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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 17th Apr 2018, 10:39 am   #1
astral highway
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Default CPU cooling fan - blind-spots in risk/ personal safety assessment?

I think of myself as a risk-aware person, but I had a reminder yesterday that risk is greatest in areas we know least about, or around equipment we have the least specific experience with.

I'd built a small circuit requiring a heatsink and forced-air cooling. It was a lash-up and had a MOSFET as a power device, operating at high pulse power but a very low voltage.

I selected the largest of three cooling fans in my collection. This one, a .95A, 12V model with quite a large radius, plastic throughout. We've probably all seen many of the smaller cousins of this, but I was curious to try the larger one in a role where its power was needed.

I rested it on my work-surface and just to check the polarity, applied power to the fan, thinking the test would be just for a couple of seconds. I had prepared a clamp to hold it in place once I'd sussed this.

As soon as I switched it on, it slid back really quickly towards the alu heatsink and I instinctively grabbed what I thought was the top of the case, to prevent a collision.

My fingers must have curved over into the blades. Next thing, there were blobs of blood over my DC power supply and 'scope. I looked down and noticed I had two deep cuts in my fingers, L2 and L3. This fleeting contact broke one of the fan blades.

The cuts were parallel to the nail-bed but on the pads. As an experienced first-aider, I managed to do clean and patch them up pretty quickly by myself with steri-strips and plasters, but they are out of commission for now as the cuts are still sensitive to pressure.

It's not as bad as it probably sounds - I'll be fine by tomorrow. The fan is in the bin as the broken blade wrecked the balance.

I know Newton's third law, and I'd put the clamp on the desk to address this, but I overlooked the proximity of the fan and the heatsink for my polarity check.

I thought carefully about posting this as sometimes, the safety components of threads can go in a finger-wagging direction that can seem predictable and overwrought.

But in this case, I'm happy to share the near-miss experience. I'm doing so to invite others to share aspects of what we do on the forum that are inherently risky - but that we don't think so much about (so not shock hazard, for example - that's pretty much taken as read.)

The 'correct' action, easy in hindsight, was to power down, but I didn't recognise it at the time.

The experience has made it clear to me that it's unacceptably risky for me to operate the vintage Klystron cooling fan that I thought I'd get going. It's a 115V, 5700 RPM model with alu blades.

No, thank you.

So, over to you!
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Old 17th Apr 2018, 11:14 am   #2
ionburn
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Default Re: CPU cooling fan - blind-spots in risk/ personal safety assessment?

These things are done in an instant. I think the main one I worry about is having mains connections to a lash up. I make a deliberate move to separate these connections as it is easy to move without thinking. The worst similar accident I came across was a friend who knocked a scalpel off the front of the bench and closed his knees to catch it. Nothing too major but was a visit to A & E.
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Old 17th Apr 2018, 11:22 am   #3
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Default Re: CPU cooling fan - blind-spots in risk/ personal safety assessment?

The big fans can do a lot of damage. I save wire fan covers from scrap equipment and always try to fit them, but it's all too easy to get careless. Fortunately I've escaped without serious injury so far.
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Old 17th Apr 2018, 3:19 pm   #4
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Default Re: CPU cooling fan - blind-spots in risk/ personal safety assessment?

Enlarging the hole in a large brass solder tag, with a power drill.

Drill too sharp and tip angled for cutting steel, work piece not clamped, wire still attached to solder tag. You can guess what happened.

The hole in my fingernail took a long time to grow out since it was right at the base.. i had to renew the superglue repair a couple of times a day to stop the ripped nail catching on things.
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Old 17th Apr 2018, 3:42 pm   #5
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Default Re: CPU cooling fan - blind-spots in risk/ personal safety assessment?

I have found that if I drop something hot or sharp I have to work quite hard to get my conscious brain to quickly tell my unconscious brain to not try and catch it.
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Old 17th Apr 2018, 4:51 pm   #6
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Default Re: CPU cooling fan - blind-spots in risk/ personal safety assessment?

It's a reaction that can be learnt, though.
I now 'instinctively' step back if I drop something sharp.

I think that there's a difference between that sort of accident, which is largely unpredictable and requires evasive action, and the unexpected but predictable (in retrospect) kind.
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Old 17th Apr 2018, 4:54 pm   #7
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Default Re: CPU cooling fan - blind-spots in risk/ personal safety assessment?

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The hole in my fingernail took a long time to grow out since it was right at the base.. i had to renew the superglue repair a couple of times a day to stop the ripped nail catching on things.
Ouch!! That sounds like a very sensitive and very painful location to drill through!


Dave: good point, thatís really hard to do. I do do manage it last week in a more domestic settin.
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Old 17th Apr 2018, 7:15 pm   #8
The Philpott
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Default Re: CPU cooling fan - blind-spots in risk/ personal safety assessment?

Whatever happened, happened very quickly- I think the wire wrapped round the drill bit and pulled my hand towards it. Very stupid, very Reg Prescott.
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Old 17th Apr 2018, 7:20 pm   #9
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Default Re: CPU cooling fan - blind-spots in risk/ personal safety assessment?

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I think that there's a difference between that sort of accident, which is largely unpredictable and requires evasive action, and the unexpected but predictable (in retrospect) kind.
A really good point. A few years ago, I was helping a friend install a shower in a warehouse unit.

I was kneeling on the floorboards and described a reference point from underneath where he should drill through (with a 600W drill)

Seconds later, the drill bit popped through the boards, 5mm from my thigh. It would have been carnage.
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Old 17th Apr 2018, 7:23 pm   #10
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Default Re: CPU cooling fan - blind-spots in risk/ personal safety assessment?

A safety officer once told me (I have no idea if this is true or not) that the machine tool that causes the most accidents is the pillar drill. The point is that people assume it is just a big version of the electric drill they have at home and don't bother to clamp the workpiece, they hand-hold it. And then the drill bit grabs, the workpiece spins round, and the result is obvious (and very unpleasant).
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Old 17th Apr 2018, 11:31 pm   #11
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Default Re: CPU cooling fan - blind-spots in risk/ personal safety assessment?

I think what happens here is, as the years pass, we have less and less injuries in the workshop because over time we have had most of them, cuts from drills, tools sharp metal edges, blisters from filing, trying to catch a falling soldering iron by its tip etc and we simply fall into less traps.

If I look at the scars on my hands, one of the bigger arrays I acquired as a teenager is that from a model plane motor that was resistant to start (and these were intended to be finger started) When it did start, the tip of the prop caused multiple parallel lacerations.
But these are not quite as bad as those acquired from what I thought was a dead parrot that I picked up, of course it was just stunned and when it woke up and put the chompers on my finger, it did quite a bit of damage. Then there are the burns from molten lead that I spilled as a 10 year old, melting down lead head nails in a tin over a fire to make cast replicas of Yogi Bear.

Some of the accidents are just lack of attention & concentration and risk awareness.

I met a fellow who was mowing the lawn with a petrol mower and some flax got stuck around the blade, so he flipped the mower over & reached in to get it out and lost some fingers. He remained baffled as to why he didn't turn it off. Another case, worse, two friends were out fishing with dynamite, they would light the fuse, as it came close to the stick, they threw it in the water, the acoustic wave stunned many fish and they floated to the top. One fellow lit the fuse, was about to throw it in the water, and his friend asked him a question, which distracted him long enough for it to explode.

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Old 18th Apr 2018, 9:09 am   #12
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Default Re: CPU cooling fan - blind-spots in risk/ personal safety assessment?

At least it wasn't bad enough to need a trip to A&E. Motors of any sort can be nasty!

Someone I know needed a stay at the local bandageworks after he'd rebuilt a truck starter-motor and decided to test it by hooking it to a 24V battery with a pair of jump-leads. He was holding the body of the motor as he made the final connection - the inertial reaction of the thing made it leap into the air, smashing bones in his left wrist and shoulder.

And anyone who says they've never knocked the soldering-iron off the bench and instinctively reached to grab it as it falls is fibbing.
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Old 18th Apr 2018, 11:32 am   #13
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Default Re: CPU cooling fan - blind-spots in risk/ personal safety assessment?

Quote:
Originally Posted by Argus25 View Post
I think what happens here is, as the years pass, we have less and less injuries in the workshop because over time we have had most of them, cuts from drills, tools sharp metal edges, blisters from filing, trying to catch a falling soldering iron by its tip etc and we simply fall into less traps.
Well put, Hugo. We do acquire a broader awareness in the increments you describe, not but a perfect one.

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Originally Posted by Argus25 View Post
If I look at the scars on my hands, one of the bigger arrays I acquired as a teenager is that from a model plane motor that was resistant to start ... When it did start, the tip of the prop caused multiple parallel lacerations.
But ...not quite as bad as those acquired from what I thought was a dead parrot that I picked up, of course it was just stunned and when it woke up and put the chompers on my finger, it did quite a bit of damage.
Resilient hands, there, Hugo. I've never had a parrot crush my fingers like a brazil nut, but the lead incident also sounds excruciating. I do remember that kind of youthful zeal to experiment in ways that in retrospect, are fraught with danger.
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Old 18th Apr 2018, 11:37 am   #14
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Default Re: CPU cooling fan - blind-spots in risk/ personal safety assessment?

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Originally Posted by G6Tanuki View Post
Someone I know needed a stay at the local bandageworks after he'd rebuilt a truck starter-motor and decided to test it by hooking it to a 24V battery with a pair of jump-leads. He was holding the body of the motor as he made the final connection - the inertial reaction of the thing made it leap into the air, smashing bones in his left wrist and shoulder.
Quite a lot of torque there! That must have been a surprise as it leapt into the air and collided. Ouch!

Even cordless tools can be very dangerous. I well remember when I first started using a cordless screwdriver/drill, 25 years ago. I had no idea how much torque they could have.

Working outside, I accidentally lowered the cordless, still finger on trigger, so that the chuck connected with loose fabric of my jeans in my upper leg. In an flash, material was wrapped round the chuck and if the thing had turned for a tiny bit longer, I might well have been trying to save a rather priceless part of my anatomy. Fortunately I just walked away with a memorable lesson.
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Old 18th Apr 2018, 12:50 pm   #15
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Default Re: CPU cooling fan - blind-spots in risk/ personal safety assessment?

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It's a reaction that can be learnt, though.
I now 'instinctively' step back if I drop something sharp.
I find I do too - dropping a scalpel, I jerk my foot out of the way. Whereas if it is something fragile, I thrust my foot into place to try to break its fall.

And yes - soldering iron - I seem to have acquired the knack of letting it fall but then immediately grabbing the lead before it starts trying to tin the floor.

Rotating objects - powerful motors - whenever possible, I run up slowly! A 400Hz 3-phase induction motor does get up to awesome speeds!
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