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Basis of Safety (BOSS): Equipment Risk/Exposure
Equipment risk and exposure are critical considerations in process safety management, particularly when implementing Basis of Safety (BOSS) principles. In industrial settings, various systems and equipment pose unique challenges and potential hazards that must be carefully assessed and mitigated. Understanding these risks is essential for maintaining safe operations and preventing incidents that could lead to equipment damage, production losses, environmental impacts, or personnel injuries.
Building on our previous blog post that introduced the Basis of Safety (BOSS) framework, this second installment reaches deeper into the specific risks associated with various types of equipment. This post will cover specific risks associated with piping systems, pumps, tanks, and dust-handling equipment, along with effective BOSS strategies for mitigating these hazards.
Here’s what you’ll discover in this article:
In the following sections, we’ll explore specific examples of equipment risk and exposure, along with corresponding BOSS mitigation approaches for different systems commonly found in industrial settings.
Piping Systems
Piping in Flammable Liquid or Combustible Dust Service
When dealing with piping systems that handle flammable liquids or combustible dust, the primary consequence is the risk of a fire. Such a fire can have severe implications, ranging from permanent disability to fatality.
The potential severity underscores the critical need for rigorous safety measures. Fires in these contexts can result from various sources, including equipment failure or accidental ignition, and their impact can be devastating not only to individuals but also to the overall safety and integrity of the facility.
Basis of Safety:
Eliminate Fuel – Containment:
- Employ accepted engineering design practices.
- Adhere to ASME B31 Code: ASME B31.4 for Liquid Transportation Systems.
- Select piping with ANSI flange ratings above the deadheaded pump pressure.
- Use spiral wound metal gaskets or Teflon gaskets, keeping in mind potential deformation during a fire.
Eliminate Ignition Sources:
- Implement proper grounding and bonding.
- Design zoned areas according to Class 1, Div 1 (Zone 0 or 1) and Class 1, Div 2 (Zone 2) classifications.
- Use Electrostatic Discharge (ESD) shoes or bonding straps.
- Ensure all equipment is electrically classified.
- Insulate hot surfaces.
Mitigation Measures:
- Install drains to limit surface area.
- Use Lower Explosive Limit (LEL) monitors.
- Implement ventilation systems with at least 6 air exchanges per hour and local ventilation with adequate capture velocity.
- Install an Aqueous Film-Forming Foam (AFFF) fire protection system.
Pumps
Pump Seal Failure
When a pump seal fails, the primary consequence is the loss of containment of flammable liquids, which can lead to severe outcomes such as a fire or permanent disability. The failure of a seal can result in flammable liquids escaping from the pump, increasing the risk of fire or hazardous incidents due to the presence of uncontained flammable material. This situation necessitates stringent safety measures to prevent such failures and to mitigate their potential impacts.
Basis of Safety:
Eliminate Fuel – Containment:
- Use a double mechanical seal pump if the discharge pressure is too low for a seal-less magnetic drive.
- Ensure the outer seal water pressure is set higher than the inner seal’s flammable liquid pressure.
- Install a seal pot to contain any leakage.
- Implement a low pump seal water pressure alarm to detect potential issues early.
- Consider using seal-less magnetic drive pumps as an alternative to traditional seals.
Design Considerations:
- Design pump systems to minimize the probability of deadheading by incorporating features to prevent pump blockage.
- Fit systems with spill-back loops to manage excess pressure and prevent containment loss.
- Include high-temperature switches to avoid overheating and subsequent seal failure.
Mitigation:
- Apply flange wraps or shielding to provide an additional layer of protection against leakage and potential fires.
Pump Overpressure
Overpressure in pumps, which can occur due to seal failure or deadheading, poses a significant risk. When a pump is deadheaded, with the downstream valve closed, the discharge pressure may exceed the Maximum Allowable Working Pressure (MAWP) of the pump casing or downstream piping. This can lead to the expulsion of shrapnel, causing potential injury to personnel. Additionally, if the liquid involved is flammable, the loss of containment can result in a pool fire. Such scenarios can result in severe injuries or fatalities.
Basis of Safety:
Eliminate Fuel/Energy – Containment:
- Install pressure relief valves (PSVs) on positive displacement pumps that relieve pressure back to the suction side.
- Design and select centrifugal pumps to ensure that the ANSI rating of the pump casing, flange, and piping is not exceeded, even if the pump is deadheaded.
- Use a high-pressure switch on the pump discharge with an interlock to shut down the pump if overpressure is detected.
- Implement a low-flow switch on the pump discharge with an interlock to shut down the pump if flow is insufficient
Pump Explosion – Any Material
Explosions can occur with any material, including water, if confined within a pump. When both suction and discharge valves are closed, the frictional forces can heat the material to its boiling point, leading to a significant pressure build-up and potential explosion. Such explosions pose a serious risk of permanent disability or fatality due to the expulsion of shrapnel and high-pressure impacts.
Basis of Safety:
Containment:
- Use interlocks to shut down the pump in case of high pressure, low flow, or potentially high temperature, including:
- A high-pressure switch on the pump discharge.
- A low-flow interlock.
- A high-temperature interlock, although it may not always activate promptly.
Mitigation:
- Install a pressure relief valve on the pump discharge, vented to a safe location to manage excess pressure and prevent explosions.
Tanks
Tanks in Flammable Liquid Services
Tanks containing flammable liquids present significant risks of fire or explosion due to both internal and external ignition sources. Internal ignition sources, such as static discharge, and external sources, like lightning, can trigger severe incidents if not properly managed. The potential for fire or explosion highlights the need for comprehensive safety strategies to mitigate these risks and protect both personnel and property.
Basis of Safety:
Eliminate Oxygen:
- Use nitrogen inertion or install a floating roof tank to reduce the presence of oxygen and minimize the risk of ignition.
Eliminate Ignition Sources:
- Internal Ignition:
- Implement bonding and grounding practices.
- Avoid splash filling to prevent static discharge.
- External Ignition:
- Install lightning rods to protect against lightning strikes.
- Use flame arresters to prevent flames from entering the tank.
- Ensure areas are classified according to electrical safety standards.
Mitigation:
- Construct dikes around the tank to contain any potential spills.
- Apply AFFF (Aqueous Film-Forming Foam) both inside and outside the tank, with automatic activation for enhanced fire suppression.
- Maintain proper layout and spacing of tanks to prevent chain reactions.
- Install fire walls outside of dikes to limit thermal radiation and provide time for personnel evacuation.
Tank – Overfilling
Overfilling a tank can lead to severe outcomes, including loss of containment, environmental damage, and significant financial loss. Such incidents often occur during truck unloading or material transfers into the tank. The risks extend beyond injury, particularly with hazardous materials like acids or caustics, to include environmental harm and substantial monetary losses.
Basis of Safety:
Containment:
- Install a high-high level switch (LSHH) to trigger interlocks that stop the unloading pump when the level exceeds safe limits.
- Mitigation:
- Ensure secondary containment systems are adequately sized to capture any overflow material.
- Require appropriate PPE for personnel involved in unloading or transfer operations.
- Design the tank layout and spacing to keep material contained within the diked area.
Tank – Overpressure
Overpressure in tanks can lead to structural failure, often along seams or corroded areas, resulting in significant consequences such as permanent disability or financial loss. Effective containment systems are essential to manage the pressure and prevent tank rupture. Weak seam roofs and properly sized pressure-vacuum vents are crucial to accommodate thermal expansion and ensure safety.
Basis of Safety:
Containment:
- Implement a weak seam roof that splits to release pressure safely and prevent tank rupture.
- Install pressure-vacuum (PV) vents to manage pressure fluctuations.
- Use emergency vents to provide additional relief in case of unexpected overpressure.
Mitigation:
- Provide secondary containment that is adequate to capture material in case of tank rupture.
- Ensure PPE is available for personnel working in or around the tank area.
- Design layout and spacing to ensure that material remains contained within the diked area.
Tanks – Under Vacuum
Basis of Safety:
Prevention:
- Ensure that vacuum vents are adequately sized and designated as safety-critical, with thorough preventive maintenance (PM) procedures in place.
Mitigation:
- Implement containment dikes to manage any potential leaks and prevent environmental or property damage.
Distillation Columns & Reflux Drums – Loss of Containment
Loss of containment in distillation columns or reflux drums can lead to significant risks such as pool fires or vapor cloud explosions. These incidents can have severe outcomes, potentially resulting in single or multiple fatalities. The risk is elevated by the presence of high-pressure and flammable materials, making it crucial to implement comprehensive safety measures to manage pressure relief and prevent ignition sources.
Basis of Safety:
Containment – Eliminate Fuel:
- Ensure the vessel maintains its Maximum Allowable Working Pressure (MAWP).
- Install a high-pressure transmitter at the bottom of the column, connected to the Basic Process Control System (BPCS) with a high-pressure alarm.
- Use a high-pressure switch at the bottom of the column linked to the Safety PLC to close steam and alcohol valves when pressure exceeds the Pressure Safety Valve (PSV) relief pressure.
- Install a high-pressure switch at the top of the column connected to the BPCS to close steam and alcohol valves.
- Use a high-level switch in the reflux drum linked to the Safety PLC to shut the steam and alcohol feed valves to the column.
- Select appropriate metallurgy to prevent corrosion damage.
Eliminate Ignition Sources:
- Ensure proper bonding and grounding, including the use of spiral wound gaskets.
- Maintain zoned areas and use electrically classified equipment.
- Provide Emergency Shutdown (ESD) shoes for personnel.
Mitigation:
- Utilize pressure safety valves vented to safe locations to manage excess pressure.
Combustible Dust Handling Equipment
Dryers
Dryers handling combustible dust face significant risks, including fire or explosion, which can result in fatalities. These risks arise from internal ignition sources that can ignite dust clouds, necessitating stringent safety measures to eliminate ignition sources and control dust concentration.
Basis of Safety:
Containment – Eliminate Fuel:
- Use nitrogen inerting or dilution to maintain the dust concentration below the Minimum Explosive Concentration (MEC). While nitrogen inerting can be costly, it remains an effective measure.
Eliminate Ignition Sources:
- Keep temperatures below the Thermal Onset Temperature.
- For new projects, use ATEX-rated equipment.
- For existing equipment, perform a Mechanical Equipment Ignition Risk Assessment (MEIRA).
- Ensure proper bonding and grounding for operators and equipment.
Mitigation:
- Implement explosion suppression systems or venting; note that explosion venting is generally unsuitable for rotary dryers.
- For vacuum dryers, operate at a vacuum level that keeps explosion pressure below the Maximum Allowable Working Pressure (MAWP) of the vessel.
Cyclones
Cyclones, generally low-risk due to their design, can still present hazards if not properly managed. They operate below MEC, but potential ignition sources from upstream equipment must be addressed to prevent explosion propagation.
Basis of Safety:
Prevention of Ignition Sources:
- Ensure upstream equipment does not introduce ignition sources.
Mitigation:
- Install an 8-blade rotary valve at the cyclone’s base to serve as explosion isolation and for product discharge.
Mills
Mills can pose significant risks of fire or explosion, potentially leading to fatalities. Effective safety measures are essential to prevent ignition sources, eliminate fuel, and manage potential explosions.
Basis of Safety:
Eliminate Ignition Sources:
- Use rare earth magnets and metal detectors with kick-out features to remove metallic contaminants.
- Install spark detectors with interlocks to shut down airflow in case of sparks.
Eliminate Fuel:
- Employ inerting and dilution methods to keep material below the Minimum Explosive Concentration (MEC).
Mitigation:
- Implement explosion pressure or shock-resistant construction to withstand Pred or Pmax.
- Use explosion venting systems.
- Install upstream and downstream isolation valves to prevent explosion propagation.
- Monitor temperature at the mill outlet and hopper to detect potential blockages.
- Include temperature monitoring inside the mill with interlocks to shut down operations if overheating occurs.
Baghouses
Baghouses, essential for handling particulate matter, present risks of fire or explosion, potentially resulting in fatalities. Effective safety measures must focus on both prevention and mitigation to manage these risks.
Basis of Safety:
Eliminate Ignition Sources:
- Prevent ignition sources from upstream equipment.
- Use bonding and grounding, especially for bags which can present static ignition sources.
Eliminate Fuel:
- Implement dilution to maintain the dust concentration below the Minimum Explosive Concentration (MEC).
Mitigation:
- Install explosion panels with proximity switches.
- Use isolation valves at the baghouse inlet to protect upstream equipment, closing when proximity switches are activated.
- Employ 8-vane rotary valves for isolation to protect downstream equipment.
- Implement fire suppression systems using water, nitrogen, or carbon dioxide, activated by high temperature, rate of change, or pressure.
- Install temperature switches inside the baghouse to detect fires.
- Use temperature alarms at the baghouse exit for early warnings of potential fires.
Effectively managing equipment risk and exposure is crucial to a robust safety culture in industrial settings. By leveraging the Basis of Safety (BOSS) principles discussed in this and the previous blog, organizations can systematically identify, assess, and mitigate risks associated with their equipment. You can read our first blog post, “Basis of Safety: A Comprehensive Approach ,” here to learn more about the comprehensive basis of safety.
