Fire at Michigan State Champs

[vhcook]

My assumption is that the early poking around near the fire was an attempt to find and hit the main breaker, which is usually the first line of defense before they go to the extinguishers. Even when clearly labelled, the smoke can make it really hard to see the breaker. Blowing on the flames, however, was probably not the best plan.

Later, they popped the cover to make it easier to get the fire extinguisher onto the fire.

[Jaci]

Originally Posted by orangemoore

What are your concerns with a battery and fire?

It's moreso that a battery rupture could cause massive damage to the internals of the robot and any close components assuming the bellypan of the robot isn't fully enclosed.

It was stated that the fire was caused by a battery short with a live chassis. If a robot is on fire, 9 times out of 10 it will be because of a battery short or electrical fault. When a high amperage electrical circuit shorts, touching the metal chassis of the robot is a good way to become less alive.

[Doug Frisk]

Originally Posted by Jaci

I hate to be 'that person', but it has to be said.

Why did it take so long to grab a fire extinguisher that should have been ready at the field?

Because someone screwed up. As part of field setup, the fire extinguisher is removed from case 8 and put by the side of the field. I usually put it in front of the FMS at the center of the table or on the end of the table where the FTAs are hanging out.

It's quite apparent that extinguisher was still in case 8. I bet all the FTAs get an email this week.

[Jaci]

Originally Posted by vhcook

My assumption is that the early poking around near the fire was an attempt to find and hit the main breaker, which is usually the first line of defense before they go to the extinguishers. Even when clearly labelled, the smoke can make it really hard to see the breaker. Blowing on the flames, however, was probably not the best plan.

Later, they popped the cover to make it easier to get the fire extinguisher onto the fire.

At this point, hitting the breaker won't solve the problem. The fire is started electrically, which means that something, somewhere has shorted. Not only does this trip the breaker/fuse, but will also discharge the battery if the breaker isn't fast enough to catch it.

[Jaci]

Originally Posted by DareDad

Because someone screwed up. As part of field setup, the fire extinguisher is removed from case 8 and put by the side of the field. I usually put it in front of the FMS at the center of the table or on the end of the table where the FTAs are hanging out.

It's quite apparent that extinguisher was still in case 8. I bet all the FTAs get an email this week.

I'm aware that fire extinguishers are standard with the field, but the fact that it was neglected/forgotten by the field setup crew is what worries me.

[Doug Frisk]

Originally Posted by Sperkowsky

It seems to me that they were searching for a dry chemical fire extinguisher apposed to a more common co2 fire extinguisher in order to keep parts of the robot salvageable.

The likelihood hood of the fire spreading was very low but, it did slightly concern me when they started to poke around inside of the robot. I was also expecting with that size flame that the bumper fabric would eventually catch on fire. Overall it just seemed foolish to poke around.

The reaction time could have definitely been better and this is a situation that volunteers should be better prepared for but the likelihood is pretty low.

A more accessible fire extinguisher is really all they need.

You have that backwards. A dry chemical extinguisher will coat the robot in dust and crap, CO2 leaves no residue making it easier to salvage bits.

I'd also call dry chemical much more common. C02 extinguishers are not typically found at your big box home store.

I've never actually seen a CO2 unit in a pit at an FRC event. I'm sure some teams have them, but dry chemical is pretty much what everyone has.

[Kevin Sevcik]

Originally Posted by Jaci

When a high amperage electrical circuit shorts, touching the metal chassis of the robot is a good way to become less alive.

You might be badly burned if the frame is hot, but Ohm's law plus physiology says you're extremely unlikely to suffer any injury from the electricity itself. Wikipedia says the resistance of wet skin is about 1 kOhms. So a 12V battery can push, say, 12 mA through you. The chart on that page notes that 12 mA of AC would be noticeable after a few seconds, but not deadly. It's important to note that DC is much less dangerous in this regard than AC. Unless you have wires connected directly to your heart[1], it takes a lot more DC to kill you than AC. If anyone is doubtful, I can hold a demonstration at Champs where I will bravely grab both terminals of a robot battery with either hand an suffer no ill effects.

Mind you there's plenty of other dangers from the battery, but they're all the fire, explosion, direct-short causing a welding arc sort.

TL;DR: The robot battery (and your car battery[2]) aren't going to electrocute you unless you stab a positive and negative wire from them into your heart. In which case you have plenty of other problems besides.

[1]I have before. It was weird.
[2]Had a dead battery once in college and got a jump from a doctor. He gave me the same electrocution warning. And he should know, because he's a doctor. I didn't argue because I wanted to get home.

[rsisk]

If there was a short with the frame, does this mean the frame isolation test during inspection was not done?

Or would this happen even if the frame isolation test passed?

[Jaci]

Originally Posted by Kevin Sevcik

You might be badly burned if the frame is hot, but Ohm's law plus physiology says you're extremely unlikely to suffer any injury from the electricity itself. Wikipedia says the resistance of wet skin is about 1 kOhms. So a 12V battery can push, say, 12 mA through you. The chart on that page notes that 12 mA of AC would be noticeable after a few seconds, but not deadly. It's important to note that DC is much less dangerous in this regard than AC. Unless you have wires connected directly to your heart[1], it takes a lot more DC to kill you than AC. If anyone is doubtful, I can hold a demonstration at Champs where I will bravely grab both terminals of a robot battery with either hand an suffer no ill effects.

Mind you there's plenty of other dangers from the battery, but they're all the fire, explosion, direct-short causing a welding arc sort.

TL;DR: The robot battery (and your car battery[2]) aren't going to electrocute you unless you stab a positive and negative wire from them into your heart. In which case you have plenty of other problems besides.

[1]I have before. It was weird.
[2]Had a dead battery once in college and got a jump from a doctor. He gave me the same electrocution warning. And he should know, because he's a doctor. I didn't argue because I wanted to get home.

That is a fair point, I should have thought a bit further before posting that last line. Looking back, I should have known a bit better[1]. Even so, I still stand that touching an electrically charged chassis is far from a good idea, even if it's just for peace-of-mind.

[1]I do a lot of work with electrical systems. Also got shocked by a 240 ~3-6A wall socket (for the second time) a few years ago, less than a fun experience.

[Jaci]

Originally Posted by rsisk

If there was a short with the frame, does this mean the frame isolation test during inspection was not done?

Or would this happen even if the frame isolation test passed?

It is possible even if circuits are electrically isolated from the frame before the match. If the outer shielding of the wire (or a solder joint, or wire crimp) becomes damaged, it is very possible for it to contact the robot chassis. With the rigors of Stronghold, this is entirely within the realm of possibility.

[Karibou]

Originally Posted by DareDad

Because someone screwed up. As part of field setup, the fire extinguisher is removed from case 8 and put by the side of the field. I usually put it in front of the FMS at the center of the table or on the end of the table where the FTAs are hanging out.

It's quite apparent that extinguisher was still in case 8. I bet all the FTAs get an email this week.

Unless it changed this season, Michigan does not use the standard road case system that the rest of the country uses. There is no case 8, just a toolbox and a tote or two with the non-tool items that are usually in case 8 (paper towel glass cleaner, etc). I'm actually not sure where the fire extinguisher is stored with Michigan fields.

Disclaimer: I didn't do any events in Michigan this year, so it may have changed.

Originally Posted by rsisk

If there was a short with the frame, does this mean the frame isolation test during inspection was not done?

Or would this happen even if the frame isolation test passed?

Or maybe it happened after inspection? Wire coming loose during a match?

[Doug Frisk]

Originally Posted by Karibou

Unless it changed this season, Michigan does not use the standard road case system that the rest of the country uses. There is no case 8, just a toolbox and a tote or two with the non-tool items that are usually in case 8 (paper towel glass cleaner, etc). I'm actually not sure where the fire extinguisher is stored with Michigan fields.

You make a good point. Though the extinguisher that came out eventually did look like the standard CO2 extinguisher packed with the regional fields.

[Jon Stratis]

Originally Posted by rsisk

If there was a short with the frame, does this mean the frame isolation test during inspection was not done?

Or would this happen even if the frame isolation test passed?

There's a lot of variables that can go into this, we can't say for certain if it was or was not done. It's possible it was done, but after the fact the insulation wore through. It's possible the frame short was intermittent, and only occurred when a wire was pinched in a mechanism a specific way. Or the team was doing a hasty repair and pinched a wire, or drilled through the insulation of a wire, or disconnected a motor and had the leads just dangling... There are any number of ways for the frame to short out either before or after a frame isolation test is done. And most of the time the frame isolation test is not performed during reinspection.

The reason we do the frame isolation test is to ensure that it takes two faults to cause a problem, not just one. Two faults obviously can still happen, but it's half as likely to happen as having one fault.

[Calvin Hartley]

Originally Posted by Karibou

Unless it changed this season, Michigan does not use the standard road case system that the rest of the country uses...

This is correct. (Though I am far from an authority on the topic, I've helped with a handful of event setup and teardowns.)

[FrankJ]

Originally Posted by Jaci

Even so, I still stand that touching an electrically charged chassis is far from a good idea, even if it's just for peace-of-mind...

You are aware your car has an electrically charged chassis? In the States we bond one leg of of our power to ground. Touching a charged chassis really isn't an issue. You don't want to use your body to complete the electrical circuit though.

Before using your extingisher on an electrical fire, you want to remove the inigtion source. Powdered fire extinguisher are messy. Never my first choice when other options are present.