Level 1 Course 3 Unit 3 Slides - education.aiche.org · Title: Level 1 Course 3 Unit 3 Slides...

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SAChE® Certificate Program

Level 1, Course 3: Identifying and Minimizing Process Safety Hazards

Unit 3 – Examples: How Initiators Turn Hazards Into Incidents

Narration:

[None]


2

Objectives

Narration (male voice):

In Unit 2, we saw how the process industries can employ numerous techniques to identify

hazards and assess whether they’re being effectively managed. Now we’ll take a look at what

those hazards can lead to if unidentified or not well managed. By the end of this third unit in the

Identifying and Minimizing Process Safety Hazards course, titled “Examples: How Initiators Turn

Hazards into Incidents,” you will be able to:

• Explain the difference between a hazard and an initiator; and

• Identify the initiator(s) in a case study of an accident.


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SECTION 1: How Initiators Turn Into Incidents

Narration:

[None]


4

How Initiators Turn Hazards into Incidents


Take a look at this list of hazards and initiating events. Can you explain the relationship between

them?


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How Initiators Turn Hazards into Incidents (continued)


Hazards can become incidents once triggered by an initiating event. Outright failures (for

example, of instrumentation, mechanical equipment, or procedures), natural causes (such as an

earthquake or a lightning strike), or even adjacent events (like a nearby fire or power outage)

can all propagate into a wider incident.


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How Initiators Turn Hazards Into Incidents – Examples


There are several brief sections ahead in this unit. We’ll look at some different categories of

process equipment and how they became involved in incidents. For each situation, try to

identify the hazard and the initiator.


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SECTION 2: Example: Vessels

Narration:

[None]


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Vessel Example 1


In the example diagramed here, a 4000 gallon batch reactor is used to make an organic chemical

product by slowly adding a highly flammable and toxic liquid reagent to a pre-charged solid

reactant. The reaction is extremely energetic and susceptible to a violent runaway reaction.

The liquid charge rate is managed by a flow controller valve. The reactant flow rate is set at a

target that requires about 75% of the system’s cooling capacity. A high temperature alarm

closes the reagent charge valve.

Full flow through the line would exceed the system’s cooling capacity and shortly thereafter

initiate a violent runaway reaction with a two phase discharge through the vessel’s emergency

relief disc. The emergency relief of the vessel discharges to a dike on the other side of the wall.


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Vessel Example 1 (continued)


Now consider this same scenario in regard to this example…

The flow control system malfunctions, leading to overheating of the batch, causing a runaway

reaction, disc rupture, and release of material to the dike, giving rise to a toxic vapor cloud,

causing injuries and possible fatalities from toxic exposure.


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Vessel Example 2

Narration (female voice): Here’s another vessel example. This incident is taken from the CCPS Process Safety Beacon (at any time, you can pause and click the book icon to explore the Process Safety Beacon website). Narration (male voice): A large storage tank containing a flammable liquid overflowed. The spill was not detected until a security guard noticed a strong odor. He immediately reported his concern to operations personnel. Two operators responded, driving a truck to the area to investigate. Within minutes, there was a loud explosion followed by a fire. It’s believed that the truck provided the ignition source. It took emergency response personnel a day and a half to extinguish the fires which spread through the tank farm. More than a dozen employees were hospitalized and there was significant property damage. The incident investigation found that the tank was being filled and, unknown to the operators, the tank level gauge and the high level alarm had failed. The operators did not monitor the filling operation closely because they believed that the tank still had plenty of capacity. In this case, the tank was destroyed by the failure of relatively simple instrumentation.


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SECTION 3: Example: Mass Transfer Equipment

Narration:

[None]


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Mass Transfer Equipment Example 1


The following incident, again from the Process Safety Beacon, involves a centrifugal pump.

A 75 horsepower centrifugal pump was operated with both suction and discharge valves closed

for about 45 minutes. It was believed to be completely full of liquid. As mechanical energy from

the motor was transferred to heat, the liquid in the pump slowly increased in temperature and

pressure until, finally, the pump failed catastrophically. One fragment weighing five pounds was

found over 400 feet away. Luckily, no one was in the area so there were no injuries.


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Mass Transfer Equipment Example 1 (continued)


One of the simplest pieces of process equipment, when mismanaged, leads to outsized adverse

results.

Take a look at this illustration...

Energy from the impeller continues to be imparted to trapped liquid. That energy becomes heat,

which raises the temperature of the liquid, causing it to boil. Pressure builds. With the liquid

trapped in the pump casing, and having no place to go, the pump casing fails.

A procedural fault occurred. Notice that the valves on either side of the pump are closed.

In the next case, we’ll see the damage done by a deficiency in the simplest of mass transfer

equipment, a hose.


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Mass Transfer Equipment Example 2


On an offshore oil platform, operators were transferring methanol from a portable chemical

transporter tank connected by a hose to a storage tank. When the tank was lifted by a crane to

gravity feed the storage tank, methanol began spraying out from a hole in the hose.

The methanol ignited on the top deck. Methanol that was sprayed over the side also ignited by

the hot exhaust of a compressor located immediately below the transfer point on the second

deck. The fire was compounded by the breaking of the transfer tank's sight glass when a

crewman attempted to kick the valve closed. The fire spread as relief valves on two other

chemical transport tanks opened.

One man received second-degree burns. After the fires were extinguished, it was discovered

that the hose used to feed methanol from the transporter to the storage tank was split and had

been repaired with duct tape prior to the operation.


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SECTION 4: Example: Heat Transfer Equipment

Narration:

[None]


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Heat Transfer Equipment Example 1


In April 2010, the Tesoro refinery in Washington State experienced a catastrophic explosion due

to the rupture of one of its heat exchangers. As a result, there were seven fatalities and massive

damage to the facility.

Click the Video icon to open the Chemical Safety Board web page containing a 13 minute video

about the event. We’ll explore this example in more detail on the next few slides.


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Heat Transfer Equipment Example 1 (continued)


This is a schematic of the unit heat exchanger. Notice that there are two banks of three heat

exchangers: A/B/C bank and D/E/F bank. The E heat exchanger catastrophically ruptured.


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Heat Transfer Equipment Example 1 (continued)


Here are some key findings following the incident:

• The heat exchanger suffered a form of corrosion known as “high temperature hydrogen

attack.”

• This corrosion initiated a serious crack but the crack was insidious and difficult to detect.

• The unit was operating at very high temperature and pressure, exacerbating the

situation.

• When the unit failed, there was a sudden release of high temperature and flammable

hydrogen and naphtha, which instantly ignited on contact with air.


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Heat Transfer Equipment Example 2


Study this illustration.

If the shell side and tube side materials in a leaking heat exchanger are incompatible and

reactive, this can also initiate a serious incident. Heat and pressure can develop, with possible

equipment failure and escape of highly toxic or flammable materials.


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SECTION 5: Example: Valves and Piping

Narration:

[None]


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1.25 Valves and Piping Example


Consider this incident related to valves and piping (like many of the other examples we have

explored thus far in this unit, this example is from the CCPS Process Safety Beacon).

A plant was doing a pneumatic pressure test using air on a pipe connected to a tank. There was

no blind flange between the piping being tested and the tank.

The tank was isolated from the pressurized piping with a closed block valve. The block valve

leaked, allowing the pressure from the pneumatic test to leak into the tank. The tank (which

either didn't have a pressure relief device installed, or the pressure relief device was too small)

was over-pressurized and it failed at the bottom.

As shown in the photograph, the tank lifted into the air and came to rest on the top of the plant.


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Valves and Piping Example (continued)


Let's take a closer look at what happened in this incident...

Pneumatic test gas was entering the system. Without a blind flange, the gas flowed toward the

vessel. The valve leaked, allowing the test gas to enter the vessel unintentionally. Eventually,

excessive pressure built in the tank. A weak point in the vessel gave way and the tank shot into

the air.


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SECTION 6: Other Examples

Narration:

[None]


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Electrical Equipment Example

Narration (male voice): In this section, we’ll look at several other incidents. Let’s begin with an example involving electrical equipment. Again, the Process Safety Beacon is a great source of examples of things that have gone wrong in the area of process safety. This next one is from an activity that is actually ancillary to the actual chemical processing. The picture here is the typical result of an event that happens hundreds of times every year - an explosion. In this case, the "fuel" was believed to be hydrogen generated from the computer backup battery charging system seen in the background. Ventilation of this relatively small portion of the 50,000 square foot building was either not working or poorly designed. The small amounts of hydrogen released during the battery charging operation apparently accumulated and then an ignition source led to the explosion. As you can see in the photograph, the roof was blown off (about 400 square feet of roofing!); the damage is extensive, but no one was in the building, so luckily, no injuries occurred. This is a typical event. It happens all the time. This example is the result of a simple ventilator fan failing, along with the presence of an ignition source - a vacuum cleaner plugged in, for example - leading to serious damage.


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Fired Equipment Example


The CCPS Process Safety Beacon also has incidents involving fired equipment. In this example,

the heater was severely damaged during start-up as a result of a fire box explosion.

The operator had some difficulty with the instrumentation and decided to complete the start-up

by bypassing the interlocks on a one time only basis. This allowed the fuel line to be

commissioned with the pilots out.

The main gas valve was opened and gas filled the heater. Then...KABOOM!...the heater

exploded, destroying the casing and damaging several tubes. Fortunately, no one was injured.

The initiator here was a hot spot ignition source in the heater. You can see where human error

also played a significant role in this incident.


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External Event Example


Now let’s consider external events. These can be earthquakes, fires, tsunamis, sabotage, plane

crashes, and so on.

For example, consider a situation where a fire in a facility has spread to the underside of a

process vessel as illustrated here. If the equipment is improperly designed for this emergency, a

sequence of serious steps could take place.

Narration (female voice):

Drag the small vessel image along the timeline to explore these steps.


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Example Text Panel

[When Tank Slider is on ‘1’…]

Fire initially subjects the vessel to high heat flux.


Liquid temperature and vapor space pressure increase.


At the relief device set point, vapor begins venting to the outside allowing the temperature and

pressure in the vessel stabilize.


Below the liquid level, boiling liquid absorbs heat, preventing steel from overheating.


Ullage space undergoes a dramatic temperature increase; the unwetted upper portion of the

vessel eventually reaches a temperature the steel cannot withstand.


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The vessel shell, going beyond its design temperature, is weakened by heat, particularly from

thermally induced stresses near the vapor-liquid interface.


Combined with high internal pressure, a sudden violent tank rupture occurs.


Fragments of the pressure vessel may fly apart with great force.


People missed by flying fragments can still be injured by pressure of the escaping gas; buildings

and structures can also be damaged.


Most of the remaining superheated liquid vaporizes rapidly and a second pressure wave can

occur.


Some of the liquid is mechanically atomized, resulting in a fireball.


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Human Error Example


Let’s not forget human error. This tank collapsed when material was pumped out after

somebody had covered the tank vent to the atmosphere with a sheet of plastic during a

temporary cleaning activity.

The hazard here was the pressure differential being created by removing the tank’s contents

while not allowing any backfill from the atmosphere.

What was the initiator? You could make the case it was the operator blocking the vent with a

plastic sheet and then neglecting to remove it when the vessel was re-activated. Others might

say the initiator was the vessel’s discharge pump.


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Multiple Contributory Causes


Most of the incidents we have reviewed in this unit were precipitated by initiating events that

involved simple equipment items. However, in most process safety incidents and case studies,

there are several contributory causes.


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Process Safety Management System


As you progress through the SAChE Certificate Program, you’ll learn more about the process

safety management system and its many tools. Deficiencies in this area are very likely to allow

the initiating event to exist.


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Process Safety Management System (continued)


For example, let’s re-visit the tank liftoff incident. The leaking valve may have been the most

direct or proximate initiator for the event, but the next slide will show many of the other

underlying causes.

In the concluding remarks on the next page, note that the items in boldface indicate various

management elements necessary for an effective process safety management system. These are

covered throughout this online certificate program.


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Process Safety Management System (continued)


Asset integrity and operating procedures come into question right away.

• Did the test procedure really call for the closed block valve rather than an isolation blank? If

not, then personnel were not following the operating procedure for this test.

• How effective was asset integrity if this valve was leaking? Did the hazard analysis (if one was

done) actually pick up this scenario?

• Was process safety information used in the hazard analysis to assess the design basis of the

pressure relief vs possible scenarios? From the brief description here, it looks like this may be

the first time the pipe was tested at this section and in this way, possibly a non-routine activity.

• Was a management of change exercise conducted?


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Unit 3 Summary


We’ve reached the end of the Identifying and Minimizing Process Safety Hazards course. Having

completed this unit on How Initiators Turn Hazards into Incidents, you should now be able to:

• Explain the difference between a hazard and an initiator; and

• Identify the initiator(s) in a case study of an accident.

Before exiting, be sure to take the end-of-unit quiz. The Quiz Introduction is on the next slide.

Level 1 Course 3 Unit 3 Slides - education.aiche.org · Title: Level 1 Course 3 Unit 3 Slides...

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