Archive for the ‘Comic’ Category

Arc-Flash, Take 2

Thursday, January 17th, 2013

As we learned in our last comic, open electrical panels are dangerous. To protect workers from these dangers, warning labels are required to be included on panels. The “Personal Protective Equipment”, or PPE, required to keep the worker safe while working on the panel when it is energized is listed.

Having learned from his last encounter, the ninja wisely takes a moment to put on the appropriate PPE. Bad luck follows the ninja, and he is struck again with an arc-flash. He is lucky that he is wearing his protective clothing. Unfortunately, “lucky” has a very strange meaning in the world of electrical safety. The recommended PPE limits the injuries to second degree burns on the face and body. Any part of the body closer to the panel than face and body, such as the hands and arms, needs a higher level of PPE to prevent third degree burns. The ninja will live, but he still has a long road to recovery.

The best practice, and the way to prevent these burns completely, is to work on the equipment while it is de-energized.

Arc-Flash, Take 1

Thursday, October 25th, 2012

An open electrical panel is a deceptively dangerous thing. The bus bars in the panel just sit there, doing nothing, giving no hint of their awesome power to instantly kill. If something causes a fault (or a short circuit to non-electrical engineers) between two bus bars, an incredible amount of energy is released. In fact, up close it rivals the power of a nuclear blast! What happened to the ninja occured in less time than his brain could even process it. In this case, he truly never knew what hit him.

Here are some videos of real arc-flash incidents to give you a sense of the danger.

Arc-flash demonstration. Watch the whole thing.

Arc-flash accident. Fast foward to 1:10.

Arc-flash accident. Fast forward to 1:10.

Mark Robison, PE

PS–curious about what the ninja discovered before his untimely death?

Current transformers are installed by utilities on large electrical services to avoid having gigantic electric meters. The current transformer converts the main building current to a lower value (between 0 and 5 amps) so that a standard meter can read the power. If the current transformers are bypassed, the current does not reach the meter and the electric bill is lower. Utilities have seal-locks on the meter section of the switchgear to alert them if cheaters have gained access.

In this case, the implication is that the current transformers are bypassed not to save money, but to give the appearance of using less power (and therefore appearing to be a more green building than it really is).

Motel 6

Wednesday, October 10th, 2012

If you are old enough to recall the voice of Tom Bodett saying, “We’ll leave the light on for you” as the signature end to all the Motel 6 ads, then you caught the attempt at humor. But even if the reference passed over your head, the message remains the same.

As a true believer in the Green movement, I applaud the work being done to reduce energy consumption, including lighting energy savings. But as with all regulations intended for the greater good, unintended consequences can occur for specific situations.

One area where I see too many restrictions is in regard to commercial lighting where the lighting is really part of the product, and not just an arbitrary element. To the credit of the USGBC and other regulatory agencies such as T-24 in California, the code is including more subtlety to allow commercial establishments to maximize their business plan.

Meanwhile, our MEP Ninja has gotten caught in the cross fire, and is having a bad day, as he always seem to have.

Mark D. Robison, PE

California Electric Reheat

Sunday, July 1st, 2012

“Reheat” is the term used by air conditioning engineers to describe the process of reheating supply air of a variable volume air conditioning system. In a variable volume system, all rooms get the same cool air from a main air handler.

If one or more of those rooms gets too cold, the air is locally heated to make the space comfortable. This reheat can be done with either electric heating coils or with hot water heating coils. Electric coils are less expensive to install but use electricity rather than gas (used to heat the hot water) as a fuel source.

In California, the use of electricity is strongly discouraged by the Title 24 energy code. Thus, electric reheat is prohibited in California.

There is an exception, however. When the Title 24 calculations are done in conjunction with other factors such as boiler piping loss, electric heat may meet the energy code. It would appear that the USGBC did a full energy model proving electric heat to be an efficient energy choice. And MEP Ninja was “shocked” to make this discovery.

Mark D. Robison, PE

Variable Refrigerant Flow Systems

Wednesday, February 29th, 2012

Variable Refrigerant Flow (VRF) systems or Variable Refrigerant Volume (VRV) systems are a new kind of air conditioning in the US. They were originally developed in Japan in the early 80’s, but have only recently started to be used here. The systems take advantage of high tech controls to allow more than one hotel room to be connected to a single condenser mounted on the roof. The VRF units are very efficient and quiet, making them the most comfortable hotel room temperature control you could ever imagine.

But there is one catch. Multiple hotel rooms are connected to a single condenser and they share a common piping system for the refrigerant. If a leak occurs in a single unit, all the refrigerant in the system goes into one room. The resulting concentration of refrigerant can be lethal.

This danger has prompted many hotel chains, including Marriott and Hilton, to ban these systems from use in their hotels. There is an exception to this rule if costly refrigerant leak detection alarms are added to the rooms.

In this comic, the refrigerant began filling the room when the VRF unit was struck with the throwing star. The leak detection alarm might have saved the ninjas had it not been cut in half. Unfortunately, there is no NEMA rating that corresponds to “provides protection against ninja sword fights.”

Mark Robison, PE

Vertical Wires

Wednesday, February 15th, 2012

The issue shown in this comic is a real concern in the electrical industry. The wires in a tall building are incredibly heavy. If they fall through an open conduit, they can trap and crush anyone in the electrical room. Only after they are terminated in a switchboard is it safe to be in the room.

In a finished building, the conductors are supported every few floors to protect against this possibility and to reduce the strain on the wires. During construction, if the wire is pulled in a single run from the bottom of the building, there is significant danger if the pulling rope fails.

There are two ways of reducing this danger during construction. The preferred method is to pull the wire from the roof down to the lower levels. Of course, care must be taken to make sure that the wire never gets loose at the roof. The alternative method is to pull the wire from the bottom a few floors at a time to a junction box, lay the extra wire out on the floor, then secure it in the conduit. The extra wire is then fed back into the conduit for several more floors and the process is repeated.

What happens to the ninja in this comic really should not have occurred. The supports should have held the wires in place and prevented them from falling into the room. The ninjas would have been foiled, but not dead.

Mark Robison, PE

BIM vs As-Builts

Wednesday, February 1st, 2012

Oh, how naive our ninja is! He thought that the plans for the building would match what was actually built. Silly ninja.

There is a term in the construction industry called “as-builts”. These are drawings that have been updated to match what actually got built. Hence, “as-built”.

With the advent of BIM (building information modeling) and 3D modeling, the theory is that the model is so realistic that there will be no need for “as-building” the plans. The model and the building will be exactly the same.

But real life is still messy, and changes during construction happen all the time. Sometimes there is an error in the design that needs to be fixed. Sometimes designers and contractors come up with ways to improve a design. All of these reasons to change a design apply to both traditional plans and BIM. Using BIM does not prevent these changes, though it hopefully reduces the number and allows them to more easily be made.

As-building the plans is a necessary step at the end of the project in order for the final plans and the building to match. This extra step costs extra money that owners are seldom willing to pay. As-building is a very tempting process to skip to save money after construction. Using BIM might make creating the as-built model easier, but it still takes time and money.

In the comic, like in most buildings, as-building the model did not happen. The ductwork in the stolen BIM file and the ductwork in the building don’t match, and the ninja ends up dumped into an alley rather than his foe’s office.

Or maybe what really happened is that the Green LEEDer planted false plans to foil the ninja. Oh, how clever those USBGC folks are.

Mark Robison, PE

Hoodie Draw Strings

Wednesday, January 18th, 2012

Do you remember the Honda Civic ad with the cute ninja girl and “Hoodie Ninja” playing in the background? I was so inspired by that ad that I went out and bought . . . no, not a new car . . . but a hooded sweatshirt! And I wear it all the time.

I do a lot of construction, and have come to realize that the drawstrings of a hoodie pose a significant safety hazard around rotating machinery. In days gone by, the fashion of wearing ties was a danger to engineers in the field. Now I no longer wear a tie and I have removed the drawstrings from my hooded sweatshirts.

Hoodie ninja learns that lesson the hard way here. Little did she know that climbing the side of the USGBC building would be the safest thing she did that night.

And pity poor MEP ninja! Just when he found the ninja of his dreams who shared his passion for MEP systems, he losses her on their first date. But it might not have worked out anyway, since he would later learn that she was LEED accredited.

Mark Robison, PE

Cell Tower

Wednesday, December 28th, 2011

While walking around on roofs doing field work, I have encountered lots of cell towers. The towers always have warning signs posted on them, telling you to not walk in front of them because of the huge amounts of energy at the face of the antenna. The radiation to the side and behind the antenna is significantly less than what comes out the front. When walking around on the roof, you must be careful to not get cooked.

In this comic, our ninjas are using the cell tower energy to roast their marshmallows. Their marshmallows will end up microwaved, and not toasted, but that’s the best they can do on a roof without starting a fire.

Merry Christmas from MEP Ninja!

Mark Robison, PE

Fan Pressure

Wednesday, December 14th, 2011

The air pressure in the various parts of an air handler are different–a lesson that the ninja experiences first-hand in this comic! On the air intake side, the air pressure is negative because the fan is sucking. On the other side of the fan, the air pressure is positive and blowing outward.

So why can’t the strong ninja handle the forces on these doors? Let’s do a little math.

A typical air pressure on a fan is about 4 inches of water. To understand what this means, think of a drinking straw. When you suck on the straw and the drink rises 4 inches up into the straw from the top of the drink, you are demonstrating 4 inches of static pressure. No big deal, right? Well, let’s figure out what the force on the door is.

First, let’s convert inches of water pressure to pounds per square inch. If your straw was 28 inches long, and you sucked all the way to the top, that would be 1 pound per square inch of pressure. Divide 4 by 28 to calculate a pressure of 0.14 pounds per square inch on the door.

If the door is 2 feet by 6 feet, that is 12 square feet, or 1,728 square inches.

Multiply 0.14 pounds per square inch by 1,728 square inches and you get 242 pounds of force on the door. Not all of that is directed at the ninja–some of it goes toward the hinge on the door. The actual force at the handle would be about 120 pounds . . . or enough to knock you over if you are not prepared!

Mark Robison, PE