Electricity: Part One

The first in an energetic series of posts on what electricity is and how it’s used, generated and distributed.

We don’t consume electricity; we use energy; transforming it into different forms to make our world brighter, warmer (or cooler) and make work easier. We strive to conserve and efficiently use energy, but in the end, we really only change energy from one form to another. Energy never goes away; it just finds another job to do.

If electricity is only the transportation system for the energy we use, then what is electricity and how does it work?

Although the Money Pit is one of my favorite movies, here is an example of how electricity does NOT behave.


In the simplest of terms, electrical current is the excitement and flow of electrons. To understand what that means, we need to start with the most basic building block of all matter: the atom. All matter is made from a combination of atoms (either of one kind or multiple). Any substance that cannot be separated into a simpler substance by chemical means is considered an element. All known elements are cataloged within the ‘Periodic Table of Elements’, a table that has stressed out generations of high school chemistry students. The periodic table of elements describes the individual atomic characteristics of each element, and knowing those characteristics gives us more insight into how they all behave with each other. It’s not unlike knowing the personality types of your friends and co-workers.

The Periodic Table of Elements
Each atom is composed of three basic particles: the electron, proton and neutron. Protons and Neutrons are located in the atom’s nucleus, with the electrons orbiting around in a series of concentric “shells”. Science has uncovered even smaller particles that make up and hold together each atom’s structure, but for our purposes it is the negatively charged electrons (or their absence) that hold the secrets of electricity.

Early scientists such as a Frenchman by the name of Charles Dufay realized that certain materials became attracted to certain objects, but were repelled by others. The forces of attraction and repulsion are described as either a positive or negative charge. As neutrons have no charge, each atom’s nucleus has a net positive charge. As Paula Abdul’s 1988 hit described, “We come together, cuz opposites attract”. Objects with similar charges are repelled from each other, and those with opposite charges are attracted to each other.

At this point, I know that many readers are beginning to have flashbacks to early childhood science class and are wondering, “Where is he going with this? It’s about as exciting as watching paint dry.”

Excitement is exactly what electricity is all about. The outer shell (known as valance electrons) of each atom contains between one and eight electrons. Each atom seeks stability by filling up its outer shell with all eight; a nice calm retirement of sorts. Some atoms like the noble gases Argon and Xenon start out with their outer shells full; they’re calm, unexciting and don’t over-react. Other elements such as gold, silver and copper have only one electron in their outer shell and are more than willing to dance the night away in an attempt to lose that electron and settle down into a more stable existence (a very unlikely outcome given their propensity to getting over-excited). The following animation shows a copper atom, with only one electron in its outer shell. The nucleus, comprised of 39 neutrons and 39 protons is shown as a single sphere at the center (To be honest, I didn’t feel like modeling all 78 spheres in the nucleus; my obsessive nature does have its limits).

Atom Model Moving - 25fps 640x480
Copper (CU),  Animation © DFD Architects, Inc.
At the risk of perpetuating stereotypes, we can group elements and materials by how they behave when excited. In terms of electricity, elements and materials (combinations of elements) can be put into three groups:

Conductors, Insulators and Semi-conductors.

Elements with 3 or less electrons in their outer shells are generally conductors (although the exact number of electrons does not always determine which elements are the best conductors). Because they have lots of empty room in that outer orbit, they are less stable and more likely to lose their remaining electrons when bumped around (The bump theory is a commonly held explanation for how electrons are passed from one atom to another). Insulating materials such as wood, glass and rubber are combinations of elements that fill their outer shells by sharing their electrons with other elements. These materials are composed of elements such as Carbon, Oxygen, Nitrogen and Hydrogen. Alone these elements are not very stable, but combined they have found comfort and stability. Selective elements such as Silicon and Germanium are termed semi-conductors, and have 4 electrons in their outer shell. With a little encouragement these elements can be persuaded to lose an electron or two and become negatively charged. These materials have become indispensable in the development of solid-state circuitry and computers in general.

That bumping around of electrons in a conductor is precisely where the transfer of energy via electricity happens. Like billiard balls on a pool table, when the energy is introduced at one end (the player hitting the cue ball), energy is transferred from one ball to the next. Not all energy is passed from one ball to the next however. In billiards, you’d hear the sound of balls hitting, and if measured, you could see the heat generated by the instantaneous collision. With electrons in a conductor, that energy release may be heat, light and almost always a magnetic field.

Magnets? I thought we were discussing electricity?

Everyone has played with magnets as a kid (or adult). Those of us old enough to remember iron filing and magnet toys such as “Wooly Willy”, have seen what a magnetic field actually looks like. The following image shows a magnet with a negative and positive end (or “pole”) often termed a North and South pole.  The iron filings align with the resultant magnetic lines of force (or ‘flux’). No we are not going to enter into a discussion of whether Santa Claus or penguins reside on either pole (maybe in a later post).

Patterns of magnetic flux (iron filings and a magnet)
Magnetic fields, created by electrons flowing through a conductive material, are precisely what enables a generator or alternator to initiate the flow of electricity, and appliances such as motors to use that flow of electromagnetic energy to create mechanical movement.

This whole discussion can seem very theoretical, given that we can only see the results of what magnetics and electricity can do. So how do we measure that flow of energy across a conductor?

Before we talk about measuring electricity, it’s important to know why it flows at all. Electromagnetic energy will not flow through anything unless it has somewhere to go. OK, time for a few metaphors:

Everyone is familiar with water pipes in their house, or at least knows that water comes from somewhere when the faucet is turned on. Why doesn’t water flow continuously from the kitchen faucet? It doesn’t flow all the time, because without an open outlet (someone using that water), it will just sit nice and quiet in the pipe. Open a faucet, and the water begins to flow. Break a pipe or create a leak, and water will flow to places you don’t want it to. Electricity is very similar. Without a load, or something to use that energy, there is no need for the electrons to bump into each other and pass along their energy. Unlike the water in our pipes however, electricity wants to flow from a positively charged source to negatively charged one (this is according to popular theory, but let’s leave theory out of this for the moment as it gives me a headache). More often than not, that flow may be from a positive terminal of battery to the negative one, or a positive source to the earth itself (such as in a building’s electrical system). Without a complete “circuit” to follow, the electrons will have nowhere to go, and the flow of electricity will stop. If you provide a complete path for the electricity to follow, then it will happily oblige. There is a reason that they refer to the Formula One race car events as a circuit. If the road was open on both ends and didn’t connect, it would be a very short race. Yes, I’m aware that would be considered drag racing; metaphors have their limits.

Measuring the energy carried by electricity

Before I lose anyone, let’s talk about volts, amps and watts. In my next post we’ll talk about AC/DC, and by that I’m referring to Alternating and Direct Current, not the 80’s band from Australia. I’m sure everyone has heard the phrase, “It’s not the voltage you have to worry about; it’s the amps”. While partially true; why? It has to do with force and potential energy.

If electricity is the flow of electrons, then measuring energy carried by electricity must involve electrons right? Well, unless you have an incredibly powerful microscope, and someone who is really fast at counting, we’re going to need a standard to measure against for counting electrons. Here we learn about Charles-Augustin de Coulomb, a French physicist whom the standard imperial measurement of charge was named after (his story would be another post). One coulomb is equivalent to the charge of 6.242 X 1018 electrons. That’s a lot of electrons. In obnoxiously large numeric terms, that’s six quintrillion, two hundred and forty-two quadrillion electrons. That should be easy enough to put into an Excel spreadsheet, right? Well, instead of counting every electron over a period of time, how about we just divide the total number of electrons by a nice big number like a coulomb? Well it so happens that the volume of one coulomb per second is referred to as an ampere. Whoa! Amps are actually related to something physical?! Don’t get too excited, we’re still talking about theoretically numbers and some basic assumptions, but at least we have somewhere to start.

So if one ampere (normally referred to as an Amp), is a volume of electrons over time, then we should be able to measure the energy those electrons are moving with them right? Not so fast. Volume (or size) is one side of the equation, but we’re missing the other half. We need a push. We need that potential energy to work with.

Caution: Dangerous metaphors ahead.

What is potential energy? If your house was on fire, and you asked for a water hose; I’m sure you’d be rather upset if someone walked up with a garden hose connected to a hand pump. You’d prefer a fire hose connected to a rather large fire truck I’m sure. Why? The difference is in potential energy. Only so much water can flow through a garden hose. Given a bigger and stronger hose, you could push more water through it. Water is normally measured in volume over time; commonly gallons per minute. A garden hose can easily provide 10 gallons per minute, but so can a fire hose. The fire hose however has the potential to provide much, much more water if it is needed (which it usually is). Here’s another example: Let’s say you are sitting quietly at the base of ten-foot cliff, and a rock is perched very precariously above you. It’s not moving, but given a bit of a push, it could fall at any time. If that rock weighed a few grams, the potential for harm to your pretty head is minimal. If that rock weighed 10,000 lbs., then the potential for harm would be rather substantial. Unless it’s actually falling, both rocks are harmless. The 5-ton rock however has a much larger potential energy (it COULD exert a much bigger force).

Since electricity transmits energy, we need to know the volume of energy over time, but we also need to know the level of force with which it is delivered. In terms of water in a pipe, this potential energy is referred to as pressure (in pounds per square inch, or PSI). In the flow of electrons, this potential energy or pressure is called voltage. One Volt is the potential energy it would take to drive one amp of current against a given load (we’ll talk about loads in the next post).

Now we’ve brought energy and force into the equation. Flowing electrons mean nothing if they bump off a conductor one at a time, but if they flow in great numbers (along with their accompanying magnetic fields) with a large amount of force, then now we have energy we can use. With both volume and force, we can move almost anything.

So how do we measure the power or work that electricity provides? Enter the “Watt”. One watt is equal to one volt of potential energy times one ampere of flow. The watt is a measure of the real power that pushes, heats or illuminates. For comparisons, this would be similar to horsepower (735.5 watts), or foot-pounds of force per second (1.355 watts).

In electrical terms, the watt, is proportionately equal to the volts (the potential energy) times the amps (the volume of flow). 1 Watt = 1 Volt x 1 Amp. I know. Some of you just went… uh, duh, but the majority of people just had that little 13 watt LED light bulb (equivalent to a 60 watt incandescent bulb) go off in their head and said, “Oohhhh, I get it.”. You’re welcome.

So let’s stop there for the moment, because unless you’re an electrical engineer or a geek like me, you may need a week to recover from reading this post.

Next time we’ll talk about Direct Current, Alternating Current, Single-Phase Power, Three-Phase Power, generators and transformers. I know, you’ll have a tough time waiting, but it should be worth it.

In the meantime, here is your moment of Zen (Yes, I’m a fan of the Daily Show on Comedy Central):



I promise not to beg, but I would really welcome any comments; both good and bad (but constructive). The more feedback I get; the better my posts can be. Thanks!!


The Money Pit, Copyright NBC Universal, 1986

A Christmas Story, Copyright Warner Bros. Home Entertainment, 1983

Magnet and Periodic Table images are public domain and are available on https://commons.wikimedia.org

Fire burns, but let’s be clear on what that means

Man is the only creature that dares to light a fire and live with it. The reason? Because he alone has learned how to put it out. – Henry Jackson Van Dyke, Jr.

Humans have learned to utilize fire’s power and enjoy its beauty and warmth, but yet we are still learning to protect ourselves from its destructive nature. In order to improve, there must be meaningful conversations and collaboration between those who study, design for, live with and fight against fire. To do so, they must all speak the same language. The English language has so many different words for concepts and ideas that are nearly identical, yet each conveys slightly different emotions, details or opinions depending on context and intent. The simple fact that each word has specific meanings allows you to (hopefully) understand what I have written here. When lives are at stake, there is no room for confusion or arguments resulting from improper use of a simple word. Knowing the exact and agreed upon definitions to certain terms used throughout the various codes and standards is also often the biggest stumbling block to understanding key concepts. The following terms are not interchangeable, and it is therefore critical that everyone understands them.

Flammable, Combustible, Non-Combustible, and Fire-Resistance

All four of these are common throughout dozens of codes and standards; the term “combustible” is used in some form almost 300 times in the IBC alone. They are also used in everyday news reports and on thousands of product labels. Once you have the real definition, you’ll be amazed at how often they are mis-used and actually lead to incorrect assumptions.

The International Building Code (IBC) and NFPA 101 actually avoid defining three of these terms in a simple sentence or paragraph because in order to be classified under one term or another, the material must be tested in a recognized manner. If the definition of what combustible meant was summarized by a highly interpretable paragraph, nobody would ever fully agree on whether something was or was not combustible. Basing a definition on whether something has passed a consistent and widely accepted set of criteria and even testing helps to reduce interpretation errors.

The first two are often used interchangeably, but should not be:

Flammable versus Combustible

Here are some official definitions. Note that I’m including the definition of noncombustible because combustible is defined as anything that cannot be called noncombustible. Yes, I know the thought, “Well, Duh…” entered your head, but it’s actually an important point.

Flammable: capable of being easily ignited and of burning quickly – Merriam-Webster.com (1)

Flammable Material: A material capable of being readily ignited from common sources of heat or at a temperature of 600°F or less. – 2015 IBC

Combustible Material: A material that, in the form in which it is used and under the conditions anticipated, will ignite and burn; a material that does not meet the definition of noncombustible or limited- combustible. – 2012 NFPA 101

Noncombustible: A material that complies with any of the following shall be considered a noncombustible material:

(1)*  A material that, in the form in which it is used and under the conditions anticipated, will not ignite, burn, support combustion, or release flammable vapors when subjected to fire or heat

(2)  A material that is reported as passing ASTM E 136, Standard Test Method for Behavior of Materials in a Vertical Tube Furnace at 750 Degrees – 2012 NFPA 101

There are three key differences in these terms:

  • Flammable material ignites from common heat sources or at a temperature less than (or equal to) 600°F. Combustible material is ANYTHING that ignites, burns, supports combustion, etc… at any temperature or from any fire.
  • The term flammable is most commonly used to refer to fabrics, furnishings, decorations, clothing, and other such non-building related components. Combustible is more often used to describe a building material or finish that will burn.
  • Combustible materials are defined as those that would FAIL the ASTM E 136 test.

Using these definitions: All flammable materials are also combustible. Combustible materials are not always flammable. Whoa… what did he just say? Let me give an example:

A product that has been a big part of recent headlines is the metal composite material (MCM, or ACM) Reynobond PE®. It is composed of aluminum sheets (a non-combustible material) with a polyethylene foam core. Polyethylene foam ignites at a temperature of 340℃ (644℉) (2). Because the foam ignites at all it is considered combustible. The panels however would not be considered flammable as the aluminum skin does not burn (keeping flame away from the inner core under “common sources of heat”), and below 600℉; the foam core does not ignite. In this particular case, the material is NOT flammable by definition. It IS combustible. I would encourage you to read my first blog post for more discussion on the Grenfell Tower fire.

Ok, so flammable and combustible are different, but it’s just semantics right?

Noncombustible and Fire-Resistance

Let’s look at the other two terms: Noncombustible and Fire-Resistance / resistive. These unfortunately are used in similar ways, but do NOT have the same meaning.

Noncombustible: A material that complies with any of the following shall be considered a noncombustible material:

(1)*  A material that, in the form in which it is used and under the conditions anticipated, will not ignite, burn, support combustion, or release flammable vapors when subjected to fire or heat

(2)  A material that is reported as passing ASTM E 136, Standard Test Method for Behavior of Materials in a Vertical Tube Furnace at 750 Degrees C

– 2012 NFPA 101

Fire-Resistance Rating: The period of time a building element, component or assembly maintains the ability to confine a fire, continues to perform a given structural function, or both, as determined by the tests, or the methods based on tests, prescribed in Section 703. (Those tests are ASTM E 119 or ANSI/UL 263) – 2015 IBC

A material that will not ignite or burn in any way, such as steel, is considered non-combustible. Steel on its own however, does not maintain its structural strength when subjected to high heat, and therefore has a very low (if any) fire-resistance. It may sound hard to believe, but a heavy timber column (say 12 inches x 12 inches in dimension) will remain structurally sound much longer in a fire than the same size steel column.  Another common example is cementitious siding (known by the brand name HARDIEPANEL®). This product is non-combustible (3), but does little to confine a fire as it can quickly fall apart when subjected to an actual fire reaching more than 1,500℉, and therefore has little to no fire-resistance.

If you want to protect and separate the occupants of a building from a fire, you need materials and systems that are fire-resistive. They actually remain in place and hold together long enough to keep the fire away or hold the building up. There are fire-resistive systems constructed of non-combustible materials and just as many that are made with combustible materials.

Fire-resistance is not an issue of will it burn or not (combustible versus noncombustible); it is determined by how long a material or system will resist the fire and protect a building’s occupants.

It’s impossible to design, construct, or correctly maintain a building that protects its occupants if these terms are used incorrectly; besides, you’ll sound smarter using the right one.

More Information:

There are plenty of other terms related to building codes that are mis-used or mixed up that I know we’ll discuss later.

For additional information on fire-resistive properties of Aluminum Composite Materials (ACM) and the fire-resistant testing procedure ASTM E 119, please take a look at the following videos from Alucobond® and National Gypsum®.




  1. https://www.merriam-webster.com/dictionary/flammable
  2. Q & A on Fire and Fire Prevention of Rigid Polyurethane Foam, May 2009, Translation into English by JUII Fire Safety Committee from revised Japanese text, December 2011, Japan Urethane Industry Institute (JUII). http://www.urethane-jp.org/topics/doc/Q&A_on_Fire_and_Fire_Prevention_of_Rigid_Polyurethane_Foam_REV1.pdf
  3. ICC-ES Report, ESR-1844, HARDIEPANEL® (PREVAILTM, CEMPANEL®) SIDING, HARDIFLEX® SIDING AND HARDITEX® BASEBOARD https://www.jameshardie.com/JamesHardieMainSite/media/Site-Documents/TechnicalDocuments/Reports/ESR-1844.pdf

Codes 101

Understanding the intricacies of building and life safety codes is simply a matter of learning why they exist, how they are used, and where to get started.

The codes and standards used to regulate the construction, maintenance and general use of nearly every structure in the United States can seem confusing, frustrating and even occasionally contrary to common sense. Like so many other aspects of modern life, specific skills and knowledge are needed when dealing with highly specialized subjects. It isn’t reasonable to expect everyone to amass the in-depth knowledge of biology, anatomy and chemistry needed to be a doctor; nor is it possible for everyone to have the skills and talent needed to compose, conduct or play the violin in a classical symphony. While music may require more talent than architecture and construction (in my opinion), they both require practice and a lot of learning. Understanding the intricacies of building and life safety codes is simply a matter of learning why they exist, how they are used, and where to get started. Although seemingly complex, once you have the basic concepts down, the code is something akin to the “Choose Your Own Adventure” book series produced by Bantam Books in the 1980’s and 1990’s. Given one set of decisions, the codes send you in a specific direction for requirements and additional choices to make. Maybe there was a reason I enjoyed those stories as a kid, because as a self-described Code Geek, I find it rewarding to track down code requirements and learn new things everyday (sometimes with negative results, but often with positive ones). Codes are critical to protecting the health, safety and welfare of the public through consistency and minimum levels of quality and protection. The codes were not created in a vacuum by politicians trying to increase tax revenue or regulate just for the sake of control. Every code and standard in use today began with individuals and groups getting together when agreed upon standards were needed; often in response to tragedies and failures that could have been avoided. The codes exist because of one reason; people caring for the safety of others.

What is a code, and who can enforce one?

The building and life safety codes today are published documents, rule books if you will, that provide guidance and limitations on a wide variety of topics and disciplines. The codes are generally written by both non-profit and private groups, and then published for use. The codes themselves are only words on paper until they are actually adopted by a jurisdiction that has the legal right to do so (such authority is typically given through federal, state, county or local government laws).

This is the single most important concept to understand: A code must be adopted by a governing body such as a federal, state, county, city or other such jurisdictional entity in order to be considered actual law.

Once adopted, that Authority Having Jurisdiction (AHJ), is now responsible for enforcing the provisions and requirements of the code. AHJ’s may also include taxing entities like water and utility districts, emergency service districts (fire and police services) and health departments. Once adopted, the code is the law of that jurisdiction and they are now responsible for not just enforcing it, but also the interpretation and even amending of it to suit their specific needs.

Most jurisdictions will also rename it to become their code. The City of Dallas, Texas, has adopted the 2015 edition of the International Building Code, and in doing so renamed it as the “Dallas Building Code”. (1) Technically under Texas state law, and many other states as well, a jurisdiction could write their own code from scratch so long as it meets the minimum safety standards as a published code. I’m not aware of any municipality willing to spend the time and money necessary to write their own code in lieu of starting with a nationally published one. In the end, although originally published by various organizations, those groups are not responsible for its enforcement, and do not have any authority to officially interpret the code; only the AHJ has that authority. Most AHJ’s will look to the original publisher for guidance, but it is the AHJ that makes any decisions needed. The key idea to remember is once adopted, it is their code.

An abbreviated history of US Life Safety Codes:

Prior to the 1890’s, no formal codes, standards or even guidelines existed to maintain consistency among the early pioneers and inventors of two burgeoning industries; Fire Sprinkler Systems and Electrical Systems. Following the invention and patenting of the first sprinkler head by Henry S. Parmelee of New Haven, Connecticut in 1874, and significant concerns surrounding electrical installations at the Chicago World’s fair and across the United States in 1893, interested groups began to meet and discuss the need for standards and rules for such systems. As expected, any early attempt at consolidating personal opinions and solutions would be unlikely, and at the end of 1895, there were five distinct electrical codes in the United States and no defined standards for sprinkler systems.

In 1896, and again in 1897, several national organizations met in New York in an attempt to consolidate the various standards, and in 1897, the “Joint Conference of Electrical and Allied Interests” established the “National Electrical Code of 1897” which was adopted and issued by the National Board of Fire Underwriters. This would eventually become NFPA 70, the National Electrical Code (NEC)

Also in 1896, a separate meeting was held in New York City by parties trying to consolidate standards for fire sprinklers; their release of sprinkler installation rules entitled, “Report of Committee on Automatic Sprinkler Protection” eventually became “NFPA 13”.

In November of 1896, a new organization known as the “National Fire Protection Association” (NFPA) was formed from many of the same members previously involved. The long history of NFPA and its members is a tribute to the thousands of individuals who have volunteered their time to establish rules and standards. (2)

The NFPA would then continue to play a large part in the development of new safety standards. As is the case with many codes, tragedies such as the Triangle Shirtwaist Fire on March 25, 1911 in which 147 people perished led to the development of the “Building Exits Code”, which would later become NFPA 101, The Life Safety Code. Although it existed at the time, the Building Exits Code was widely ignored, and further tragedies occurred such as the 1942 Cocoanut Grove Fire in Boston, Massachusetts in which 492 people died, and the 1958 fire at the Our Lady of Angels School in Chicago in which 90 students and 3 nuns died. Established criteria in the Building Exits Code prohibited the unsafe conditions in both buildings which led to the high loss of life. The Code was reorganized and renamed the Life Safety Code in 1966. Even with the codes existence, and attempts by the NFPA and other life safety professionals to affect public policy and concern, subsequent fires continued such as the 1977 Beverly Hills Supper Club in which 164 people died and the 2003 Station Nightclub fire in Rhode Island in which 100 concert attendees perished. Every tragedy has led to changes in the code, but in each case, significant loss of life could have been avoided if the rules of the code had been followed. (2)

What about the Building Codes?

As in any free society, many people with the same positive intentions cannot always agree, or for various geographical or societal reasons cannot centralize their ideas. Such is the history of building codes in the United States. Three major organizations published building codes beginning in 1927 (earlier editions did exist for one of the three in 1905).

The three major codes were:

The Basic / National Building Code (BBC), first published in 1950 by the Building Officials and Code Administrators (BOCA); used primarily in the Midwest and Northeast United States

The Uniform Building Code (UBC), first published in 1927 by the International Conference of Building Officials; used primarily in the Western states, and

The Standard Building Code (SBC), first published in 1945 by the Southern Building Code Congress International (SBCCI).

In 1994, the three model code organizations created the International Code Council (ICC) to create a single set of model codes that would provide uniformity across not only the United States, but to help facilitate international use and promote innovation worldwide regarding new testing, research and products.

The ICC published its first set of model codes in 2000, consisting of the International Building Code (IBC), Fire Code (IFC), Mechanical Code (IMC), Plumbing Code (IPC), and others. These model codes have since replaced the BBC, UBC and SBC nationally, and are even used outside of the US. (3)

So what is the difference between the Life Safety Codes and Building Codes?

Building codes strictly control the allowable size, number of stories, height and structural systems used in any new building. They deal with gravity, wind, earthquake, snow and rain loads. The building codes deal with materials and systems with regards to structural integrity, water intrusion, durability, energy efficiency, accessibility and myriad of other topics. They also include many of the same requirements as the Life Safety Code with regards to fire protection, egress systems, fire sprinkler and alarm systems, etc.

Life Safety Codes such as NFPA 101 do not dictate building size, structural requirements, overall building area, or initial permitting. The Life Safety Code is concerned with one thing; the safety of life. I know it sounds repetitive, but the Life Safety Code is concerned with protecting the occupants during a fire while they stay put, or protecting them long enough to evacuate from a building or structure. While the building codes also prioritize the safety of the occupants, the Life Safety Code focuses solely on that idea.

So why can’t we just use the building codes?

This is a subject of great contention amongst those who design and construct any building that may have more than one AHJ. I believe it comes down to jurisdictions not stepping on each other’s toes. I will use healthcare in the United States as the example, because it’s easier to explain and is the focus of my own career. Every nursing home in the United States that wishes to receive federal funds under the Social Securities Act (whose programs include Medicaid and Medicare), must meet the federal requirements administered by the Centers for Medicaid and Medicare Services (CMS). They must also be licensed by the state in which they are built. CMS is a federal agency, and therefore its rules must cover every situation that may arise in every state, county and city. While some people would not want a federal agency telling them how to build or maintain their facility, you can guarantee that if a fire occurred in a nursing home which received federal funding, someone is going to look at the government for answers as to why it wasn’t safer.

So, why not let the local AHJ handle that safety issue on their own? The simple answer is that it’s not always possible. There are millions of Americans who live in areas of the country that have no adopted building code or even a local government capable of adopting or enforcing one. Texas is a prime example, in that areas outside of a city’s jurisdiction are not required to have a building permit and county governments are only allowed (not required) to adopt fire codes and not building codes. Trust me, I was as shocked to learn that one as many of my readers will be.

Remember, that a code is just words on paper unless a governmental agency adopts and enforces it. If no local enforcement agency exists, then CMS in this case MUST have a set of standards to meet. You can imagine the disaster if CMS only enforced safety standards for some areas of the country and not others. CMS is also kept from enforcing a building code as, there again; imagine the issues with a federal agency issuing and granting permits, and inspecting all construction in the United States on every single project it funds (even indirectly). I don’t care what your political affiliation may be; that’s just not a good idea.

Keeping the building codes and Life Safety Code separate allows for various AHJ’s to protect their citizens, without overstepping their bounds (too much).

So where do you get started?

Sounds like a good idea for my next post; a basic primer on the IBC and Life Safety Code. If there are other general topics regarding codes you have questions on, please leave a comment.

References / Footnotes:

(1) City of Dallas, Texas, Building Inspection, Construction Codes


(2) History of NFPA, NFPA.org


(3) Building Codes, IMUA, 1998



All NFPA Standards, Cover Images and references are copyrighted by the National Fire Protection Association®, One Battery Park, Quincy, Massachusetts 02169-7471. All references and images reproduced above are for educational and reference purposes only.

The International Building Code® and all other similar codes referenced above are copyrighted works by the International Code Council, Inc., 4051 West Flossmoor Road, Country Club Hills, IL 60478. All references and images reproduced above are for educational and reference purposes only

Beware the ‘rule of thumb’

As the building and fire safety codes are based entirely on exact measurements, testing procedures and other such criteria, making any code related decision based on a hunch, or estimation would be rather unwise.

Image from http://s.hswstatic.com

All too often on the jobsite, I’ve heard the phrase, “Well, I was always told the rule of thumb is….”. You can fill in the blank as to what code requirement someone has distilled into an easy to understand and 9 times out of 10, incorrect assumption. So, what is a “rule of thumb”, and why should you be wary of following any simple “rule” as far as codes go? First let’s start with the concept, and then follow with some extremely common and incorrect rules of thumb”.

So what does the phrase “rule of thumb” mean?

Gary Martin, Author and Founder of www.phrases.org.uk provides the following meaning and history of the phrase:

Rule of Thumb: A means of estimation made according to a rough and ready practical rule, not based on science or exact measurement.


The phrase itself has been in circulation since the 1600s. The earliest known use of it in print appears in a sermon given by the English puritan James Durham and printed in Heaven Upon Earth, 1685, “many profest Christians are like to foolish builders, who build by guess, and by rule of thumb, (as we use to speak) and not by Square and Rule.”

The origin of the phrase remains unknown. It is likely that it refers to one of the numerous ways that thumbs have been used to estimate things – judging the alignment or distance of an object by holding the thumb in one’s eye-line, the temperature of brews of beer, measurement of an inch from the joint to the nail to the tip, or across the thumb, etc. The phrase joins the whole nine yards as one that probably derives from some form of measurement but which is unlikely ever to be definitively pinned down.

I like Martin’s definition, specifically the phrase, “not based on science or exact measurement”. As the building and fire safety codes are based entirely on exact measurements, testing procedures and other such criteria, making any code related decision based on a hunch, or estimation would be rather unwise. While it’s understandable that anyone in the construction (or design) fields may want to simplify the rationale for doing something to direct their teams, workers, or supervisors quickly, this often results in a very watered-down version of a specific code requirement. Given enough time, the “rule of thumb” passes through so many people that it doesn’t even resemble the original statement. If you have never played the “telephone” game in grade school, I encourage you to Google it.


Rule of Thumb No. 1, “Electrical boxes that are in different stud cavities do not need putty pads”.

This rule deals with the requirements for metallic or non-metallic (plastic) electrical boxes that are installed in a fire-resistive wall assembly. The mere mention of a “stud cavity” exists nowhere in the commonly used building codes or standards that exist in the United States today. The International Building Code (IBC) and NFPA 101, the Life Safety Code (LSC), both require protection of any penetrations in a rated assembly to prevent its failure. Electrical boxes are specifically required by NFPA 70, the National Electrical Code to be installed in accordance with their listing. So here is what that listing says (taken from UL’s Guide QCIT.GuideInfo, Metallic Outlet Boxes, on www.ul.com):

Listed single- and double-gang metallic outlet and switch boxes with metallic or nonmetallic cover plates may be used in bearing and nonbearing wood stud and steel stud walls with ratings not exceeding 2 hr. These walls have gypsum wallboard facings similar to those shown in Design Nos. U301, U411 and U425, as covered under Fire Resistance Ratings – ANSI/UL 263 (BXUV). The boxes are intended to be fastened to the studs with the openings in the wallboard facing cut so that the clearance between the boxes and the wallboard does not exceed 1/8 in. The boxes are intended to be installed so that the surface area of individual boxes does not exceed 16 sq in, and the aggregate surface area of the boxes does not exceed 100 sq in per 100 sq ft of wall surface.

Boxes located on opposite sides of walls or partitions are intended to be separated by a minimum horizontal distance of 24 in. This minimum separation distance between the boxes may be reduced when Wall Opening Protective Materials (QCSN) are installed according to the requirements of their Classification.

The boxes are not intended to be installed on opposite sides of walls or partitions of staggered stud construction unless Wall Opening Protective Materials (QCSN) are installed with the boxes in accordance with Classification requirements for the protective materials.

You’ll notice very quickly that the words “stud cavity” do not appear in UL’s listing for Metallic Outlet Boxes, and to my knowledge do not appear in any other code, standard or listing. The 24” horizontal separation for boxes on opposite sides would definitely correlate to a wall built with studs at 24” centers, but it’s only a coincidence. In this case, the “rule of thumb” is 100% incorrect.

Rule of Thumb No. 2, “No storage is permitted anywhere within 18” of the ceiling in a building protected by sprinklers”.

This rule is simply a misunderstanding of the code requirements surrounding possible obstruction to the flow of water from a sprinkler head when activated. In this particular case, keeping all storage at least 18” away from the ceiling would definitely help in avoiding sprinkler obstructions, but when the same rule of thumb is used in reverse (to cite violations of the code), it would be very wrong.

NFPA 13, the Standard for the Installation of Sprinkler Systems, 2010 edition, states the following for standard upright and suspended (pendant) sprinkler heads:

NFPA 13, § Obstructions to Sprinkler Discharge Pattern Development Continuous or noncontinuous obstructions less than or equal to 18 in. (457 mm) below the sprinkler deflector that prevent the pattern from fully developing shall comply with

The following figures and charts from NFPA 13 show the required distances from any obstruction to the sprinkler head.

You’ll notice that obstructions less than 24” in depth are permitted when up against the wall of a room protected by a sprinkler (as depicted). This means that storage is permitted within 18” of the ceiling, but only in accordance with this section. Is it safer to just keep everything 18” below the ceiling? Yeah, it probably is, but spreading that requirement as a “rule” that uninformed people use as a “requirement”, only leads to confusion and conflict later (especially when used as a justification by inspectors).

What to do when everything you were told is wrong:

So I may have burst your bubble on two rules of thumb that are really not correct; what other rules of thumb are out there that could be wrong? I’d love to know. With some research, patience and willingness to challenge your past experience, we could eliminate those estimations and guesses; replacing them with the (sometimes simple) truth.

If you have some examples to share, or would love me to weigh in on, please write them in a comment. The more we discuss about what is actually correct or required the better off we all are.

Sources and Copyrights:

Excerpts from UL Guide QCIT.GuideInfo are reprinted from the Online Certifications Directory with permission from UL, © 2017 UL LLC

NFPA 13 and NFPA 101 are copyrighted by the National Fire Protection Association, and reproduced here for reference and educational purposes only