April 26, 2011
Pilots and Process Safety
I am talking about Flare Pilots! Do not underestimate the need for keeping your flare systems and pilots, including their ignition systems in good condition. A working flare is a silent sentinel for process safety. For a troubleshooting guide on flare systems see this link.
April 24, 2011
Lessons from Deepwater Horzon incident investigation by USCG
The US Coast Guard has released its investigation report on the Deepwater Horizon disaster. There are lessons to be learnt for us in the chemical processing industry. The key findings from the report are given below:
"Failure to Use the Diverter Line: When the drilling crew directed the uncontrolled well flow through the Mud Gas Separator (MGS), the high pressure exceeded the system’s capabilities and caused gas to discharge on the Main Deck. Alternatively, the crew could have directed the well flow through a “diverter line” designed to send the flow over the side of the MODU (Mobile Offshore Drilling Unit). Although the diverter line also may have failed under the pressure, had it been used to direct the flow overboard, the majority of the flammable gas cloud may have formed away from the Drill Floor and the MODU, reducing the risk of an onboard explosion.
Hazardous Electrical Equipment: At the time of the explosions, the electrical equipment installed in the “hazardous” areas of the MODU (where flammable gases may be present) may not have been capable of preventing the ignition of flammable gas. Although DEEPWATER HORIZON was built to comply with IMO MODU Code standards under which such electrical equipment is required to have safeguards against possible ignition, an April 2010 audit found that DEEPWATER HORIZON lacked systems to properly track its hazardous electrical equipment, that some such equipment on board was in “bad condition” and “severely corroded,” and that a subcontractor’s equipment that was in “poor condition” had been left in hazardous areas. Because of these deficiencies, there is no assurance that the electrical equipment was safe and could not have caused the explosions.
Gas Detectors: Although gas detectors installed in the ventilation inlets and other critical locations were set to activate alarms on the bridge, they were not set to automatically activate the emergency shutdown (ESD) system for the engines or to stop the flow of outside air into the engine rooms. The bridge crew was not provided training or procedures on when conditions warranted activation of the ESD systems. Thus, when multiple gas alarms were received on the bridge, no one manually activated the ESD system to shut down the main engines. Had it been activated immediately upon the detection of gas, it is possible that the explosions in the engine room area could have been avoided or delayed.
Bypassed Systems: A number of gas detectors were bypassed or inoperable at the time of the explosions. According to the chief electronics technician, it was standard practice to set certain gas detectors in “inhibited” mode, such that gas detection would be reported to the control panel but no alarm would sound, to prevent false alarms from awakening sleeping crew members. Similarly, the crew bypassed an automatic shutdown system designed to cut off electrical power when ventilation system safety features failed, possibly allowing flammable gas to enter an enclosed area and reach an ignition source. The chief electrician had been told that it had “been in bypass for five years” and that “the entire fleet runs them in bypass.”
Design of the Main and Emergency Power Sources: Although the arrangement of main and emergency generators on DEEPWATER HORIZON met IMO MODU Code requirements to have completely independent engine-generator rooms along with independent power distribution and control systems, it did not prevent a total failure of the main electrical power system, when the explosions and fire damaged multiple generators and their related power distribution and control equipment. The design did not adequately take into account that the proximity of the air inlets to each other created a risk that flammable gases could impact all six generators at once.
Crew Blast Protection: DEEPWATER HORIZON did not have barriers sufficient to provide effective blast protection for the crew. Although the barriers separating the Drill Floor from adjacent crew quarters met the standards of the IMO MODU Code, those specifications are only designed to slow the spread of fire, not to resist an explosion. They did not prevent personnel in the crew accommodations area from sustaining injuries.
Command and Control: Because of a “clerical error,” by the Republic of the Marshall Islands, DEEPWATER HORIZON was classified in a manner that permitted it to have a dual-command organizational structure under which the OIM was in charge when the vessel was latched on to the well, but the master was in charge when the MODU was underway between locations or in an emergency situation. When the explosions began, however, there was no immediate transfer of authority from the OIM (Offshore Installation Manager) to the master, and the master asked permission from the OIM to activate the vessel’s EDS. This command confusion at a critical point in the emergency may have impacted the decision to activate the EDS".
The full report is available in this link.
"Failure to Use the Diverter Line: When the drilling crew directed the uncontrolled well flow through the Mud Gas Separator (MGS), the high pressure exceeded the system’s capabilities and caused gas to discharge on the Main Deck. Alternatively, the crew could have directed the well flow through a “diverter line” designed to send the flow over the side of the MODU (Mobile Offshore Drilling Unit). Although the diverter line also may have failed under the pressure, had it been used to direct the flow overboard, the majority of the flammable gas cloud may have formed away from the Drill Floor and the MODU, reducing the risk of an onboard explosion.
Hazardous Electrical Equipment: At the time of the explosions, the electrical equipment installed in the “hazardous” areas of the MODU (where flammable gases may be present) may not have been capable of preventing the ignition of flammable gas. Although DEEPWATER HORIZON was built to comply with IMO MODU Code standards under which such electrical equipment is required to have safeguards against possible ignition, an April 2010 audit found that DEEPWATER HORIZON lacked systems to properly track its hazardous electrical equipment, that some such equipment on board was in “bad condition” and “severely corroded,” and that a subcontractor’s equipment that was in “poor condition” had been left in hazardous areas. Because of these deficiencies, there is no assurance that the electrical equipment was safe and could not have caused the explosions.
Gas Detectors: Although gas detectors installed in the ventilation inlets and other critical locations were set to activate alarms on the bridge, they were not set to automatically activate the emergency shutdown (ESD) system for the engines or to stop the flow of outside air into the engine rooms. The bridge crew was not provided training or procedures on when conditions warranted activation of the ESD systems. Thus, when multiple gas alarms were received on the bridge, no one manually activated the ESD system to shut down the main engines. Had it been activated immediately upon the detection of gas, it is possible that the explosions in the engine room area could have been avoided or delayed.
Bypassed Systems: A number of gas detectors were bypassed or inoperable at the time of the explosions. According to the chief electronics technician, it was standard practice to set certain gas detectors in “inhibited” mode, such that gas detection would be reported to the control panel but no alarm would sound, to prevent false alarms from awakening sleeping crew members. Similarly, the crew bypassed an automatic shutdown system designed to cut off electrical power when ventilation system safety features failed, possibly allowing flammable gas to enter an enclosed area and reach an ignition source. The chief electrician had been told that it had “been in bypass for five years” and that “the entire fleet runs them in bypass.”
Design of the Main and Emergency Power Sources: Although the arrangement of main and emergency generators on DEEPWATER HORIZON met IMO MODU Code requirements to have completely independent engine-generator rooms along with independent power distribution and control systems, it did not prevent a total failure of the main electrical power system, when the explosions and fire damaged multiple generators and their related power distribution and control equipment. The design did not adequately take into account that the proximity of the air inlets to each other created a risk that flammable gases could impact all six generators at once.
Crew Blast Protection: DEEPWATER HORIZON did not have barriers sufficient to provide effective blast protection for the crew. Although the barriers separating the Drill Floor from adjacent crew quarters met the standards of the IMO MODU Code, those specifications are only designed to slow the spread of fire, not to resist an explosion. They did not prevent personnel in the crew accommodations area from sustaining injuries.
Command and Control: Because of a “clerical error,” by the Republic of the Marshall Islands, DEEPWATER HORIZON was classified in a manner that permitted it to have a dual-command organizational structure under which the OIM was in charge when the vessel was latched on to the well, but the master was in charge when the MODU was underway between locations or in an emergency situation. When the explosions began, however, there was no immediate transfer of authority from the OIM (Offshore Installation Manager) to the master, and the master asked permission from the OIM to activate the vessel’s EDS. This command confusion at a critical point in the emergency may have impacted the decision to activate the EDS".
The full report is available in this link.
Ammonia and thermal expansion
For my friends in the ammonia industry, let me remind you ammonia can also kill you in another way apart from exposure to it. 25 years ago, I witnessed a large leak due to thermal expansion of liquid ammonia which was not understood by the technical services team of the plant who had carried out an in house modification. The liquid ammonia which was blocked in, expanded due to thermal expansion and a pressure gauge in the line gave away, rocketing the gauge and causing a large leak. The flying projectile could have killed people.Airgas has published a technical bulletin about ammonia, which all personnel in ammonia facilities should read. Read it in this link.
April 23, 2011
Process Safety and Reaction calorimetry
In many batch processes, I keep observing companies hesitant to spend money to obtain reaction data prior to scale up to plant scale. The old adage "we have never done it before and nothing has happened" is often the answer. One incident that happens due to lack of understanding of reaction chemistry is enough to wipe out ALL your gains.An article written in 1991 points out the need for complete data prior to scale up to plant scale. One of the case studies mentioned is quoted below:
"A specific example of this type of approach was given by Homare Shinohara, of Eisai Chemical Co, who described the design of a manufacturing plant for pharmaceutical intermediates based on amino-thiaziazol carboxylic acid, generally known as F-15. Thiaziazol compounds are often used as a side chain at the 7-position of cephalosporin antibiotics. Thiaziazol carboxylic acid chloride (F-15Cl), for example, is being used at Eisai for the synthesis of two new antibiotics currently under development, E-1040 and E-1077. E-1040 is an injection drug, which is said to have the strongest bactericidal activity against Pseudomonas among the cephalosporins currently available, although less efficacious against Staphylococci. It is currently proceeding to Phase III testing. A development of E-1040, E-1077 is described as a fourth-generation cephalosporin having a wide spectrum of antibiotic activity from Gram-positives including Staphylococci to Gram-negatives including Pseudomonas. This compound is currently in e-phase II testing in Japan.
For the production of these compounds F-15 must be chlorinated. However, this intensely exothermic reaction can also produce two kinds of by-products: anti-F-15 acid chloride and phosphoric-amide-F-15 acid chloride. The resultant concentrations of these by-products is directly dependent upon the temperature of the reaction mass.
As a preliminary, the decomposition temperatures of the starting materials and final desired product were determined to confirm their safety. Shinohara's research team then used a Mettler Contalab to firstly determine the conditions required to suppress byproduct synthesis and then measure the heat of reaction to assist in the final plant design. To confirm the results the heats of reaction were also calculated using a Mettler RC 1.
It was determined that the reaction temperature should be maintained below -10ºC and that reaction heats generated depended upon the method of addition of phosphorus pentachloride - continuous, one or two portions. Although at 400 kJ/kg the reaction heats produced with continuous and one portion addition were 50kJ/kg higher than that for a two portion addition, possibly due to the absorption of heat by simultaneous crystallisation, it was decided to base the plant design on a 500-litre, glass-lined reactor with continuous addition of phosphorous pentachloride over a 30-minute period.
On calculation of the heat removal capacity of the jacket on the reactor using brine at -30¡C it was found to be insufficient to maintain the temperature below -10¡C. Further calculations determined the phosphorus pentachloride addition period would need to be extended to 3.3 hours, despite pilot-scale production of 5kg batches being satisfactorily achieved with additions over 30 minutes".
Read the full article with other examples in this link.
"A specific example of this type of approach was given by Homare Shinohara, of Eisai Chemical Co, who described the design of a manufacturing plant for pharmaceutical intermediates based on amino-thiaziazol carboxylic acid, generally known as F-15. Thiaziazol compounds are often used as a side chain at the 7-position of cephalosporin antibiotics. Thiaziazol carboxylic acid chloride (F-15Cl), for example, is being used at Eisai for the synthesis of two new antibiotics currently under development, E-1040 and E-1077. E-1040 is an injection drug, which is said to have the strongest bactericidal activity against Pseudomonas among the cephalosporins currently available, although less efficacious against Staphylococci. It is currently proceeding to Phase III testing. A development of E-1040, E-1077 is described as a fourth-generation cephalosporin having a wide spectrum of antibiotic activity from Gram-positives including Staphylococci to Gram-negatives including Pseudomonas. This compound is currently in e-phase II testing in Japan.
For the production of these compounds F-15 must be chlorinated. However, this intensely exothermic reaction can also produce two kinds of by-products: anti-F-15 acid chloride and phosphoric-amide-F-15 acid chloride. The resultant concentrations of these by-products is directly dependent upon the temperature of the reaction mass.
As a preliminary, the decomposition temperatures of the starting materials and final desired product were determined to confirm their safety. Shinohara's research team then used a Mettler Contalab to firstly determine the conditions required to suppress byproduct synthesis and then measure the heat of reaction to assist in the final plant design. To confirm the results the heats of reaction were also calculated using a Mettler RC 1.
It was determined that the reaction temperature should be maintained below -10ºC and that reaction heats generated depended upon the method of addition of phosphorus pentachloride - continuous, one or two portions. Although at 400 kJ/kg the reaction heats produced with continuous and one portion addition were 50kJ/kg higher than that for a two portion addition, possibly due to the absorption of heat by simultaneous crystallisation, it was decided to base the plant design on a 500-litre, glass-lined reactor with continuous addition of phosphorous pentachloride over a 30-minute period.
On calculation of the heat removal capacity of the jacket on the reactor using brine at -30¡C it was found to be insufficient to maintain the temperature below -10¡C. Further calculations determined the phosphorus pentachloride addition period would need to be extended to 3.3 hours, despite pilot-scale production of 5kg batches being satisfactorily achieved with additions over 30 minutes".
Read the full article with other examples in this link.
April 21, 2011
VFD's and process safety
VFD (Variable frequency drives) are used for conserving energy. The process safety issues when using VFD's must be considered when using them. To cut costs, some users try to install a single VFD for both the running and standby motors of a pump. This poses issues in safely locking out energy supply when one pump is given for maintenance. Read a good article on VFD's in this link.
April 19, 2011
Underground pipelines and excavation
An incident has occurred in Goa when a underground naphtha pipeline was punctured by accident by a JCB during excavation. It sparked off a major fire. As per the news item, "According to fire fighters and emergency service personnel, the incident occurred when a negligent heavy earth mover driver damaged an underground naphtha pipeline while undertaking excavation work.“It generated a spark, due to which traces in the naphtha pipeline burst into huge flames,” they informed.Immediately, after the pipeline was damaged, a blast occurred and flames reached upto 40 ft high and engulfed the earth moving excavator machine, 23 two-wheelers, six cars, three trucks, one tempo and one phosphoric acid tank, which were parked at the entrance gate of the industry.The JCB driver along with two labourers, who were standing nearby, sustained burn injuries and were rushed to a private hospital.Luckily, a major tragedy was averted, as two ammonia storage tanks of the industry are located barely 50 metres away from the entrance gate, where the fire incident occurred".
Read the news item in this link.
Read the news item in this link.
April 18, 2011
The importance of Inspection
A major fire incident in a gas turbine was traced to the improperly welded tubes in the natural gas regeneration coil section of the GT. Improper welding has given rise to many process incidents and it is important for you to have an adequately staffed inspection team to ensure proper welding procedures are followed and inspection is carried out. However, in many organisations, I observe an erosion of inspection capability as senior experienced personnel retire and are not replaced either due to lack of personnel or lack of experience. This is a recipe for disaster.
Read about the GT fire incident in this link.
Read about the GT fire incident in this link.
April 16, 2011
Lessons in process safety from Fukushima
The Fukushima nuclear accident continues to unfold. There are lessons to be learnt in process safety from the accident:
- Were your assumptions for the the worst case scenario correct? (The Fukushima plant suffered from both the earthquake and tsunami). The question I have asked is difficult to answer correctly because during the determination of worst case scenario, nothing bad has happened as yet and this will be weighing heavily on the minds of the decision makers. In other words, they may be wondering, why spend money on something that has never happened? The key word is "Never". How do you decide on probability of an event happening? Is your basis right? Are they supported by data?
- Are the set points of your automatic shutdown systems correct? (In the Fukushima accident, though some of the operational reactors automatically shutdown once seismic activity was detected, residual heat continued to be generated)
- Are your back up systems truly "back up"? There was no passive cooling water system available at Fukushima that would work even though cooling water pumps failed. It is reported that now in Indian nuclear reactors, authorities are planning to provide automatic shutdown for all reactors for seismic activity at a much lower setpoint than what the reactors are designed for. They are also thinking of providing batteries as power back up and connections for hook up of portable cooling water systems.
- I am sure that there will be also lessons to be learnt in disaster management once the full details of the accident are out.
April 14, 2011
Be aware of hazards of chemical cleaning
In 2009 an incident occurred during a chemical cleaning of a heat exchanger. 4 people reportedly died. Apparently, residual polymer was being removed from a heat exchanger by a chemical cleaning operation using 70% nitric acid when a chemical reaction caused pressure to build up and blew the contents of the heat exchanger out. Chemical cleaning of heat exchangers is often done during turnarounds. Ensure that a proper hazard analysis is carried out before you embark on such a cleaning. Often, the information about hazards will be available within the company but may not be known to the personnel who are carrying out the job.
Read about the incident in this link.
Read about the incident in this link.
April 12, 2011
Another steam turbine bites the dust - the dangers of overspeed
In February 2011 a steam turbine in a power plant in South Africa failed catastrophically when the overspeed trip system was being reportedly being tested. Luckily there were no casualties.
Steam that you cannot control can kill. See pictures of the accident in this link.
See my earlier post on dangers of turbine overspeed in this link.
Steam that you cannot control can kill. See pictures of the accident in this link.
See my earlier post on dangers of turbine overspeed in this link.
Process safety - Fires in insulation
Many fires, some of them devastating, have occurred due to fires caused by lube oil/ thermic fluid soaked insulation.
An article by Don Drewry and Dominique Dieken mentions the following on lube oil fires in steam turbines:
"Most steam turbines use mineral oil with a flash point ranging between 375 F and 500 F (190 to 260 Deg C). When sprayed onto a hot surface the oil will self-ignite at about 675 F (357 Deg C). Pressurized supply oil lines, if damaged, can compound the problem as atomized oil would be sprayed onto hot surfaces. Either self-ignition or a nearby ignition source can result in a three-dimensional fire at the bearing or lube oil piping with the burning oil flowing downward and collecting at ground level in the form of a pool fire.
The flame temperature of a lube oil fire, up to 2,100 F (1148 Deg C), can cause heat to be transferred to various turbine components through conduction, convection and radation. If there is flame impingement, the surface temperature of any exposed area can be expected to reach 2,100 F (1148 Deg C) within five minutes. As the temperature rises the turbine generator components expand at different rates. If this expansion is prevented because of geometric limitations, thermal stresses occur, which can exceed the yield strength of the materials and cause the components to fail.When a fire occurs the heat rising from the fire can also collect at the ceiling. If this happens the temperature can rise above 900 F and failure of the roof can occur. Likewise, a pool fire at ground level will quickly involve control and power cables beneath the turbine deck. Any extended exposure to heat will also damage the turbine's concrete pedestal".
Read the article in this link.
Fires have also occurred in reactors with coils that use thermic fluids to heat/cool the reactor. A presentation by John Griffiths mentions the following:
"Gas phase or liquid phase reaction?
Exothermic reaction of the liquid occurs as a result of oxidation by atmospheric oxygen. The liquid is dispersed over an enormous surface area within the structure.
How close to classical “thermal ignition”?
It all depends: if the fluid is very involatile at a typical temperature for exothermic reaction then the problem reduces to “thermal ignition”.The principles of lagging fires are the same – a breakdown of the balance between heat release and heat loss leads to thermal runaway.
So what are the distinctions from “thermal ignition”?
1.Vaporisation of the liquid can occur. It may be sufficiently rapid that most is dispersed, preventing self-heating taking place.
2.There can be an depletion of oxygen within the porous structure as a result of fuel vapour movement, but not necessarily enough to preclude oxidation.
3.The endothermic effect of vaporisation, contributes to the “heat loss” component.
4.Condensation is possible elsewhere in the structure (“giving back” the enthalpy of vaporisation).
Studies prior to ours erred towards involatile liquids so the most important distinctions (and features) of lagging fires were masked.
Is autoignition temperature of the fluid (AIT) relevant?
No (other than giving some indication of how reactive a substance might be)".
See the complete presentation in this link.
An article by Don Drewry and Dominique Dieken mentions the following on lube oil fires in steam turbines:
"Most steam turbines use mineral oil with a flash point ranging between 375 F and 500 F (190 to 260 Deg C). When sprayed onto a hot surface the oil will self-ignite at about 675 F (357 Deg C). Pressurized supply oil lines, if damaged, can compound the problem as atomized oil would be sprayed onto hot surfaces. Either self-ignition or a nearby ignition source can result in a three-dimensional fire at the bearing or lube oil piping with the burning oil flowing downward and collecting at ground level in the form of a pool fire.
The flame temperature of a lube oil fire, up to 2,100 F (1148 Deg C), can cause heat to be transferred to various turbine components through conduction, convection and radation. If there is flame impingement, the surface temperature of any exposed area can be expected to reach 2,100 F (1148 Deg C) within five minutes. As the temperature rises the turbine generator components expand at different rates. If this expansion is prevented because of geometric limitations, thermal stresses occur, which can exceed the yield strength of the materials and cause the components to fail.When a fire occurs the heat rising from the fire can also collect at the ceiling. If this happens the temperature can rise above 900 F and failure of the roof can occur. Likewise, a pool fire at ground level will quickly involve control and power cables beneath the turbine deck. Any extended exposure to heat will also damage the turbine's concrete pedestal".
Read the article in this link.
Fires have also occurred in reactors with coils that use thermic fluids to heat/cool the reactor. A presentation by John Griffiths mentions the following:
"Gas phase or liquid phase reaction?
Exothermic reaction of the liquid occurs as a result of oxidation by atmospheric oxygen. The liquid is dispersed over an enormous surface area within the structure.
How close to classical “thermal ignition”?
It all depends: if the fluid is very involatile at a typical temperature for exothermic reaction then the problem reduces to “thermal ignition”.The principles of lagging fires are the same – a breakdown of the balance between heat release and heat loss leads to thermal runaway.
So what are the distinctions from “thermal ignition”?
1.Vaporisation of the liquid can occur. It may be sufficiently rapid that most is dispersed, preventing self-heating taking place.
2.There can be an depletion of oxygen within the porous structure as a result of fuel vapour movement, but not necessarily enough to preclude oxidation.
3.The endothermic effect of vaporisation, contributes to the “heat loss” component.
4.Condensation is possible elsewhere in the structure (“giving back” the enthalpy of vaporisation).
Studies prior to ours erred towards involatile liquids so the most important distinctions (and features) of lagging fires were masked.
Is autoignition temperature of the fluid (AIT) relevant?
No (other than giving some indication of how reactive a substance might be)".
See the complete presentation in this link.
April 10, 2011
Explosions in power transformers and process safety
Numerous process incidents have been reported due to the failure of electrical power supply. There have been cases where back up power supply has also not come on line. Maintain your electrical power supply systems. A presentation by Dan Perco highlights the dangers of transformer oil tank explosions and the protection systems. Do not miss the last slide with a baby's photo in the presentation.
See the presentation in this link.
See the presentation in this link.
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