydrostatic liquid expansion may over pressurize the pipe and fittings, causing them to rupture. 6-14 4th Class Edition 3 Part B  Refrigeration Plant Safety Chapter 6 Stop Valves Refrigeration equipment requires regular servicing and occasionally repairs. This may involve removing or opening up system components. Best practice dictates that refrigerant should not be released to the atmosphere. Therefore, refrigeration systems must be designed so that individual components or piping can be isolated for servicing. In order to isolate system components, stop valves must be provided in the following locations: a) On each suction inlet of each compressor, liquid refrigerant pump, or condensing unit. b) On each discharge outlet of each compressor, liquid refrigerant pump, or condensing unit. c) On each inlet of each liquid receiver. d) On each outlet of each liquid receiver. e) On each inlet and outlet of condensers, when more than one condenser is used in parallel. Emergency Discharge Systems The CSA B52 has guidelines for rapidly discharging refrigerants into the atmosphere during a fire or other emergency. Though an optional part of the code, it is enforced by many Canadian jurisdictions. The emergency discharge system consists of a: a) A piping connection to the top of a liquid receiver or other vessel where liquid refrigerant is stored (see Figure 9). b) An emergency discharge valve, located outside of the building (see Figure 10). c) A diffuser, located at a high elevation, to spread the ammonia vapour over a large area (see Figure 11). Figure 9 – Emergency Discharge Line Connection on a Chiller 6-15 4th Class Edition 3 Part B  Unit B-9 Basic Concepts of Compression and Absorption Refrigeration The emergency discharge valve must be installed in a bright red glass-fronted box, located at least 2.3 m above the adjacent ground. This is so the valve cannot be operated by anyone other than the plant operator, a firefighter, or some other emergency personnel. The emergency discharge piping system can have no other valve installed in it. Beside the valve, there must be a power switch for shutting down the refrigeration plant in the case of an emergency. This is shown in Figure 10. Figure 10 – Emergency Discharge Valve and Equipment Shutdown Switch 6-16 4th Class Edition 3 Part B  Refrigeration Plant Safety Chapter 6 Though not a code requirement, in ammonia systems it is common practice for emergency discharge and safety valve piping to be painted bright red. In this way, it is easy to identify this piping when construction or renovation activities are taking place in the plant. Pressurized ammonia lines can thus be easily identified so they are not accidentally cut into or struck with mobile equipment. The diffuser pipe shown in Figure 11 is easily identified by its red colour. Figure 11 – Diffuser for Safety Relief and Emergency Discharge Safety Valve Discharge Piping Ammonia from safety valves can be discharged to the atmosphere through a diffuser (see Figure 11), or into a special water-filled tank. Water has a great affinity for ammonia. At 25°C, 100 grams of water can dissolve around 30 grams of ammonia. Therefore, it is possible for a large storage tank of water to absorb an entire ammonia refrigerant charge. CSA B52 code has instructions for determining the size of water tank needed to absorb the ammonia charge. One requirements is that the tank must be large enough to contain the water and ammonia without overflowing. Another stipulation is that the tank must be kept warm enough so that the water does not freeze. When refrigerant is discharged via a diffuser, its terminus must be a safe distance from doorways, operable windows, or mechanical air intakes. The CSA B52 code specifies the minimum distances from these openings. Operator Instructions For systems larger than 125 kW (32 TR), the owner of a refrigeration system must provide directions for operating the system, including precautions to be observed in case of breakdown or leakage. The instructions must be in a conspicuous location and as near as practicable to the compressor or compressors. 6-17 4th Class Edition 3 Part B  Unit B-9 Basic Concepts of Compression and Absorption Refrigeration As a minimum, the instructions must include: a) The telephone number of the first-response organization if an emergency situation arises. b) Instructions for shutting down the system in case of emergency. c) The name, address, and day and night telephone numbers of the service company under contract. d) The name, address, and telephone number of the nearest regulatory authority. e) Instructions for notifying the authority in case of emergency. It is also advisable to have an emergency evacuation plan prepared and readily available. Maintenance Requirements The CSA B-52 Code spells out some special maintenance that must be performed at regularly scheduled times. Safety Valves, Pressure Limiting Devices, and Other Controls Safety valves must be replaced every five years. Alternatively, they can be removed and recertified. The reason for this is that safety valves in refrigeration service do not have try levers. Simple try lever tests cannot (nor should they be) performed. Pressure limiting devices must be tested at least once every 12 months for set point accuracy and for their ability to properly stop the compressors. Other safety devices, such as low oil pressure cut-offs and high discharge temperature cut-offs, must be tested at least once every 12 months for set point accuracy and for their ability to properly stop the equipment. Leak Detectors Leak detectors must function at the specified refrigerant concentration. To verify this, they must be tested at least annually, in accordance with the manufacturer instructions. Detectors that fail the test must be immediately calibrated, repaired, or replaced. Equipment Specific Maintenance All safety related maintenance recommendations by the equipment manufacturer must be followed. This includes adjustments, repairs, calibration, and component replacement at the intervals specified by the manufacturer. Visual Inspection of the Plant CSA B52 requires visual inspection of refrigeration plant equipment, including quarterly inspection of all refrigeration lines, vent lines, outlets, and system components for: Vibration Corrosion Physical damage Blockage Insulation damage, including both piping and vessel insulation 6-18 4th Class Edition 3 Part B  Refrigeration Plant Safety Chapter 6 Leak Testing Testing for refrigerant leaks must be carried out periodically. The normal places where leaks occur are at: Valves Valve Stem Packing Threaded Connections Flanged Connections Flared Joints The location of a leak may be determined with: Moist red litmus paper Moist filter paper impregnated with phenolphthalein Sulfur candles Electronic refrigerant “sniffers” Chemical test papers change color in ammonia vapor. Sulfur candles form a white fog when in contact with ammonia. Condensers should be checked at all connections as well as throughout the coil. Air cooled condensers can sustain damage from weakened fan blades or damaged fan bearings. Water-cooled condensers should be checked for leaks by isolating the coolant, carefully cracking open a vent, and testing the atmosphere at the connection for escaped refrigerant. A similar process can be followed for an evaporator. Fan-coil evaporators and blast freezers can sustain damage from weakened fan blades or damaged fan bearings. Chillers should also be tested periodically, especially if the fluid is brine, which may be a factor in accelerated corrosion. Follow the manufacturer recommendations for testing. If no specific instruction is available, follow the water cooled condenser procedure. CAUTION NEVER take apart or crack open any piping connection on a refrigeration system, even if the connection is part of a chilled brine or water loop, without first testing for refrigerant at a vent. Treat all refrigerants with caution. DO NOT rely on the sense of smell. Many refrigerants are odourless and toxic, and many will displace atmospheric oxygen. Many refrigerants are heavier than air and will accumulate in low areas. Avoid low areas if there is a possibility of a leak. If the equipment is near floor level, test first before commencing work. Keep a refrigerant tester on at all times, and carry a calibrated personal oxygen monitor near your head. Ammonia is lighter than air, so keeping low is better for ammonia. Ammonia stinks, and is only slightly dangerous at first breath or taste. This is the warning to get out, get help, and get the proper PPE. Housekeeping Housekeeping is very important to permit safe and quick egress from a machinery room. Tripping over pails or mops while trying to get out of a dangerous situation makes matters worse. 6-19 4th Class Edition 3 Part B  Unit B-9 Basic Concepts of Compression and Absorption Refrigeration Objective 2 Identify safe practices for refrigeration plant operation and maintenance. Hazards of Ammonia Anhydrous ammonia is very corrosive, and exposure to it may result in chemical burns to skin, eyes, and lungs. This is because ammonia is hygroscopic and highly soluble in water. Human tissues, such as mucous membranes in nasal passageways and in the lungs, are inherently moist. Humans also excrete perspiration, saliva, and tears. Anything moist attracts and dissolves ammonia, forming highly corrosive ammonium hydroxide. Exposure to ammonia, then, will damage eye tissue, mucous membranes, and skin. If inhaled, it damages the lungs. When released to the atmosphere, ammonia dissolves readily in atmospheric moisture, forming a dense, caustic white cloud. NEVER enter a visible cloud of ammonia. It will cause serious lung damage! At atmospheric pressure, ammonia boils at about -33°C. It also has a very high latent heat of evaporation. Therefore, even a small amount sprayed on the skin or eyes can cause frostbite as well as chemical burns. Table 2 outlines of the potential effects of exposure to wide range of ammonia vapour concentrations. Table 2 – Potential Effects of Ammonia Exposure Concentration (ppm) Effects 2 normal odour threshold 5 to 50 headaches loss of the sense of smell nausea vomiting 70 tingling or burning in eyes, nose, or throat watering of the eyes sneezing coughing 70 to 300 irritation to the nose, mouth, and throat that becomes intolerable after a few minutes coughing and wheezing shortness of breath 300 to 500 immediately dangerous to life and health lung irritation/possible burning in lungs coughing fluid in the lungs (pulmonary edema) severe shortness of breath death Over 2000 fatal after a few breaths 6-20 4th Class Edition 3 Part B  Refrigeration Plant Safety Chapter 6 Those exposed to ammonia regularly (or repeatedly) may have a significantly reduced ability to detect ammonia by smell. Therefore, the nose should not be used to assess ammonia concentrations. Personal protective equipment should be used when there is a possibility of exposure above 50 ppm. Work Practices Disassembly Refrigeration systems require occasional repair and regular maintenance. Disassembly may be required for maintenance or to repair leaks. Before disassembling any part of a refrigeration system, ensure that all refrigerant, including vapour, is removed, and that the internal pressure is 0 kPa. Hot Work and Leak Checks Before hot work is performed on refrigerant lines, they must first be purged using inert gas to reduce combustion and toxicity hazards. When maintenance, system modifications, or leak repairs are complete, the system must be pressure tested to determine system integrity, according to CSA B52 code. If the system leaks, shut down the unit until it can be properly repaired. Refrigerant Storage Some facilities store refrigerant on site in compressed gas cylinders. Refrigerant cylinders must be stored a safe distance from an open flame or hot surfaces. They should be handled with care, because of the potential for frostbite due to escaping liquid refrigerant. Routine Maintenance Any routine maintenance activity that may create a discharge of refrigerant (such as adding compressor oil, draining oil pots, or manual purger operation), should be performed with the aid of a “buddy.” The buddy should have a water source readily available and a means for signaling for emergency assistance. If a serious ammonia leak occurs, the concentration of ammonia in air can be effectively reduced by spraying a water mist through the vapour. However, do NOT apply water directly to liquid ammonia since violent vapour production can occur. Oil Removal A great number of accidents occur when removing oil from oil pots. Ammonia compressors pump oil with the ammonia gas. Because oil and ammonia are non-miscible, the oil drops out in various parts of the piping system. Ammonia is less dense than lube oil, and floats above it. When oil accumulates in the bottom of evaporators and other low points in the system, it must be removed. This is done by attaching a flexible hose to a drain valve, placing the end of the hose in a bucket of water, and opening the valve slightly until no more oil is left in the oil pot. 6-21 4th Class Edition 3 Part B  Unit B-9 Basic Concepts of Compression and Absorption Refrigeration If the operator draining oil is overcome by fumes or must abandon his or her workstation due to an emergency, the drain could be left open causing a deadly release of refrigerant. Many jurisdictions require the installation of self-closing emergency stop valves (also called “dead man valves”) at all oil drain points in the system. This valve is manually opened against the force of a spring. When the handle is released, the valve springs shut. Figure 12 shows a dead man valve on an oil recovery pot at the base of a chiller. Note the guard valve situated closest to the pot. It is good practice to cap off the oil drain downstream of the dead man valve when oil is not being drained from the system. Figure 12 – Dead Man Valve for Draining Oil from a Refrigeration System Oil pots should be located where they are readily accessible. This not only helps operators drain oil, but it allows them to leave the area quickly if necessary. Operators should not be required to climb over pipes or equipment to access oil drain points. Some refrigerants cause refrigeration compressor oil to become acidic in the presence of moisture. Use PPE when handling used oil. Ammonia Pipe Labelling It is very important to know which plant pipes contain refrigerant. Often, refrigerant pipes run adjacent to other plant pipes, such as compressed air and potable water. Piping system modifications are common, as plants grow in capacity or reconfigure equipment. Cutting in to the wrong pipe during repairs or renovations can be hazardous or even catastrophic. Colour coding pipes helps to ensure the piping and instrumentation diagrams are up-to-date, reduces the chances of operator error, and significantly lowers the chances of accidentally damaging refrigeration piping. 6-22 4th Class Edition 3 Part B  Refrigeration Plant Safety Chapter 6 It has been common practice to paint emergency discharge and safety valve discharge piping bright red. However, in many plants, ammonia circulates through the entire facility in liquid or vapour form. Figure 13 shows a method of identifying plant ammonia piping, developed by the International Institute of Ammonia Refrigeration (IIAR). Side Track Piping should be consistently identified within a plant. Several pipe identification standards exist. Sometimes they are contradictory. It is important to know the plant pipe identification scheme and to apply it consistently. Ammonia piping labels, according the IIAR, must have the word “Ammonia” in black letters on an orange background. An arrow indicates the direction of refrigerant flow. The label also has several colour bands. One band shows the refrigerant state: A yellow colour band indicates liquid A blue colour band indicates vapour If the label has both colour bands, then liquid and vapour are both in the same pipe. Another colour band indicates whether the piping is high-side or low-side: A red colour band indicates high pressure A green colour band indicates low pressure Figure 13 – Ammonia Piping Label Valves should also be identified with a permanent tag that will not fade or fall off easily, denoting the valve number in the system, the fluid, and its state. 6-23 4th Class Edition 3 Part B  Unit B-9 Basic Concepts of Compression and Absorption Refrigeration Objective 3 Describe the appropriate emergency response to a significant refrigerant leak. Every plant layout is unique. Some plants have refrigerant-containing components confined to machinery rooms, accessible only to Power Engineers and service technicians. Cold storage and other industrial refrigeration facilities may have refrigerant-containing components located throughout the building, where a system leak can affect all warehouse staff. Some plants are in remote locations. Others are located in residential neighbourhoods. For these and other reasons, it is important to develop and follow site-specific procedures for emergency response. What follows, then, is a generalized response to significant refrigerant leaks. Personal Protective Equipment Employers must provide, and ensure that workers use, appropriate protective equipment to prevent repeated or prolonged skin contact with liquid refrigerants. Typical PPE includes impervious clothing, gloves, splash-proof safety goggles, and face shields. As well, employers must provide, and ensure that workers wear, appropriate respiratory protection. Where atmospheric conditions are immediately dangerous to life or health, such as during a leak, employers must provide workers with supplied-air respirators or escape-only respirators. Air-purifying respirators must not be used in IDLH atmospheres. Emergency Response Plan CSA B52 Code requires owners to provide employees with a written emergency response plan. This may be in addition to an Environmental Emergency (E2) response plan. The plan must include an explanation of worker roles, lines of authority, necessary training, communication protocols, and PPE requirements. Action in the Event of a Significant Leak It is imperative to follow the emergency response plan for the plant, in the event of a significant refrigerant leak. The following information is general, and encompasses the types of action to take. If a refrigerant leak occurs and there is no way to immediately identify the potential for workers or facility occupants to be exposed to respiratory hazard, the leak must be considered IDLH, and the appropriate emergency response taken. Properly functioning and calibrated refrigerant leak detectors should activate alarms and beacons to alert plant operators and facility occupants. As well, mechanical ventilation should start automatically and operate at maximum capacity. Prior to entering the machinery room, as an additional precaution, manually activate the mechanical ventilation system. Stop the refrigeration machinery. Ventilation and machinery shut-down can be done without entering the machinery room, using the switches outside the room. Allow the mechanical ventilation to bring refrigerant concentrations to within the Permissible Exposure Limit (PEL) for the specific refrigerant. According to OSHA, the PEL for ammonia is a time-weighted average of 50 ppm. If concentrations remain above an acceptable level, proper respiratory protection and other PPE must be donned before entering the machinery room. 6-24 4th Class Edition 3 Part B  Refrigeration Plant Safety Chapter 6 Human safety is the first consideration when a leak occurs. It is better to permit a leak to continue than to endanger the lives of occupants. Individuals that are not required to address the emergency must be evacuated from the premises, and mustered to a safe location. Call emergency services. Cordon off the area surrounding the leak, and let no one enter the area until the emergency is over and airborne refrigerant concentrations are safe. Any decision to vent refrigerant through an emergency discharge system should be made by, or at the advice of, trained emergency services personnel. Such as decision could impact the air quality over a large geographic area, and may involve the evacuation of nearby neighbourhoods. In this case, more emergency responders will likely be required. Persons trapped in an ammonia leak should breathe as little as possible and open their eyes only when necessary. Some protection is possible by holding a wet cloth over the nose and mouth. A trapped person should remain close to the floor, since ammonia vapour rises. Then, proceed to the source of ventilation air by travelling against the airflow. First Aid First aid certification courses are general in nature; they do not cover the specific treatment of refrigerant exposure. Here, then, are some guidelines for administering first aid to those exposed to ammonia liquid or vapour. Keep in mind that the following measures are not comprehensive, and are no substitute for expert medical attention. Always secure emergency medical treatment for individuals burned or overcome by ammonia prior to administering first aid. CAUTION First aid should only be administered by individuals who are trained and certified. Prior to administering first aid, ensure the victim is in a safe location, and secure the assistance of emergency medical services. Persons exposed to ammonia should be removed to a warm, fume-free location, and placed in a reclining position with head and shoulders elevated. Keep the victim warm with blankets. Skin Contact If liquid ammonia contacts a person’s skin, the victim should be immediately brought to a safety shower and the affected area flooded with water for at least 15 minutes. If no safety shower is available, the affected body parts should be immersed in relatively warm water. The victim’s clothing may be frozen to the skin. Once the clothing is thawed, remove it so that water can irrigate the skin directly. Then, continue flooding the skin for an additional 15 minutes. Do not apply ointments or cover burns with dressing. Instead, merely cover the affected area with a clean cloth, to provide protection until medical care arrives. If ammonia entered the nose or throat but the victim can still swallow, have them drink large quantities of water. Never give anything by mouth to an unconscious person. Eye Contact Speed is essential to prevent blindness. Immediately take the victim to the nearest eyewash station. If an eyewash station is not nearby, any clean water source can be used. The eyes must be irrigated with generous amounts of clean water for at least 30 minutes. During this time, the eyelids must be held open. The victim must receive prompt medical attention from a physician. Those working with or near ammonia refrigeration systems may be accidentally exposed to ammonia. For this reason, workers in refrigeration plants should not wear contact lenses. 6-25 4th Class Edition 3 Part B  Unit B-9 Basic Concepts of Compression and Absorption Refrigeration Inhalation A conscious person who has inhaled ammonia should be taken to an uncontaminated area with copious amounts of fresh air. If overcome by ammonia, the victim should be immediately carried to a safe, location and given artificial respiration, if necessary. If the victim is breathing, oxygen may be administered. Site Specific Training To be effective emergency responders, Power Engineers that work with refrigerants and refrigeration plants must be well trained in site specific procedures. This training is in addition to the training already received as part of the Power Engineer training. Site specific training usually includes: a) Properties of the refrigerant in use b) Toxicity and flammability c) Safe handling procedures d) Emergency procedures, addressing fires, spills, accidental releases, and evacuation e) Written safe work procedures f) Use of PPE, including respiratory protection g) Working alone (even entering a machinery room may be considered working alone) h) Testing and verifying leak detection equipment i) First aid j) Maintenance procedures, such as: Draining oil Adding oil to the compressors Manually purging non-condensable gases Isolating areas or parts of the system Pumping down parts of the system 6-26 4th Class Edition 3 Part B  Refrigeration Plant Safety Chapter 6 Objective 4 Describe the Canadian Environmental Emergency Regulations and how they relate to refrigeration plants. Canadian Environmental Protection Act (CEPA) The Canadian Environmental Protection Act (CEPA) is “an act respecting pollution prevention and the protection of the environment and human health in order to contribute to sustainable development.” According to Section 193 of CEPA 1999, an environmental emergency is: a) an uncontrolled, unplanned or accidental release, or release in contravention of regulations, of a substance into the environment; or b) the reasonable likelihood of such a release into the environment. Environmental Emergency (E2) Regulations The Environmental Emergency (E2) Regulations came into force under the authority of the CEPA in 2003. The intention of the regulations are to protect the environment and human life, by preventing, preparing for, responding to, and recovering from environmental emergencies. Under E2 Regulations, any person who owns or has the charge, management, or control of a listed substance on a fixed facility may be required to: a) Identify the listed substance and where it is located b) Prepare an environmental emergency plan c) Implement, update, and test the plan annually d) Provide notice of closure or decommissioning e) Report environmental emergencies involving regulated substances Note that in regulated refrigeration plants, Power Engineers are the ones who have charge of, manage, or control these hazardous substances. Environmental Safety of Refrigerants There are currently 215 substances listed under the E2 Regulations, including anhydrous ammonia. Ammonia refrigeration plants require an E2 plan if the total amount of refrigerant on site equals 4.5 tonnes or more. For perspective, single sheet ice arenas have refrigerant charges around 300 kg. Therefore, it can be seen that the E2 regulations only apply to very large ammonia refrigeration plants. 6-27 4th Class Edition 3 Part B  Unit B-9 Basic Concepts of Compression and Absorption Refrigeration Environmental emergency plans must: a) Identify any environmental emergency that may occur at the facility in question and the harm or danger it may cause. b) Describe the measures for preventing, preparing for, responding to, and recovering from any environmental emergency. c) List the individuals who carry out the plan when an environmental emergency happens, and describe their roles and responsibilities. d) Identify the training required for each of those individuals. e) List the emergency response equipment included as part of the E2 plan, and the equipment location. f) List how members of the public affected will be notified of the emergency, and kept informed of the emergency measures being taken. Every environmental emergency plan must: Be site-specific Address the full range of hazards present on the site Include site plots and material safety data sheets (MSDSs) for each regulated substance Maintain records of annual testing Be updated annually Be verified annually with a test Include site-specific training Employers should develop accidental release scenarios based on an environmental emergency that may occur. The scenario should focus primarily on a worst-case involving the largest possible substance release. Alternative scenarios involving the release of lesser amounts of substance should also be developed. The ultimate responsibility for E2 compliance falls on the owner of the plant. It is their responsibility to develop and seek approval of the E2 plan. Shift employees, though, are responsible for carrying out the plan, including the development of scenarios, the validation of the plan, the emergency responses, the documentation of tests and events, and the communications mandated by the regulations. 6-28 4th Class Edition 3 Part B  Refrigeration Plant Safety Chapter 6 Chapter Summary Jurisdictions legislate the care and operation of large refrigeration plants, and place them under the authority of properly trained, certified, and qualified Power Engineers. This is because refrigeration plants pose many hazards to both workers and the public. This chapter covered the safety features found in refrigeration plants, as well as safe operation and maintenance practices. Plant operators must be prepared to carry out safe, effective, and environmentally responsible emergency response plans. Further site-specific training on equipment operation, isolation, shutdown, and emergency plans, as well as first aid training, are critical elements that enable Power Engineers in their effective emergency response. 6-29 4th Class Edition 3 Part B  Unit B-9 Basic Concepts of Compression and Absorption Refrigeration 6-30 4th Class Edition 3 Part B  Refrigeration Plant Safety Chapter 6 Knowledge Exercises – Chapter 6 Name: _____________________________ Date: _______________________________ Instructor: __________________________ Course: _____________________________ Objective 1 1. What determines the degree of hazard of a refrigeration system? 2. Compare the toxicity of R-123 and R-717. 3. Compare the risk faced by occupants of public assembly buildings to the occupants of industrial buildings, if an ammonia leak should occur. 4. What are high leak probability and low leak probability refrigeration systems? 5. What is the maximum alarm set point for an ammonia vapour detector? 6-31 4th Class Edition 3 Part B  Unit B-9 Basic Concepts of Compression and Absorption Refrigeration Chapter 6 (Cont.) 6. Identify 7 potential hazards in refrigeration plants. 7. If an ammonia leak detector identifies that the ammonia concentration in a certain area is 3 PPM, will the alarm go off? Why? 8. Why must extra precautions be taken when assessing the refrigeration safety needs of occupants in institutional buildings? Objective 2 9. What is a “dead man valve”? Where are they found? What purpose do they serve? 10. Why should a maintenance “buddy” have ready access to water? 6-32 4th Class Edition 3 Part B  Refrigeration Plant Safety Chapter 6 Chapter 6 (Cont.) 11. An ammonia pipeline contains high pressure liquid. What are the labelling requirements according to IIAR? Objective 3 12. What are the typical PPE provisions in a refrigeration plant? 13. What should a person do if trapped by an ammonia leak? 14. What first aid should be given to a person who gets ammonia sprayed on their skin or clothing? 15. List five examples of maintenance procedures for which a refrigeration plant engineer must receive site-specific training. 6-33 4th Class Edition 3 Part B  Unit B-9 Basic Concepts of Compression and Absorption Refrigeration Chapter 6 (Cont.) Objective 4 16. What is the Canadian Environmental Protection Act? 17. According to CEPA, what is an environmental emergency? 18. What is the purpose of the Environmental Emergency (E2) Regulations under the CEPA? 6-34 4th Class Edition 3 Part B