Origin of Plenum cabling rules? 1980 MGM Grand fire or 1970s TelCo fire?

[PetesGuide]

While installing some Ethernet cable in plenum spaces at a Red Cross facility, I've been fighting some battles with technology volunteers who think they can ignore the Code, and that doing so is safe.

One of the discussions pointed me to a Wikipedia article that they thought indicated plenum-rated wiring itself has only existed since the 1990s (!!!!!), and that led me to track down the origin of the plenum wiring requirement. I kept finding references to the "1975 MGM Grand fire", which led to the plenum requirements in NEC-1978.

But when I researched the 1975 fire, I discovered it was in fact a 1980 fire, and thus couldn't have caused the plenum requirements in NEC-1978.

That led me to this article: http://www.sdmmag.com/articles/84601-what-technicians-need-to-know-about-cable-the-nec

Does anyone here have the historical references that will shed light on this?

 

[mgookin]

While installing some Ethernet cable in plenum spaces at a Red Cross facility, I've been fighting some battles with technology volunteers who think they can ignore the Code, and that doing so is safe.

One of the discussions pointed me to a Wikipedia article that they thought indicated plenum-rated wiring itself has only existed since the 1990s (!!!!!), and that led me to track down the origin of the plenum wiring requirement. I kept finding references to the "1975 MGM Grand fire", which led to the plenum requirements in NEC-1978.

But when I researched the 1975 fire, I discovered it was in fact a 1980 fire, and thus couldn't have caused the plenum requirements in NEC-1978.

That led me to this article: http://www.sdmmag.com/articles/84601-what-technicians-need-to-know-about-cable-the-nec

Does anyone here have the historical references that will shed light on this?

There are two different things to consider:
1. Plenum rated cable has nothing to do with fire spreading from one floor to another. It has everything to do with products of combustion in a supply or return air stream. You don't want burning cables to produce products of combustion and have the products of combustion pumped into a means of egress. Make sure you thoroughly understand what a plenum is and this makes sense. You can have a plenum in a single story building.
2. We studied the MGM Grand fire and many other high rise fires in Florida Fire College as well as at the National Fire Academy. The MGM lacked adequate draftstopping and fireblocking. The fire got to the ceiling of the main floor and quickly spread across that ceiling and up through unprotected vertical openings in the structure allowing the fire to quickly spread to upper floors of the building. Having plenum rated cable would have done nothing to prevent the tragedy.

 

[cowboyjwc]

There are two different things to consider:
1. Plenum rated cable has nothing to do with fire spreading from one floor to another. It has everything to do with products of combustion in a supply or return air stream. You don't want burning cables to produce products of combustion and have the products of combustion pumped into a means of egress. Make sure you thoroughly understand what a plenum is and this makes sense. You can have a plenum in a single story building.
2. We studied the MGM Grand fire and many other high rise fires in Florida Fire College as well as at the National Fire Academy. The MGM lacked adequate draftstopping and fireblocking. The fire got to the ceiling of the main floor and quickly spread across that ceiling and up through unprotected vertical openings in the structure allowing the fire to quickly spread to upper floors of the building. Having plenum rated cable would have done nothing to prevent the tragedy.

That is correct, and while the cabling was not a factor, it's still illustrates the importance of fire stopping. I tell contractors, who don't seem to have a grasp on fire stopping, to read the MGM report and it will give you a new outlook on it. Also part of the problem with the LV industry is that many cities, ours included, don't require permits for low voltage. So while inspecting new work we can keep them in line, it's when they come in after the fact that you will see many of the violations.

 

[GoldDigger]

There are two different things to consider:
1. Plenum rated cable has nothing to do with fire spreading from one floor to another.

Riser cable, on the other hand, is specifically tested for vertical flame spread.

Also, is the space the OP is working in actually an environmental air space? Not all dropped ceiling installations are configured to act as HVAC air returns.

 

[EV607797]

The 1975 fire in NY Telephone's central office was spread throughout the building largely due to riser cables. At the time that many of these cables were installed, cables weren't evaluated the way that they are today. In fact, if anything, this fire brought on the development of riser-rated cables for use in vertical installations everywhere, not just in telco central offices. Many of the cables in this building were very old as well, installed decades earlier. Lead-sheathed underground cables with paper-insulated conductors entered the cable vaults below grade. They were then spliced to lead-sheathed cables with cotton-insulated conductors for routing to the termination frames, often many floors above. These cables being jacketed with soft lead melted in the fire rather quickly and exposed the cotton insulated cable pairs. That had a big part in the fire spread from the cable vault to floors above.

As stated earlier, the 1980 fire at the MGM had more to do with faulty floor penetrations.

 

[zbang]

For fun, I'll offer two more-
Probably the most common high-quality coax for analog video was Belden 8281. Great stuff but polyethylene (basically jellied kerosene) insulation so it burns like a candle. A friend was fairly instrumental in getting ABC NY to stop using the stuff for new installation there and to remove the existing when they could. How about some raised floors full of the stuff?

Much worse was the Spectator Mine fire (Butte, MT, 1917)- oiled insulation and carbide lamps do not mix and both in a multi-thousand foot deep shaft was a recipe for disaster.

 

[norcal]

That is correct, and while the cabling was not a factor, it's still illustrates the importance of fire stopping. I tell contractors, who don't seem to have a grasp on fire stopping, to read the MGM report and it will give you a new outlook on it. Also part of the problem with the LV industry is that many cities, ours included, don't require permits for low voltage. So while inspecting new work we can keep them in line, it's when they come in after the fact that you will see many of the violations.

LV installers irk me, have had some issues with them damaging firewalls, to run their cables & then leaving the carnage to be found by others, for that reason & others my opinion of them is that their only value in life, is for them to be used as the subjects of medical experiments.

 

[don_resqcapt19]

....
1. Plenum rated cable has nothing to do with fire spreading from one floor to another.. ....

It actually does as plenum cable is required to meet all of the requirements of riser cable and also be low smoke producing.

 

[PetesGuide]

Thanks everyone!

All of your comments have helped me get a starting point on my research.

Some of the interesting things I've learned so far include:

• There was another 1975 fire at the now-gone World Trade Center that appears to be more applicable to the plenum cable regulations.
• The 1975 change to the NEC or NFPA 90A actually appears to have been a loosening of regulations (previously, all low-voltage cabling in a plenum had to be enclosed in metal conduit or similar).
• The original low-voltage plenum rules appear to date to 1936.