Process Safety Level 1 - Unit 2 Hazard Recognition

SAChE® Certificate Program: Hazard Recognition

Author: Dennis Bernhard Reviewer: Tom Degnan

Part 3: Hazards related to the

physical conditions of the materials or the process

Process Safety Level 1 - Unit 2 Hazard Recognition

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 (vessels) in which a material is held can lead to hazards or make the inherent hazards worse.

• Most people would not consider water to be inherently hazardous. However, in the right circumstances, it can be very dangerous.

Process Safety Level 1 - Unit 2 Hazard Recognition

Hazards Related to Physical Conditions

Consider the case of water in a boiler

Process Safety Level 1 - Unit 2 Hazard Recognition

A Modern Boiler

Process Safety Level 1 - Unit 2 Hazard Recognition

Picture © Hurst Boiler & Welding Co., Inc.

Hazards of Boilers

• In boilers, water is transformed into steam by the addition of heat.

• Furthermore, steam is almost always generated at high pressure.

• In any case, the 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.

• In the 19th century and early 20th century, boiler explosions were common occurrences. The frequency of boiler explosions led the American Society of Mechanical Engineers (ASME) to create its Boiler and Pressure Vessel Code.

Process Safety Level 1 - Unit 2 Hazard Recognition

More Information on the History of Boilers

• There are many sources of information on the internet for more information on the history of boiler accidents, including:

• https://en.wikipedia.org/wiki/Grover_Shoe_Factory_disaster

• https://www.asme.org/engineering-topics/articles/boilers/the-history-of-asmes-boiler-and-pressure

• https://www.asme.org/engineering-topics/articles/boilers/the-greatest-maritime-disaster-in-u-s-history

• https://www.asme.org/engineering-topics/articles/boilers/the-true-harnessing-of-steam

• https://www.asme.org/about-asme/engineering-history Process Safety Level 1 - Unit 2 Hazard

Recognition

An Early 20th Century Boiler Explosion

The Grover Shoe Factory Explosion was a Seminal Event in the Development of the ASME Boiler and Pressure Vessel Code

Process Safety Level 1 - Unit 2 Hazard Recognition

Taken from “History of the Brockton Relief Fund” by Albert F. Pierce, March , 1905.

Hazards of Boilers

• The point is that boilers contain a fluid (water) which is non-toxic, non-flammable, and under most circumstances non-reactive.

• Nevertheless, the pressure within a boiler is sufficient to initiate an explosion.

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

Process Safety Level 1 - Unit 2 Hazard Recognition

Hazards Related to Physical Conditions

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

materials

Process Safety Level 1 - Unit 2 Hazard Recognition

Example Case – Gas Processing Facility

• In 1998, a major explosion and fire occurred at a gas processing facility in Victoria, Australia that separated methane from Liquefied Petroleum Gas (LPG).

• While the materials (hydrocarbons) present 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.

Process Safety Level 1 - Unit 2 Hazard Recognition

Example Case – Gas Processing Facility

• 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 (a heat exchanger) in the process dropped to -48° C.

• 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 -29° C.

Process Safety Level 1 - Unit 2 Hazard Recognition

Example Case – Gas Processing Facility

• 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 hot lean oil and the metal in the heat exchanger created enough stress to cause a brittle fracture.

Process Safety Level 1 - Unit 2 Hazard Recognition

Example Case – Gas Processing Facility

• 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. Eight were injured. • The plant was destroyed, and two nearby plants at

the same site were damaged.

Process Safety Level 1 - Unit 2 Hazard Recognition

Esso Longford Facility after the explosion

Process Safety Level 1 - Unit 2 Hazard Recognition

Example Case – Gas Processing Facility

• 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.

Process Safety Level 1 - Unit 2 Hazard Recognition

Example Case – Gas Processing Facility

• 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 located in the resources tab on the top right hand corner of the slide.

Process Safety Level 1 - Unit 2 Hazard Recognition

Hazards Related to Physical Conditions – Other Examples

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

to catastrophic events

Process Safety Level 1 - Unit 2 Hazard Recognition

Other Examples – Hydraulic Shock

• Hydraulic shock can occurs where is a rapid change of velocity and momentum of the liquid flowing through piping. It is sometimes referred to as “water hammer”.

• If you have 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 kg (32,000 lbs) of anhydrous ammonia at a facility which used ammonia as a refrigerant.

• See the CSB Report on the Millard Refrigerated Services Ammonia Release for more information on this event.

• The important point for now is that it wasn’t the properties of ammonia that caused the release.

• Instead a physical phenomenon was the cause.

Process Safety Level 1 - Unit 2 Hazard Recognition

Other Examples – Hydraulic Shock

A pipe broken as a result of hydraulic shock at Millard Refrigerated Services, Inc. in August 2010.

Process Safety Level 1 - Unit 2 Hazard Recognition

Taken from CSB Report “Key Lessons for Preventing Hydraulic Shock in Industrial Refrigeration Systems: Anhydrous Ammonia Release at Millard Refrigerated Services, Inc.”, January 2015.

Other Examples – Dust Explosions

• It is not unusual for combustible dusts to ignite and explode • In this case it is 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

• For some examples, see the CSB reports on the Imperial Sugar Company Dust Explosion and Fire and the AL Solutions Fatal Dust Explosion

Process Safety Level 1 - Unit 2 Hazard Recognition

Other Examples – Dust Explosions

The Imperial Sugar Company facility after a dust explosion on February 7, 2008.

Process Safety Level 1 - Unit 2 Hazard Recognition

Taken from CSB Report “Investigation Report Sugar Dust Explosion and Fire”, September 2009.

Summary – Hazards Related to Physical Conditions

• Physical conditions can result in hazards, even when the materials present in a process are inert.

• 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.

Process Safety Level 1 - Unit 2 Hazard Recognition

Part 4: Hazards that are

associated with the size of the system

Process Safety Level 1 - Unit 2 Hazard Recognition

Hazards Resulting from the Size of a System

• For far we have looked at hazards that are • inherent properties of the materials used or

manufactured in the process, or • related to the physical conditions of the

materials or the process. • The size of a system is also important.

Process Safety Level 1 - Unit 2 Hazard Recognition

Hazards Resulting from the Size of a System

• 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.

Process Safety Level 1 - Unit 2 Hazard Recognition

Hazards Resulting from the Size of a System

• 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. Process Safety Level 1 - Unit 2 Hazard

Recognition

Example Case – Ammonium Nitrate

• 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 is harmless. • But when it is heated in a confined space, it can decompose

rapidly and detonate. • Please see the link in the resources tab at the top right hand

corner of this slide for information on the Management of Solid Ammonium Nitrate Prills.

Process Safety Level 1 - Unit 2 Hazard Recognition

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 tonnes (30 tons) of ammonium nitrate to detonate.

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

• It also caused 15 fatalities and many more injuries. • Please see the resources tab for the CSB investigation

of the explosion. Process Safety Level 1 - Unit 2 Hazard

Recognition

Example Case – Ammonium Nitrate

• The site was completely destroyed.

Process Safety Level 1 - Unit 2 Hazard Recognition

From US Chemical Safety Board; West Explosion Photo by CSB investigator Mark Wingard, who surveyed the site with a remote-controlled aircraft.

Example Case – Ammonium Nitrate

• This video shows the extent of the damage to the town.

• Buildings near the site were destroyed, and the middle school located 0.8 km (0.5 mile) away from the explosion was heavily damaged.

Process Safety Level 1 - Unit 2 Hazard Recognition

Example Case - Ammonium Nitrate

• 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, 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 kg bag of fertilizer.

• In other words, the size of the system strongly influences the extent of the hazard. Process Safety Level 1 - Unit 2 Hazard

Recognition

Example Case - Ammonium Nitrate

• 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.

• And if the amount had been small enough, there would have been no impact at all on the community.

Process Safety Level 1 - Unit 2 Hazard Recognition

Example Case - LPG

• Another example of the impact of size involves Liquefied Petroleum Gas (LPG).

• LPG is a fuel which is especially useful for cooking and heating (and so it is naturally flammable).

• It is used in both homes and industry. • Like other materials, it is stored in large quantities

at facilities where it is produced or at facilities that distribute LPG to customers.

Process Safety Level 1 - Unit 2 Hazard Recognition

Example Case - LPG

• For example, a reasonable size for a Liquefied Petroleum Gas (LPG) tank used for home heating would be 1.9 m3 (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 2,400 m3 of LPG.

Process Safety Level 1 - Unit 2 Hazard Recognition

Example Case - LPG

• The Mexico City facility had 6 spherical storage tanks and 48 smaller horizontal cylindrical tanks.

• On 19 November 1984 an LPG leak occurred at the Mexico City terminal. The exact cause could not be determined with certainty after the event because of damage to the site.

• In any case, the LPG leak continued for 5-10 minutes and a cloud of LPG vapor estimated to be 200 m x 150 m x 2 m high formed.

• The cloud ignited. The explosion knocked storage tanks off their supports and ruptured piping, causing more LPG to be released.

Process Safety Level 1 - Unit 2 Hazard Recognition

Example Case - LPG

A burning propane sphere.

Process Safety Level 1 - Unit 2 Hazard Recognition

Example Case - LPG

• 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.

• Again, many factors contributed to this level of 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 much different.

Process Safety Level 1 - Unit 2 Hazard Recognition

Example Case - LPG

The aftermath of the fire and explosion.

Process Safety Level 1 - Unit 2 Hazard Recognition

Example Case - LPG

• It is possible to demonstrate the difference between a release of 2400 m3 of LPG and a release of 1.9 m3 of LPG (the amount that might be present in a home LPG tank).

• There are many assumptions in these calculations, and these assumption do not necessarily apply to the situation at the Mexico City terminal.

• They are simply intended to illustrate the difference between possible impacts of releasing a small amount of LPG vs. a large amount.

Process Safety Level 1 - Unit 2 Hazard Recognition

Example Case - LPG

• A vapor cloud explosion involving 1.9 m3 (920 kg) of LPG would break windows 0.2 km away. This is the distance to a 1 psi overpressure.

• A vapor cloud explosion involving 2400 m3 (290,000 kg) of LPG would break windows 1.8 km 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.

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

Process Safety Level 1 - Unit 2 Hazard Recognition

Example Case - LPG

• A short summary of the event can be found in the Process Safety Beacon – LPG Tragedy located in the resources tab.

Process Safety Level 1 - Unit 2 Hazard Recognition

Summary – Hazards Resulting from the Size of a System

• 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 by members of the public.

Process Safety Level 1 - Unit 2 Hazard Recognition