Level 1 Course 2 - Hazard Recognition€¦ · 2 Objectives Narration (male voice): This is the second unit in the “Hazard Recognition” course. This unit is comprised of two sections.

Copyright ©American Institute of Chemical Engineers 2016. All rights reserved.

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SAChE® Certificate Program

Level 1, Course 2: Hazard Recognition

Unit 2 – Hazard Recognition Part 2

Narration:

[None]


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Objectives

Narration (male voice):

This is the second unit in the “Hazard Recognition” course. This unit is comprised of two sections.

In the first section, we’ll explore hazards related to the physical conditions of the materials or

the process. In Section 2, we’ll learn about hazards that are associated with the size of the

system.

By the end of this unit you will be able to:

• Identify hazards related to physical conditions, including temperature and pressure, of

the system; and

• Identify hazards which are related to the size of a system.


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SECTION 1: Hazards Related to the Physical Conditions of the Materials or

the Process

Narration:

[None]


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Hazards Related to Physical Conditions


Hazards can occur even when the materials present are relatively innocuous. The conditions,

such as temperature and pressure, of the material or the containers (or vessels) in which a

material is held can lead to hazards or make the inherent hazards worse.

For example, most people would not consider water to be inherently hazardous. However, in

the right circumstances, water can be very dangerous.


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Hazards of Boilers


Consider the case of water in a boiler. In boilers, water is transformed into steam by the

addition of heat. Furthermore, steam is almost always generated at high pressure. Pressure rises

when water is transformed into steam in a closed vessel. If there is no way for the steam to

escape, the vessel will explode.

Corrosion or overheating can also cause a sudden rupture of the boiler and an explosion.


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Grover Shoe Company


In the 19th century and early 20th century, boiler explosions were common occurrences.

The Grover Shoe Factory explosion was a seminal event, among others, that led to the

development of the American Society of Mechanical Engineers (or ASME) Boiler and Pressure

Vessel Code.

[Female voice]

Click the book icon if you would like to learn more about the ASME Boiler and Pressure Vessel

Code.


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History of Boiler Accidents – Resources

Narration (female voice):

There are many sources of information on the Internet to learn about the history of boiler

accidents. Click the images if you would like to explore some of these resources.


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Hazards of Boilers (continued)


Despite the fact that under ordinary circumstances water is an innocuous substance, the

pressure within a boiler is sufficient to initiate an explosion. It’s the conditions inside the boiler,

not the inherent properties of water, that make it a potential hazard.

It is worth noting that steam systems and boilers are quite common in chemical facilities, so it’s

probable that chemical engineers will encounter them in the course of their careers.


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Hazards Related to Physical Conditions


It is not unusual for physical conditions to be the cause of a release of inherently hazardous

materials. On the next few slides, we’ll examine such a case.


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Example: Gas Processing Facility


In 1998, a major explosion and fire occurred at a gas processing facility in Victoria, Australia. The

facility separated methane from Liquefied Petroleum Gas (or LPG). While the materials present

(in this case, hydrocarbons) in this process are inherently hazardous because they are flammable,

it was actually the conditions in the process that initiated the release of a large quantity of

hydrocarbons.


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Example: Gas Processing Facility (continued)


The exact sequence of events that led to the accident is complicated, but the result was that the

temperature in one of the pieces of equipment in the process (a heat exchanger) dropped to

minus 48 degrees Celsius.

Normal carbon steel is susceptible to brittle fracture (the type of failure that occurs when a

banana is frozen in liquid nitrogen and then smashed on a table) at temperatures below about

minus 29 degrees Celsius.


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Warm “lean oil” was introduced into the heat exchanger that was cold; the “lean oil” was much

hotter than the heat exchanger itself. The large temperature difference between the lean oil

and the metal in the heat exchanger created enough stress to cause a brittle fracture.


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Rupture of the heat exchanger led to the release of large quantities of flammable vapor, leading

to a subsequent fire and a series of explosions. The fire burned for two days. Two employees

were killed and eight were injured. The plant was destroyed and two nearby plants at the same

site were damaged.


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It would be a mistake to point to temperature as the sole cause of this accident. Accidents

generally involve multiple failures. Nevertheless, physical conditions - the temperatures of the

heat exchanger and the fluids flowing though it - played a critical role in initiating the release of

flammable materials.

The flammable nature of the materials present only became relevant after the heat exchanger

ruptured and allowed them to escape.


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A complete report on the accident entitled “The Esso Longford Gas Plant Accident” was

published by the state of Victoria, Australia. A summary also appears in the “Process Safety

Beacon - Cold Embrittlement and Thermal Stress.”

[Female voice]

Click the book icons if you would like to read either document.


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Hazards Related to Physical Conditions – Hydraulic Shock Example


There are examples of physical conditions other than temperature or pressure that led to

catastrophic events.

Hydraulic shock can occur where there’s a rapid change of velocity and momentum of the liquid

flowing through piping. It’s sometimes referred to as “water hammer.” If you’ve ever closed a

water faucet rapidly and heard the water pipes make a knocking sound, you’ve experienced one

form of hydraulic shock.

In August 2010, hydraulic shock of piping led to the release of 15,000 kilograms (32,000 pounds)

of anhydrous ammonia at a facility which used ammonia as a refrigerant. Note that it wasn’t the

properties of ammonia that caused the release; instead, a physical phenomenon was the cause.

[Female voice]

See the CSB Report on the Millard Refrigerated Services ammonia release for more information

on this event.


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Hazards Related to Physical Conditions – Dust Explosion Example


It’s not unusual for combustible dusts to ignite and explode. In this case, it’s the fact that the

material is present as a fine powder or dust dispersed in air which renders it susceptible to an

explosion. Common combustible materials, which seem innocuous, can be dangerous when they

are finely divided and dispersed in air.

Grain silos have exploded because they contain grain dust suspended in air. Similar events can

occur in industrial operations where combustible dusts are handled.

[Female voice]

For some examples, see the CSB reports on the “Imperial Sugar Company Dust Explosion and

Fire” and the “AL Solutions Fatal Dust Explosion” by clicking the book icons shown.


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Hazards Related to Physical Conditions – Summary


As we conclude Section 1, keep in mind that physical conditions can result in hazards, even

when the materials are inert and innocuous. Hazards related to physical conditions are just as

important to recognize as hazards inherent to a material because physical conditions can start a

chain of events that leads to a release of a hazardous material.


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SECTION 2: Hazards that are Associated with the Size of the System

Narration:

[None]


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Hazards that are Associated with the Size of the System


Back in Unit 1, we looked at hazards that are inherent properties of the materials used or

manufactured in the process. Then in Section 1 of this unit we looked at hazards related to the

physical conditions of the materials or the process. Here in Section 2 of Unit 2, you’ll learn why

the size of a system is also important.


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Hazards that are Associated with the Size of the System (cont.)


The size (or scale) of a system affects the extent of hazards associated with it. It can create a

hazard that would otherwise not exist, or worsen an existing hazard. The release of a large

quantity of a material contained within a process is generally more severe than the release of a

small quantity.

One way to understand hazards resulting from the size of a system is to compare the sizes and

impacts of items and materials you might find in an ordinary home and similar items and

materials you might find in industry. Of course, many items and materials used in industry

systems would never be present in an ordinary home, and so a direct comparison is not possible.

But some are.


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Example Material: Ammonium Nitrate


Let’s look at an example material.

Ammonium nitrate is commonly used as a fertilizer on farms, and it may be present in small

quantities in an ordinary home. Most people would hardly consider a bag of fertilizer to be

dangerous. In fact, ammonium nitrate is quite safe at ambient temperature and pressure. It

doesn’t burn. In small amounts, it’s harmless. But when ammonium nitrate is heated in a

confined space, it can decompose rapidly and detonate.

Three U.S. agencies - the Environmental Protection Agency (EPA), the Occupational Safety and

Health Administration (OSHA), and the Bureau of Alcohol, Tobacco, Firearms and Explosives

(ATF) - prepared a chemical advisory document on the safe storage, handling, and management

of solid ammonium nitrate prills (prills are small beads).

[Female voice]

Click the document image if you would like to take a look at this document now.


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Example Case: Ammonium Nitrate


On April 17, 2013 a fire broke out in a fertilizer storage and distribution facility in the town of

West, Texas. The facility stored large amounts of ammonium nitrate for use as a fertilizer. The

fire caused approximately 27 metric tons (or 30 tons in Imperial units) of ammonium nitrate to

detonate. The site itself and buildings near the site were destroyed.

The explosion led to extensive damage and destruction in the town of West, Texas. It also

caused 15 fatalities and many more injuries.


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Example Case: Ammonium Nitrate (continued)


The middle school located eight tenths of a kilometer (or one-half mile) away from the explosion

was heavily damaged. This video shows the extent of the damage to the town.


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Example Case: Ammonium Nitrate (continued)


The CSB noted that the use of combustible materials at the site introduced the risk of a fire,

which could then trigger an ammonium nitrate explosion.

Regardless of the reason for the fire and explosion (and despite the fact that the fire was

deliberately set), one of the lessons is that the large volume of ammonium nitrate stored at the

facility created a hazard that does not exist with an ordinary 10 or 20 kilogram bag of fertilizer.

In other words, the size of the system strongly influences the extent of the hazard.

Note that there are many factors which can contribute to an accident, and the cause was not

the amount of ammonium nitrate in storage. Nevertheless, the amount of the ammonium

nitrate present affected the magnitude of the disaster. If a smaller amount had been present, it

would have affected a smaller area of the community or none at all.

[Female voice]

Click the book icon to review the report prepared by the CSB as a result of this accident.


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CSB Report Regarding West Fertilizer (Slide Layer)


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Example Material – LPG


Another example of the impact of size involves Liquefied Petroleum Gas (or LPG). LPG is a fuel

which is especially useful for cooking and heating (and so it’s naturally flammable). It’s used in

both homes and industry. Like other materials, it’s stored in large quantities at facilities where

it’s produced or at facilities that distribute LPG to customers.


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Example Material – LPG (continued)


For example, a reasonable size for an LPG tank used for home heating would be 1.9 cubic meters

(equivalent to 1900 liters or 500 gallons). By contrast the largest LPG tanks located at a Mexico

City LPG terminal, which in 1984 experienced a fire and multiple explosions, contained 2400

cubic meters or 634,000 gallons of LPG.


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Example Case – LPG


The Mexico City facility had six spherical storage tanks and 48 smaller horizontal cylindrical tanks.

On November 19th, 1984 an LPG leak occurred at the Mexico City terminal. The exact cause

could not be determined with certainty after the event because of the extent of the damage to

the site.

The LPG leak continued for five to ten minutes and a cloud of LPG vapor estimated to be 200

meters by 150 meters by two meters high formed. The cloud ignited. The explosion knocked

storage tanks off their supports and ruptured piping, causing more LPG to be released.

A series of explosions which destroyed the site followed. In addition to destroying the facility,

the fire and explosions killed 600 people and injured 7000 others. Most of the casualties were

members of the public living in surrounding communities.


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Example Case – LPG (continued)


Like the ammonium nitrate example, many factors contributed to the extensive destruction and

loss of life, not just the amount of LPG. At the same time, the level of destruction and loss of life

was related to the amount of LPG in storage (the size of the system). The consequence of an

explosion involving the contents of an LPG tank installed at a house would be very different.


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It’s possible to demonstrate the difference between a release of 2400 cubic meters of LPG and a

release of 1.9 cubic meters of LPG (the amount that might be present in a home LPG tank).

There are many assumptions in these calculations, and these assumptions do not necessarily

apply to the situation at the Mexico City terminal. These calculations are simply intended to

illustrate the difference between possible impacts of releasing a small amount of LPG versus a

large amount.


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A vapor cloud explosion involving 1.9 cubic meters (or 920 kilograms) of LPG would produce an

overpressure of 0.0069 bar (or 0.1 psi) at a distance of two tenths of a kilometer from the

explosion. A 0.0069 bar overpressure can cause windows to break.

A vapor cloud explosion involving 2400 cubic meters (or 290,000 kilograms) of LPG would cause

a 0.0069 bar overpressure and break windows 1.8 kilometers away. Outside these distances,

people are unlikely to be seriously injured.

So the explosion of a home LPG tank might cause damage a few houses away whereas the

explosion of a large LPG tank, by contrast, might damage or destroy entire communities.

[Female voice]

A short summary of the Mexico City LPG event can be found by clicking the book icon.


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Hazards that are Associated with the Size of the System – Summary


The size of a system influences how hazardous it is. Naturally, large systems can have a larger

impact than small systems. The impact of a release of a hazardous material can have a

significant impact and can endanger not only employees but members of the public.


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Unit 2 Summary


We’ve reached the end of the second unit in the Hazard Recognition course. This second unit

was comprised of two sections. In the first section, we looked at hazards related to the physical

conditions of the materials or the process and in the second section we examined hazards that

are associated with the size of the system.

You should now be able to:

• Identify hazards related to physical conditions, including temperature and pressure, of the

system; and

• Identify hazards which are related to the size of a system.

Be sure to take the end-of-unit quiz beginning on the next slide before closing the unit.

Level 1 Course 2 - Hazard Recognition€¦ · 2 Objectives Narration (male voice): This is the second unit in the “Hazard Recognition” course. This unit is comprised of two sections.

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