Processors, warehouses must retrofit valves in older ammonia refrigeration systems not up to code.
By Ekle Small and Durby Moore
Just as a new year reminds some that it’s time for a physical, food plant and cold storage warehouse operators may want to schedule a check-up for their ammonia refrigeration systems.
Although any ammonia refrigeration system runs the risk of a dangerous leak, older systems with aged or outdated piping are of particular concern. More specifically, anyone with an older system – or someone planning to update their piping – should carefully examine the system’s relief components.
Relief valve pipes and their corresponding venting systems are key to ammonia system safety. In refrigeration systems that use pressurized anhydrous ammonia, the relief valves and piping maintain safe pressure levels within the system piping and components. Without these critical relief systems, hazardous levels of pressure could cause ammonia (which is toxic under ambient conditions) to leak and lead to an explosion, danger to employees and product loss.
Consider the consequences
When the pressurized liquid ammonia found in these systems is released, it can aerosolize and become a dense gas. This gas can then travel along the ground, rather than rising into the air and dissipating. As a result, it can represent numerous hazards to human health, with effects of the chemical ranging from moderate irritation, to severe respiratory injuries, or even fatalities if released in high concentrations.
Authorities have not yet definitively linked an old pressure valve system failure to a catastrophic event involving an ammonia leak. However, accidental ammonia releases have been reported throughout the industry, and older systems can leave a facility exposed to the possibility of the dangerous consequences of a leak.
Ammonia leaks have led to death and injury to employees, emergency response personnel and people in surrounding communities. For example, a 1989 incident required the evacuation of nearly 6,500 residents in the town where the affected plant was located. Fifty residents received medical treatment as a result of the ammonia gas exposure.
These factors make it essential that facility management and engineers are aware of all applicable relief valve system codes, regulations and general precautions. Even if you use a third-party refrigeration facility, it is important to ensure that systems are up to code.
Codes and regulations
Two key regulations help ensure safety in the relief valve systems. In 2001, the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) changed refrigeration system regulations to increase safety and align codes with those in the chemical and petrochemical industries. While older equipment installed prior to 2001 is exempt from the new code, any new equipment or additions to older systems must comply.
The AHSRAE regulations - designed through a scientific approach - increased the size requirements of pipes in the relief valve venting system to accommodate pressure from multiple valve releases. In the event of an ammonia release from several valves at once, the new, larger pipes help prevent dangerous leaks by minimizing pressure in the relief headers. The older systems did not accommodate for the possibility of a simultaneous valve release, which could cause an increase in pressure within the relief header piping. The new systems, from a scientific and technical standpoint, provide additional safeguards to prevent a catastrophic event.
In addition, the International Institute of Ammonia Refrigeration (IIAR) requires the replacement of pressure relief valves every five years. Documentation should be made each time the valves are replaced, including stamping the replacement dates onto each unit to help ensure ongoing compliance.
Facility management also should be aware of regulations falling under the U.S. Department of Labor’s Occupational Safety and Health Administration (OSHA). Refrigeration systems are regulated through OSHA’s process safety management (PSM) regulations, which include detailed requirements and procedures for employers that use large amounts of hazardous chemicals, such as ammonia.
These stringent guidelines require employers to continuously and rigorously analyze, update and maintain each element of their processes to ensure worker safety. Failure to meet these regulations can result in severe fines. Each facility should have regular process analysis performed to (1) ensure compliance, (2) confirm that any danger or hazards have been identified and (3) document that the proper administrative and engineering controls are in place to deal with abnormal occurrences.
Engineers should conduct process hazard analysis (PHA) steps to ensure the system’s mechanical integrity and proper pipe thickness in the venting system. These services can be conducted through a PSM/PHA consultant.
Time to take action
Although leaks can occur in many areas of a cooling system, valves are particularly important. Retrofitting valves in an older system is not only a key step to protect employees and investments - it is a requirement for systems that are not up to code. The length of time required for retrofitting a new system can range from days to a few weeks, according to the size and intricacy of the system. Cost also varies according to these factors.
Even if codes and regulations do not require replacement, facility staff should be aware of any physical signs that the mechanical integrity of the relief valve and its piping system have been compromised.
Pipe pitting, flaking and rusting may be indicators of a problem and should be examined by an expert as soon as possible. Relief valve calculation studies are a common service and offer an in-depth analysis of the overall relief valve system. These studies often can help operators avert serious situations that may have otherwise been overlooked. Refrigeration systems also can incur failed insulation, rust and corrosion, and should be inspected regularly - even in newer systems - to avoid a costly or dangerous leak.
To ensure a safe and stable refrigeration system, facility operators should remain informed of relevant regulations and maintain a vigilant watch over facility equipment and procedures. For additional information on relief valve safety and applicable regulations, readers may visit the Web sites for OSHA (www.osha.gov), IIAR (www.iiar.org) and ASHRAE (www.ashrae.org).
Ekle Small is director of design in the refrigeration services division at Stellar, a Jacksonville, Fla., construction, design, engineering and mechanical services provider. Durby Moore is regional director for Stellar’s Atlantic Coast division. Readers may contact Small at email@example.com or 904-260-2900; and Moore, at firstname.lastname@example.org or 904-260-2900.