Stage Collapse and the Emergency Shutoff: Remember the Liberté

Even before forensic engineers report back (Thornton Tomasetti of NYC is one) on the Indiana State Fair stage collapse, are there any lessons?

One item that caught my attention was on the TheatreSafety blog.

TheatreSafety points out that according to this chronology of events, 22 minutes passed between the collapse and when somebody shut off the electrical feed to the wreckage.

That time delay posed a substantial risk to the rescue that got underway immediately. Much of the collapsed structure was of conductive metal, intertwined with power cables, electrical hoists, spotlights, and video equipment that had been suspended from the fly system.

From Vincent Dunn's website on fireground safety, here's an expert view about why quick access to utility shutoffs is so important at emergency scenes:

“Explosions and structural collapse rip open walls, ceilings and floors of a structure. Live electric wires are threaded throughout the rubble, hanging dangerously in midair and laying around the ground. A collapse search and rescue plan must be put into action. This plan must include: safety survey and reconnaissance, surface search and rescue, void search, selected debris removal and general rubble removal. One of the most important parts of the first step of the collapse rescue plan is to shut off all the utilities such as water and electricity. Shutting off electric power can save the lives of searching firefighters and trapped victims in the collapse rubble."

Since some jurisdictions allow temporary outdoor stages to operate in a complete regulatory vacuum, it's likely there will be more collapses that trap entertainers, workers, and members of the audience. So somebody has to plan ahead on turning the power off.

The location of the circuit breaker must be well-marked and outside of the probable collapse radius. It's no help if the breaker panel is at the base of the debris field and can't be reached without someone being electrocuted on the way in.

How to pass along the information about the breaker panel? Signage is one way, but signs can be overlooked in the confusion of a disaster. Officials at some public buildings have combined a vital set of items in a single container at each site called the Crisis Response Box. The CRB is a set of building plans, keys, phone numbers, and other time-critical information assembled ahead of time that can save lives in an emergency. This CRB guidebook from California offers a relevant lessons-learned item from the 1999 attack at Columbine High School:

"During the incident at Columbine, no one was readily available who knew how to immediately turn off the sprinkler system. As a result, hallways quickly filled with water, making it difficult to escape.  In some places, the water reached dangerous levels in proximity to the electrical outlets – water reaching such outlets could have caused many more injuries and possibly additional deaths."

For an historical example of why emergency shutoffs have to be thoughtfully located, see this account in Inviting Disaster of an ammunition fire aboard the battleship Liberté in Toulon Harbor.

In that 1911 crisis, a forward magazine of ammunition loaded with the volatile Poudre B composition caught fire spontaneously. A two-man crew had scant minutes to get to the bow and open seawater valves that would flood the magazine before the magazine would explode, but they found it impossible to reach the valves because some thoughtless person had located the flooding controls directly above the powder magazines. During the crew's third frantic try to breach the smoke and flames and reach the valves, the ship blew up. 

Moral: as humans we're supposed to have the unique ability of anticipating the future and weighing actions we haven't taken yet. So apply that forebrain! 

Sunsets and Anti-Sunsets

When stopping to photograph a spectacular sunset or sunrise, look in the opposite direction too, at what might be thought of as the antipodal clouds. 

Antipodes are two spots on the Earth's surface that lie directly opposite; if one hammered a rod straight through the planet, it would hit both spots. For those who want to check out their own antipodal point, try out this nifty interactive map. (Using the hand cursor to slide the image, center the top map on your location. The lower map will show the antipodal point.)

The antipodal point of my neighborhood is a trackless patch of the Indian Ocean, midway between Australia and India but more southerly. Well, not quite trackless. I was surprised to see a big island that I've never heard of, a territory of France called Kerguelen. It's one of the French Southern Lands. The antipodal point of Kerguelen is south of Medicine Hat, Alberta, Canada. Here's a picture of Kerguelen's rock-ribbed headlands, what to me was terra incognita until just now:

Back to cloud-hunting. I concede that using the word "antipodes" is a stretch when it comes to cloud photography .... How about "anti-sunset"?

An anti-sunset photo would be one taken 180 degrees opposite of the sun's location on the compass: if the sun is hitting the horizon at 285 degrees on the compass, the anti-sunset happens at 105 degrees. Sometimes the anti-sunset is nothing special -- there are no clouds, or they lack features to catch the light -- but sometimes the anti-sunset outclasses the showier sunset. 

Here's an example of a recent, decent sunset in my area. Nothing outstanding, but I liked the warm, warbly texture.

Next, here's an anti-sunset photo the same evening.

Because the background sky of an anti-sunset is dark, sunlit clouds have a way of standing out. Here's a painting-like view of clouds off to the side:

A second photo halfway between sunset and anti-sunset. Notice how it has more depth than the showy sunset?

So, winding up: sunsets are fine and I love to watch them as much as anyone, but they tend to be short on subtlety and depth. So don't forget to take a spin and look at the whole sky!

Tales of Coffman: In Praise of Engine Starters

Difficulty with starting our lawnmower recently reminded me of the under-appreciated class of devices called engine starters. We take them for granted, never offering a word of praise over the years; then at the first sign of trouble we consign them to the nether regions. As consumers most of us have experience with only two kinds. One is the recoil starter for small engines, in which a pull on a cord provides inertia to the engine crankshaft and direct current to the spark plug. The other is the ubiquitous electric starter on our cars, in which a battery-powered motor turns the engine over.

But there's lots more variety, then and now. Early carmakers experimented with compressed-air starters and ones drawing acetylene gas from the supply for the headlights. 

RC aircraft enthusiasts sometimes use a cordless drill to start tiny gasoline engines. When I worked in construction with my brothers, we drove a variety of stick-shift gasoline-fueled trucks and appreciated the option that a standard transmission gave us to roll-start the trucks on a hill.

Starting a diesel engine needs extra power since the fuel must be compressed more than with a gasoline engine. On some old Caterpillar dozers, the operator used a recoil starter to get a small gasoline engine going, and then used that power to crank the diesel engine. Also handy: a can of starting ether, aimed at the air intake.

A common method for firing up large gasoline and diesel engines of yesteryear was the Coffman starter. Inserted into a sturdy breech, a blank shotgun cartridge sent a blast of pressurized gas down a steel tube. In some versions the hot gas spun a turbine that transferred its inertia to the engine for starting.

A powder start is smoky and loud, as in this video showing its use with a jet engine. Here's a rather lengthy but interesting video of how to start a "Field Marshal" diesel tractor with a Coffman starter. The breech is at the front of the tractor, rather than at the driver's seat. The process includes the use of what looks like a cigarette as a glow plug. (Glow plugs are particularly important when starting diesels at low temperatures, because the frigid engine block steals heat from the compressed vapor).

Pros: the Coffman starter was lighter and smaller than crank-driven inertial devices or the battery-and-electric-starter combination. It was well suited for starting big-engine aircraft and tanks in remote areas. 

Con: run out of powder cartridges, and you're out of luck.  

The Flight of the Phoenix (1965, remade in 2004) raised the profile of Coffman starters, because the characters' triumphal return to civilization can't start until the radial engine does. In the movie, a group of airmen and oilfield hands undertake to salvage something flyable from a wrecked twin-engine C-82A Packet in the Sahara Desert. 

After the improvised monoplane is hammered together Capt. Frank Towns (played by Jimmy Stewart) undertakes to crank over the gang's improvised single-engine monoplane with a Coffman starter, but has only seven cartridges to do so. The radial engine is so big there's no other way they'd be able to start it up. Defying the plane's designer, an irritating German, Towns uses one cartridge to clean out the cylinders, firing it with the magneto off. The engine eventually catches, of course, so our heroes can complete their self-rescue by flying to an oasis. 

I think the triumphal scene as the engine catches and warms up is a bit long, but when it comes to guy-movie moments, it hits the mark.

Deadly Chinook Crash in Afghanistan: RPG or not?

Sad news of a tandem-rotor CH-47 crashing as it was taking off at night with 31 American and seven Afghan troops on board. The crash followed a firefight in the Tangi Valley, Wardak Province. Most likely it was an aircraft operated by the Special Operations Aviation Regiment; my earlier post on SOAR is here.

News accounts say that a hit by a single rocket propelled grenade was probably the cause. The Eastern bloc RPG-7 has been a cheap, rugged, effective launcher for unguided projectiles. 

The most commonly pictured warhead is the PG-7VL conical model carrying a shaped charge, but warheads also come in thermobaric and fragmentation varieties. 

It's possible that the launch of a single RPG fragmentation round -- what some call the Golden BB -- was the cause but I'd be surprised. Early in the Russian invasion of Afghanistan, Afghan fighters tried aiming single RPGs at Russian helicopters but it hardly ever knocked a transport or gunship down, even under prime shooting conditions in the daytime. Aiming the unguided RPG accurately at night at a blacked-out, moving helicopter would be extremely difficult. It's even less likely that a single hit would be fatal. 

So my speculation is that either a guided MANPAD missile was involved, or else a multiple-RPG ambush. Multiple RPGs were involved in the "Black Hawk Down" incident in Mogadishu.

Some of the most effective anti-helicopter tactics developed by Northern Alliance fighters against Russian helicopters relied on an ambush by heavy machine guns or multiple RPG launchers. If RPGs were used these were at a half-mile distance, fired simultaneously to use the timed warhead as a flak round. An unclassified US training manual on the RPG-7 is here.