Everything You Ever Wanted to Know About Thermal Runaway

Reactivity hazards are part of the safety, health, and environment (HSE) topic for the Fundamentals of Engineering (FE) Chemical exam. Runaway reactions are associated with reactivity hazards and are also an important safety concern in the industry. Past major industrial accidents and fatalities have occurred due to runaway reactions, and they are still a factor for consideration today. Thermal runaway is an out-of-control exothermic reaction (releases heat) that can lead to devastating consequences. These reactions can become uncontrollable rapidly and are not easily contained by firefighters and first responders.

The blog covers:

1. The Fire Triangle

2. Assessing Thermal Runaway Firefighting Techniques

3. Texas City Disaster

4. Noticing Smoke

5. Effect of Pressurized Steam

6. Effect of Other Volatile Components

7. The New London School Explosion

8. Born from a Spark

1. The Fire Triangle

The fire triangle is the science behind stopping a flammability hazard and stopping a runaway reaction. Heat, fuel, and an oxidizing agent (oxygen) are the three (3) components that comprise the fire triangle. At least one of the components must be eliminated to stop the reaction and extinguish the fire, and while you only need to eliminate one of the three components, this can prove to be a very difficult and daunting task. Care must be taken to mitigate and prevent the fire triangle from coming to fruition. The fire triangle is also established by the General Combustion Stoichiometric Equation:

Fuel + Oxygen -> Carbon Dioxide + Water

Different fuel sources (e.g., methane, propane) will have different stoichiometric quantities, but this is the general formula. Nitrogen (N₂) is inert and does not react, so it is often excluded from stoichiometry. But remember that air is approximately 78% nitrogen and 21% oxygen, so while nitrogen may not be relevant, it is still present. Combustion is also an exothermic reaction (releases heat) process that shares similarities with thermal runaway (I think of thermal runaway as being excessive combustion). Incomplete combustion can also cause health hazards by generating carbon monoxide (CO) poisoning due to inadequate oxygen (CO vs CO₂). Because of potential CO exposure, it is critical to ensure you have good ventilation and unblock any obstructions since incomplete combustion can occur anywhere (home, business, plant, etc.) at any time.

2. Assessing Thermal Runaway Firefighting Techniques

Thermal runaway occurs when surplus heat speeds up a reaction, so the reaction rate increases, more heat is released, and the reaction happens faster and with more severity in a vicious cycle. This can become uncontrollable and cause dangerous fires and explosions that can be damaging and increasingly difficult to contain. Heat removal can slow the reaction (eliminating one of the Fire Triangle components), but this is difficult to achieve as a thermal runaway reaction rapidly becomes more powerful. Fires and explosions due to thermal runaway can easily overwhelm firefighting techniques, so location is a factor when assessing facilities where thermal runaway can occur. Fires can spread rapidly, to begin with, and adding reactivity hazards will only be more disastrous.

3. Texas City Disaster

One past industrial accident of thermal runaway severity was the Texas City Disaster (1947). The SS Grandcamp was docked at the port of Texas City in Galveston Bay. Ammonium nitrate (NH₄NO₃) detonated on a cargo ship that triggered subsequent runaway reactions, which led to fires and explosions of other cargo ships and oil facilities, ultimately leading to the deadliest industrial accident in United States history (still stands today). You can see from my description that a fire started the detonation and evolved into the severe vicious cycle that I mentioned earlier. The ammonium nitrate was also stored at higher temperatures, increasing both its chemical activity and likelihood of generating an explosion.

4. Noticing Smoke

Crew members first noticed smoke in the SS Grandcamp cargo hold and tried using water and fire extinguishers to stop the fire (eliminate the fire triangle components). When this proved to be ineffective, the captain authorized sealing all hatches to smother the fire by removing its oxygen content and filling the cargo hold with steam. On a smaller scale, lids are often used to smother skillets so you can prevent kitchen fires. By eliminating the oxygen, the fire cannot "breathe", so it ends before a kitchen fire can become more severe. However, nitrate (NO₃) is an oxidizer, so not only was this ineffective on the SS Grandcamp, but it may also have strengthened the fire (steam contributed more heat to the fire). Scientific data and technology have certainly improved over the years since 1947, so it is possible that the SS Grandcamp crew may not have realized this mistake. Closing the hatches would have also prevented ventilation for the oxidizing agent.

5. Effect of Pressurized Steam

The pressurized steam blew off the cargo hatches, and the SS Grandcamp detonated shortly after, due to the excessive heat and pressure. Thermodynamics (8-12 Questions) is another key topic on the FE Chemical exam, with steam tables listed in the FE Reference Handbook (v 10.0.1, p. 157-158). Remember that exam topics tend to overlap, so you can use knowledge of certain exam content to help with other exam questions. Water becomes steam at its 100° C (212° F) boiling point for standard pressure conditions (1 atm = 14.7 PSIA). Since steam is already at 212° F when entering the volatile cargo hold, you can see how the pressurized steam heat was contributing towards the fire intensity.

6. Effect of Other Volatile Components

The state of Texas is one of the largest industrial producers in the United States (oil, gas, chemicals, etc.), so there were other volatile components impacted, furthering the catastrophe. Because the SS Grandcamp was docked in port, other vessels and watercraft were destroyed too; this was essentially a total loss in the port of Texas City. The explosive blast levelled buildings and destroyed chemical plants; debris flying at supersonic speeds punctured infrastructure, causing leaks of other volatile components. The nearby town of Galveston also suffered infrastructure losses and fatalities. Because the fires were so ferocious, first responders from other locations were unable to immediately reach the disaster site; again, the severity of thermal runaway should not be taken lightly. The vicious cycle of reactions can produce a fire that can become almost unstoppable (there were two explosions at the port, with the second explosion occurring due to the first explosion, succeeding the cycle).

7. The New London School Explosion

The New London School explosion (1937) was another industrial accident caused by the fire triangle and combustion. Texas was growing as a prosperous industrial hub with the discovery and exploration of oil wells, so businesses and communities were booming despite the Great Depression in the United States. The New London School was erected as a new educational institution; however, the school board made two (2) mistakes that contributed to the explosion. The first decision was opting for the installation of gas heaters throughout the building rather than choosing a steam distribution system. It is not practical or safe to install individual heaters throughout a building; it was probably considered cheaper at the time, but a distribution system is more effective. The individual gas heaters were all devices producing volatile fuel (fire triangle component).

8. Born from a Spark

The second fatal mistake was the school board cancelling their natural gas contract in favor of plumbers installing a residual gas line to feed the building and its gas heaters. Residual gas was a by-product of extracted oil, so major oil companies were not bothered by this practice; it did not impact their operations or profits. However, the residual gas line was tapped and installed poorly, causing a gas leak that was building up inside the school. With the gas fuel and oxygen, there were now two (2) components of the fire triangle. The last component was when Lemmie R. Butler (workshop instructor) incurred a spark from an electric sander (an ignition source can count as heat in the fire triangle). The gas-air mixture was volatile and ignited, causing widespread damage and structural collapse at New London School. Fortunately, unlike the Texas City disaster, there were no other volatile facilities nearby, so the school explosion did not lead to subsequent reactions and explosions. The reaction explosion occurred at the school only, and there were no other additional sources of heat to strengthen the frequency or severity of combustion.

Conclusion

In the aftermath of industrial accidents, the Texas Engineering Practice Act has since been enacted and amended to reflect legislation from public backlash. This act describes that practicing engineers must have professional engineering registration with the state of Texas to have the engineer title (most recent rules are effective as of June 2017). Ethics and Professional Practice (3-5 Questions) are another topic on the FE Chemical exam, and again, you should note how the exam topics overlap. There have been many other industrial accidents that were encountered by our engineering predecessors. While very unfortunate, they always provide a good learning experience to improve upon processes and safety. You can certainly find more industrial information online and check back with School of PE for more blog posts about industry discussion.

Do you have a certain fiery passion for engineering? Get into the exam preparation hot seat with School of PE and access subject-matter expert instruction, innovative learning technology, and more-all designed to help build your confidence for exam day! Contact us to learn more!

About the Author: Gregory Nicosia

Gregory Nicosia, PE is an engineer who has been practicing in the industry for eight years. His background includes natural gas, utilities, mechanical, and civil engineering. He earned his chemical engineering undergraduate degree at Drexel University (2014) and master's in business administration (MBA) from Penn State Harrisburg (2018). He received his EIT designation in 2014 and PE license in 2018. Mr. Nicosia firmly believes in continuing to grow his skillset to become a more well-rounded engineer and adapt to an ever-changing world.

How to Ask Your Boss for a Raise or Promotion

Engineers seeking to increase their compensation often are uncertain as to how to approach their supervisors. While there are certainly no "one size fits all" rules for how to achieve a salary increase, there are a few things to keep in mind which may be helpful in determining the best approach.

Determining Employee Compensation

Employee compensation is determined by several factors which include: the employee's experience level, knowledge, skills, and educational background; job market conditions; industry market conditions; company-specific needs and goals; and other factors. Understanding the particular conditions and needs of the company is important because ultimately the personal success of an employee, in terms of compensation, job satisfaction, and career advancement, hinges on the successful alignment of the employee's and the company's goals. Proving yourself as a valuable asset for a company's success is a key factor in career advancement within a company. Quite simply, an employee who noticeably adds value to a company is most likely to be valued in return. Demonstrating this value through quality work is one means towards recognition. Making the quality of the work you do an advertisement for your own advancement is one strategy in working towards this end. Doing this work with a high degree of professionalism also helps to demonstrate your value to the firm.

Employee Review Meetings

Many firms have regular employee review meetings, whether annually or at some other increment of time throughout a year. These are perfect opportunities to showcase the contributions which you have made and the future efforts which you have committed to pursuing. If your firm does not have regularly scheduled employee review meetings, it is reasonable to ask your manager to schedule one with you. In this case, the framing of the request for the discussion should be as a goals review meeting rather than a request for a compensation review. The discussion itself will take on the broader outlines of the employee's and the company's goals which then lends itself to the employee's goals for advancement, including compensation increases and promotion. By framing a discussion in terms of both the firm and the employee, the connections and synergies between the advancement of both can be highlighted. It is not a question of the employee simply "asking for" something, which is likely to be looked upon less favorably by an employer, but rather a discussion in which the performance of the individual and the firm are correlated and discussed. This is an opportunity to demonstrate the commitment of the employee both to their own professional development as well as to the firm's goals.

Demonstrate Worth through Self-Improvement

While proven job performance is an essential prerequisite for discussions of advancement, there are several other ways in which to distinguish oneself and set oneself up for success in compensation discussions. For aspiring engineers, the most straightforward way is to pursue licensure. This adds significant value to a firm's team. It also indicates that you are serious about your professional development and willing to take on the responsibilities that a professional title requires. Many firms even have stated policies related to specifically defined salary increases that an employee can expect upon receiving their licensure. Often, firms will compensate the employee for the fees associated with registering for the required licensure exams. While the road to licensure can seem long for those first entering the workplace out of college, it is important for aspiring engineers to begin the process of planning for the exams and documenting their work experience as required by the state in which the license is being pursued. While licensure can only be typically granted after passing the Principles and Practice of Engineering (PE) exam, it is also necessary to pass the Fundamentals of Engineering (FE) exam prior to the PE exam. Once a candidate passes the FE exam, a status of "Engineer in Training" (EIT) can be used. Becoming an EIT is a great short-term goal for engineering graduates. A good piece of advice is to use the passing of these exam milestones as stated goals during employee evaluation reviews and discussions. It shows that the employee is clearly interested in their advancement and willing to invest in themselves for their development. In turn, the firm is more likely to invest in employees who are investing in their own advancement since the advancement of the individual and that of the firm go hand in hand. The firm has already invested in its employees by hiring them, and it therefore has an interest in their advancement.

Professional Development Opportunities

Again, the best means of promotion and compensation advancement is to demonstrate professional development, which adds value to the firm and its work. Aside from the pursuit of licensure and overall quality of work on the job, engineers can distinguish themselves through many other means. This could take the outline of providing something unique and of value which other employees of the firm do not offer. For example, if there is a noticeable lack of quality CAD or BIM standards and the software skills of other employees seems to be somewhat lacking, then there could be an opportunity to take an initiative to help the firm improve in this regard by taking on an informal leadership role. There are ample resources available online for software training, and simply improving one's knowledge and offering assistance to other employees as a resource can provide a true value to the firm's work which is likely to be noticed by project managers. Even project managers who do not regularly use CAD or BIM software themselves can help demonstrate their value by improving their software knowledge so that they are familiar with the level of drafting or modeling effort associated with project work. This in turn could lead to better project scheduling and more accurate estimates for design efforts.

Adding Value

The idea of adding value to a firm can also more specifically relate to design knowledge, which can help to expand the versatility of a firm and aid in their pursuit of a wider variety of work and potential clients. For example, there may be a lack of employees with suitable knowledge of sustainable design principles and credentials. In this case, an engineer can demonstrate the potential value which could be brought to a firm by pursuing and achieving a credential such as LEED accreditation. This could help the firm gain the ability to pursue projects where LEED certification is required. Similarly, an engineer could pursue accreditation in WELL or attain an accreditation from the Construction Specification Institute such as CCS (Certified Construction Specifier) if specifications are an aspect of their work. Structural engineers could demonstrate their knowledge and expertise by passing the SE exam, which could allow an engineering firm to pursue work in states or project types where this credential may be required. Areas of specialization need not entail the pursuit of particular accreditations, though these do provide a means to demonstrate a proven level of knowledge in a particular area of interest.

Conclusion

In summary, for engineers seeking promotion or increased compensation, the best means of approaching the subject is often to demonstrate added value and the commitment to adding value. The pursuit of licensure and other accreditations is an excellent strategy, as they provide demonstrable and measurable levels of design knowledge and expertise. Such achievements may allow a firm to pursue additional types of work, which is a clear added value for an employee's firm. Specialization of expertise is an additional means of providing value which can distinguish you from others in the job market. By pursuing and demonstrating the added value which you bring to a firm, recognizing this value, and highlighting it during employee review meetings, you have the best chance of success in achieving recognition within a firm.

If you are wanting to boost your career with an engineering license, look no further than School of PE! For over 18 years, we have helped thousands of busy individuals pass their professional certification and licensure exams and look forward to helping you next! Sign up for a course today.

About the Author: Adam Castelli

Adam Castelli is a licensed architect and engineer currently practicing in the Pittsburgh area. He holds a master's degree in architecture from the University of Massachusetts Amherst and a bachelor's degree in civil engineering from Villanova University.

Fire Safety Issues Impacting Healthcare Projects

Fire protection systems and egress requirements are an important consideration for all types of building projects, but they are especially important for healthcare projects. In healthcare facilities, occupants of the building may be unable to egress the building without assistance from another person. Additionally, the importance of maintaining operations of a healthcare facility is often much greater than for other building occupancy types since patients rely on the continued functionality and operation of building systems for their health and safety. Therefore, project team members should understand the design requirements for the facility's fire protection systems, both active and passive, as well as egress requirements for this type of project. Proper ongoing maintenance of the building's fire protection systems and the education of staff for the prevention of fire hazards is also necessary once the building construction has been complete.

The blog covers:

1. Following Codes and Standards

2. Classifying Construction Types

3. Points to Keep in Mind

4. Egress Requirements

5. Group I Occupancies

6. Ambulatory Care Facilities

1. Following Codes and Standards

In designing fire protection systems, it is important to understand and follow the codes and standards which have been adopted in the particular jurisdiction in which the project is located. These may include the International Building Code, the International Fire Code, and the NFPA standards. When determining requirements related to life safety, it is necessary to determine the occupancy classification by code. The IBC, which is the model building code for most jurisdictions in the United States, provides a description of each occupancy type in Chapter 3 of the code. Depending on the specific uses with a particular healthcare project, the building occupancy may be determined. Some uses, such as outpatient offices where occupants are capable of self-preservation, may be classified as Business occupancy. Business classification also includes outpatient clinics as well as ambulatory care facilities (which have their own set of particular requirements within Chapter 4 of the code). Within the Institutional Group are sub-groups, specifically I-1, I-2, I-3, and I-4. Group I-1 includes uses such as 24-hour assisted living facilities, alcohol and drug centers, and social rehabilitation facilities. The individuals within these settings would need to be either capable of responding to an emergency on their own or with limited assistance. Group I-2, by contrast, includes 24-hour medical facilities where occupants are not capable of self-preservation during an emergency. This would include hospitals, nursing homes, and psychiatric hospitals. Groups I-3 and I-4 are less related to discussions of healthcare, being related to security facilities such as prisons and daycare facilities, respectively. It should be noted that NFPA classifications differ somewhat and should be reviewed when the NFPA standard must be followed. The IBC I-1 and I-2 occupancy classifications correspond with the NFPA occupancy classifications of Residential Board & Care and Healthcare, respectively.

2. Classifying Construction Types

In terms of allowable construction types, it should be noted that I-2 occupancy buildings are most typically built of non-combustible structures, that is to say Types I or II because I-2 buildings of the other construction types (even being sprinklered) would be limited to a single story in height. If a healthcare use were classified as Business, there would be significantly less restriction as far as building height and area is concerned.

3. Points to Keep in Mind

While an exhaustive study of the code requirements related to fire protection for healthcare is not possible in this discussion, there are a number of general points which are useful to keep in mind. For I-2 occupancies, which include hospitals, it is necessary that corridors, independent of any fire rating requirements that may apply, be built as smoke partitions. There are exceptions for certain types of spaces, but this is the general requirement. In addition to these smoke partitions, there are requirements to provide smoke barriers which divide the building into smoke compartments. A door which is located within a smoke barrier and connecting two parts of a corridor is required to have hold-opens such that they would automatically close in the event that smoke is detected. The IBC defines the requirements for determining these smoke compartments, which include area limitations and other factors. Each smoke compartment is also required by code to contain a refuge area. In addition to walls and doors which resist the passage of smoke, consideration must also be given to the horizontal assemblies which separate spaces so that these may also resist the passage of smoke as required by the code. An important consideration when designing for smoke compartments and separations is to ensure that any wall and floor penetrations (whether for cables, pipes, or other elements) within a barrier are sealed with appropriate firestopping. It is also important not to compromise the effectiveness of the barrier after the completion of construction with any subsequent work within the building.

4. Egress Requirements

It should be noted that there are also egress requirements specific to I-2 occupancies, which are listed in Chapter 4 of the IBC. Additionally, egress components such as stairways are often larger for I-2 occupancies because of the way that their widths are required to be calculated (i.e., multiplying the calculated occupant load by a larger factor than for other occupancy types - see Section 1005 of the IBC). Compared to Business occupancies, I-2 occupancies have a significantly lower threshold for the maximum number of occupants that can be in a space with only a single exit - 10 compared to 49. It is therefore common that a room of any size will have at least two exits. The travel distance to the exit access in an I-2 occupancy is also less than most other occupancy types, with 200 feet being the maximum distance allowed. In terms of egress, the need for lighting on emergency power should also be noted.

5. Group I Occupancies

Group I occupancies are required to have manual fire alarms, as well as automatic smoke detectors; both of which must connect to an occupant notification system. In terms of active fire protection systems, Group I occupancies are required by IBC to have an automatic sprinkler system. There are only a few exceptions to this requirement, and they relate to specific circumstances in I-1 and I-4 occupancies.

6. Ambulatory Care Facilities

Ambulatory care facilities can be understood as those which provide medical care to an individual for a period of time less than 24 hours, with these patients being considered incapable of self-preservation (whether because of a medical procedure or for other reasons). Like I-2 occupancies, ambulatory care facilities also have requirements for the use of smoke compartmentalization through smoke barriers. It is also required to separate spaces where occupants are incapable of self-preservation with fire partitions, which are to have a fire rating of at least 1 hour. Refuge areas must be provided within each smoke compartment of the building. Safety evacuation plans must also be developed for this project type so that an appropriate emergency response can be enacted for the facility. Further information on the requirements for the emergency response are found in the International Fire Code. Fire alarms and automatic sprinkler systems are also a necessity for ambulatory care facilities. In the NFPA, these types of facilities are classified as Ambulatory Health Care occupancy. NFPA has similar requirements to the IBC for this occupancy, but there are some differences, as the IBC treats this occupancy type as a subset of Business occupancy type (with special requirements), and the NFPA has a separate occupancy classification with its own set of requirements.

Conclusion

These are just some aspects of note for fire protection that should be considered in healthcare design projects. Familiarity with code requirements is especially important for this project type given both the importance of fire protection systems for these buildings as well as the level of detail and nuances of the codes and standards which must be understood for proper design of a building and its systems.

About the Author: Adam Castelli

Adam Castelli is a licensed architect and engineer currently practicing in the Pittsburgh area. He holds a master's degree in architecture from the University of Massachusetts Amherst and a bachelor's degree in civil engineering from Villanova University.

How to Prepare for the PE Exam After a Gap Period

A gap period can certainly develop between the Fundamentals of Engineering (FE) and Principles and Practice of Engineering (PE) exams. I have seen from co-workers and peers that it can be difficult to find time for PE exam studying and preparation when you become busy with family and other obligations. The FE exam is mostly focused on subjects that you learn in your engineering undergraduate curriculum; if you have been studying and doing your work in undergrad, then you will be well-prepared for the FE exam and probably will not need too much additional studying on your own time. This is why it is recommended to register for the FE exam while still an undergraduate or shortly after completing your undergraduate education so the exam topics are still fresh in your mind.

The blog covers:

1. PE vs. FE Exams

2. Investigate Exam Review Course Options

3. Obtain Most Recent Reference Materials

4. Exam Content Changes

5. Review NCEES Exam Guidelines

6. Steps: How to Prepare for the PE Exam (After a Gap Period)

1. PE vs. FE Exams

But the PE exam is a much more practical exam compared to your FE undergrad subjects. Industry experience will help you to gain exposure to some of the different topics, but you will need additional preparation on your own. I passed the exam in Pennsylvania (PA), and at the time, you needed four (4) years minimum working experience before submitting your application to sit for the exam to the State Board. In those four years, I completed my graduate school for business and was naturally removed from engineering undergrad, so I was certainly feeling the gap period when I revisited past textbooks. I tried self-studying early on but quickly found myself overwhelmed and was lacking defined direction that would be needed to pass the PE exam.

2. Investigate Exam Review Course Options

You may want to spend a little time with undergraduate and graduate engineering reference materials as a refresher, but some information may be outdated after an extended gap period. I enjoyed my business graduate courses, but these were separate from PE exam topics; my only continued exposure to engineering was industry, so I needed help with my preparation. School of PE offers excellent online review courses with sections that correlate with National Council of Examiners for Engineering and Surveying (NCEES) PE exam topics. A friend had first recommended School of PE to me, and it really was the turning point in my studying habits. I gained a much better sense of the types of questions that would appear on the PE exam, and from that, I also gained more confidence with my ability to earn a passing result. Before passing the FE exam, I attended a weekend review class that helped with my preparation. But the online classes offered by School of PE provided me with both detailed notes and recorded sessions so I could study at my own pace without concern about slowing down the review class. And since I was in my own gap period, I needed to go at a slower pace.

3. Obtain Most Recent Reference Materials

In addition to an online review course (I would recommend School of PE!), you should investigate purchasing copies of the most recent reference materials. Either from NCEES, School of PE, or another credible source, other resources will help you better understand the PE Reference Handbook. When I took the PE Mechanical (Thermal and Fluid Systems) exam, you were permitted to bring your own reference materials on exam day. I know that has changed in recent years, and that for many PE disciplines, only the PE Reference Handbook is permitted during the exam. However, other studying sources may help you better understand the PE Reference Handbook. When preparing after a gap period, you certainly want to review multiple resources since there is overlap with different exam topics and multiple resources can help to better bridge the gap period.

4. Exam Content Changes

NCEES conducts an exam content review every 6-8 years, so if your gap period has exceeded this timeframe, you will probably need to start fresh on your PE exam preparation (e.g., if you last attempted the PE exam several years ago). The good news is you do not need to start over from the beginning with trying to relearn your engineering undergraduate curriculum! But you may need to teach yourself some new topics (this is where the review course becomes handy). A review course can help narrow your scope so you can focus on the most relevant topics needed to pass the exam. Most PE exams will be mostly multiple-choice questions, and you do not need to provide any justification for your answers. The PE exam is a more practical exam compared to the FE exam, but there is still a good level of textbook knowledge that you will need to achieve a passing score. The PE exam itself started in the 1960s and has evolved over the years, so be sure to keep yourself updated with NCEES standards. Just to give you an idea, one of my PE references sat for the exam in the 1980s, and back then it was an open-ended exam where you needed to show your work, so PE licensure has certainly undergone different variations.

5. Review NCEES Exam Guidelines

You should start with reviewing NCEES exam guidelines on their website; you can also check School of PE for examination info too. If you already applied for the PE exam, you should follow-up with your State Board to ensure that your application and references are still valid. Once you pass the PE exam and attain professional licensure, you only need to worry about completing your continuing education requirements (most states in the United States require approximately 24 credit hours). I would also recommend discussing with other licensed PE co-workers and colleagues their experience with exam preparation. They may have tips and advice that could help you with the application process and/or studying if they recently passed the PE exam. Things have recently come full circle for me; the other day, I was discussing the application process with a co-worker who is preparing for the PE exam this year.

And now I will present to you my step-by-step "unofficial" guide to preparing for the PE exam (after a gap period).

6. Steps: How to Prepare for the PE Exam (After a Gap Period)

1) Review NCEES format.

2) Review existing reference materials as background.

3) Discuss which exam to take with co-workers (Mechanical, Chemical, etc.); gain advice and tips on the exam application process-my undergraduate engineering degree was in Chemical Engineering, but co-workers recommended the PE Mechanical: Thermal and Fluids Systems exam for more workplace relevance (and they were correct!).

4) Apply for PE exam and/or update registration; if there has been a long gap period, explain to the State Board your situation and see if they can provide an update on your application status. You may also be able to check your online account if it is still active.

5) Once you have confirmed approval to sit for the PE exam, identify your preferred exam date. Most PE exams are computer-based testing (CBT), so you can take the exam just about any time, year-round.

6) Sign-up for an online review course. The PE Mechanical review course that I completed through School of PE was instrumental towards helping me pass the PE exam on the first try.

7) Study! (Review course, practice questions, practice exams, etc.); I would recommend reviewing recent exam materials since NCEES updates the exam format every 6-8 years. It is highly unlikely that the exam administration would include irrelevant or outdated exam questions. If you encounter questions that seem to deviate from the exam format or are from over five years ago, these types of questions probably will not appear on the PE exam.

8) Plan how you will celebrate once you pass the exam. I bought gift cards for my references to show my appreciation for their reference endorsement and advice on recommending the PE Mechanical Thermal exam.

9) Above all else, put yourself in the mindset that you will pass; be optimistic-you can do this! Remember, there is no limit to how many times you can take the PE exam, so passing is a matter of when not if-again, keep that positive mindset!

If you're preparing for your PE exam, consider a partnership with School of PE. Our subject-matter expert instructors and comprehensive course materials provide what you need to succeed on exam day! Register now.

About the Author: Gregory Nicosia

Gregory Nicosia, PE is an engineer who has been practicing in the industry for eight years. His background includes natural gas, utilities, mechanical, and civil engineering. He earned his chemical engineering undergraduate degree at Drexel University (2014) and master's in business administration (MBA) from Penn State Harrisburg (2018). He received his EIT designation in 2014 and PE license in 2018. Mr. Nicosia firmly believes in continuing to grow his skillset to become a more well-rounded engineer and adapt to an ever-changing world.

9 Facts You Never Knew About Flammability

Health, Safety, and Environment (HSE) is a topic on the Fundamentals of Engineering (FE) Chemical exam (5-8 questions). Although the number of flammability questions that you will encounter on the FE exam is limited, flammability has always been an interesting subject to me. There is a science to computing flammability values and evaluating the likelihood of fire and ignition in a process or workplace environment. There are six (6) different classes of fires (A, B, C, D, F, Electrical), so it is a topic that should be explored in further detail, not just to pass the FE Chemical exam. The National Fire Protection Association (NFPA) Hazard Rating Diamond (NFPA 704: Standard System for the Identification of the Hazards of Materials for Emergency Response) has the red section focused on flammability; the NFPA diamond is also included in the FE Reference Handbook (v 10.0.1, p. 14).

In this blog,

1. Class A, B, and C

2. Class D

3. Flammability Measures

4. Transporting Flammable Materials

5. Upper and Lower Limits

6. Combustible Gas Indicators

7. Heavier Hydrocarbons

8. Propane

9. Carbon Monoxide

1. Class A, B, and C

Class A refers to organic combustible materials, such as paper and wood. Trees are obviously comprised of wood, but forest fires have their own sub-categories. Class B refers to flammable liquids like fuel oil (gasoline/petrol). Gasoline is the US English term whereas petrol is the British English term. The United States and Latin countries consider fuel oil as gasoline while Europe and Asian countries call fuel oil petrol. It should be noted that gasoline and petrol are one in the same, but terminology depends on location. Class C is for flammable gases such as natural gas (methane) and propane. In layman's terms, natural gas and methane are essentially the same substance. However, the actual difference is that natural gas contains trace amounts of ethane. Due to this, the molecular weight of natural gas (17 g/mol) is slightly higher than methane (16 g/mol). Ethane (two carbon atoms) is a slightly heavier hydrocarbon compared to methane (one carbon atom), hence the slightly greater weight.

2. Class D

Class D refers to flammable metals such as lithium. Lithium-ion batteries are a rechargeable battery technology that is growing in the industry. But they are not safe at excessively high temperatures and are vulnerable to catching fire. Class F is for deep fat fryers (fats, cooking oil). Class F is sometimes considered to be a sub-class of Class B (liquid) and Class C (gas) fires, but Class F is more applicable to kitchen fires that can occur at dangerously high temperatures. Class Electrical is, of course, for electrical equipment (the letter "E" is not actually used); electrical fires can fall under any of the other five (5) classes since electrical current (e.g., spark) is causing the ignition.

3. Flammability Measures

Section 5 of a substance's Material Safety Data Sheet/Safety Data Sheet (MSDS/SDS) lists fire-fighting measures (FE Reference Handbook, v 10.0.1, p. 18). The FE Reference Handbook also describes flammability limits (v 10.0.1, p. 19-20). The Fire Triangle consists of the three (3) components needed to start a fire and continue burning; they are heat, fuel, and an oxidizing agent (oxygen). Flash Point refers to the lowest temperature that material vapor will ignite if exposed to an ignition source. This is why liquids with a flash point below 100^° F (38^° C) are flagged as flammable by both the NFPA and United States Department of Transportation (USDOT). A material with a lower flash point material is more volatile and dangerous if near ignition sources. Room temperature (68-74^° F) is well below the 100^° F threshold, so materials at room temperature are generally non-flammable since it is unlikely that a material would catch fire under standard temperature conditions.

4. Transporting Flammable Materials

The National Transportation Safety Board (NTSB) is the U.S. government agency that oversees the investigation of transport accidents and incidents. This coincides with the USDOT since both government agencies focus on transportation. Materials such as liquefied natural gas (LNG) and liquefied petroleum gas (LPG) require oversight since they are often transported by ground vehicles. It is crucial to identify any materials that may be volatile at temperatures below 100^° F; vehicular accidents can lead to devastating fires and explosions that may cause human fatalities and damage to roads, bridges, and other highway infrastructure. Flash point is usually seen in laboratory environments, but you should certainly be mindful if you are driving near trucks and tractor trailers that are transporting volatile fuels.

5. Upper and Lower Limits

Flammability applies to all material states, including solids, liquids, and gases (vapor). Material flammability can also be defined by the upper and lower limits. The limits are lower flammability limit (LFL) and upper flammability limit (UFL); these limits are also known as lower explosive limit (LEL) and upper explosive limit (UEL). Both "flammability" and "explosive" are interchangeable terms when discussing the limits. The limits apply to vapor-air mixtures (volume % in air); if the concentration is above the UEL, then the mixture is too rich to burn; if the concentration is below the LEL, then the mixture is too lean to burn. The in-between range is ignitable and should be carefully monitored if these conditions occur.

6. Combustible Gas Indicators

A combustible gas indicator (CGI) is an instrument that can be used to measure vapor-air mixture concentrations in a room or area. CGIs can be calibrated for different gases; methane (natural gas) is the most common since many homes and businesses utilize natural gas for heating and cooking appliances. A CGI is a good tool, and I would recommend purchasing one for your own household since it can function like a smoke detector and carbon monoxide (CO) detector. While propane has a lower concentration range compared to natural gas, propane still poses a more dangerous explosion risk. In my opinion, a lower LEL (2.1% for propane) is also more hazardous since you do not need a large concentration to enter the explosive range. You are more likely to cross beyond the LEL range than surpass the UEL range; propane explosions and fatalities have occurred at homes and businesses due to an accidental leak that did not have a large concentration needed to ignite.

7. Heavier Hydrocarbons

It should also be noted that heavier hydrocarbons (e.g., butane, pentane, octane) have lower LEL values; as a rule of thumb, heavier hydrocarbons (more carbon atoms) have decreasing LEL values. UEL values decrease with heavier hydrocarbons too. But I would more closely study the LEL values for different volatile materials since those are more probable. For example, gasoline is a common fuel source and has a low LEL value, so it is generally considered flammable. Heat and other ignition sources should be avoided at gas stations and other fuel areas.

8. Propane

Propane is denser than air, so it does not rise to vent like natural gas in the case of a gas leak. Because propane settles, it creates a more hazardous environment compared to natural gas, so natural gas is more widely used for utility appliances (but I think propane having a lower LEL value is another reason natural gas is more favorable). Since propane (C3H8) is also a hydrocarbon, it is non-polar; you cannot spray water to disperse a propane gas release like you could with a more polar substance like ammonia (NH3). Polarity is due to differences in electronegativities and is a periodic table trend. Fluorine is the most electronegative element. Non-metals (Right Side) are more electronegative whereas metals (Left Side) are electropositive and therefore have lower electronegativities; this creates the difference in polarity. Ionic compounds such as table salt (NaCl) are perfectly polar and dissolve readily in water (H2O). You can also refer to the periodic table in the FE Reference Handbook (v 10.0.1, p. 88).

9. Carbon Monoxide

Carbon monoxide (CO) is slightly less dense than air. However, it is not enough to rise quickly, so you must evacuate in the case of a spike in CO concentration that would alert a CO detector. The CO concentration will displace the oxygen in your body faster than it can rise to vent outside; this is how death by asphyxiation occurs. You should become more familiar with the topic of flammability and understand the science, not just for your engineering career, but also as personal advice. I described many different household materials (e.g., natural gas, propane, cooking oil, gasoline) that are used in everyday life to help you stay safe and educate others. There are always ongoing HSE issues in the industry; you can read more online on the Occupational Safety and Health Administration (OSHA) website and check back with School of PE for more HSE blog posts.

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About the Author: Gregory Nicosia

Gregory Nicosia, PE is an engineer who has been practicing in the industry for eight years. His background includes natural gas, utilities, mechanical, and civil engineering. He earned his chemical engineering undergraduate degree at Drexel University (2014) and master's in business administration (MBA) from Penn State Harrisburg (2018). He received his EIT designation in 2014 and PE license in 2018. Mr. Nicosia firmly believes in continuing to grow his skillset to become a more well-rounded engineer and adapt to an ever-changing world.