Safety Best Practices for Computer Work

[horusfalcon]

I figure I'm going to get a lot of discussion here, so let me set out why I felt moved to start this thread.  There are a lot of guys here who do computer work who have a less than optimal working environment (e.g., their kitchen table).  I wanted to talk about work safety practices for the benefit of the community so that no one we know and love gets hurt or killed working with electrical equipment.

It's worth noting that 110vac single-phase "house current" has killed more people than any other form of electrical power.

Let's make some BASIC ASSUMPTIONS:

• 1.)  We are not working in an electronics shop environment with a fully equipped workbench, static mat, and a large array of test equipment.  (We'll presume most folks are working on the nearest convenient sturdy table.)
• 2.)  Nothing more sophisticated than basic hand tools, and maybe a soldering iron and multimeter and various "shop aids" as described are used during the work.
• 3.)  The work in question can be anything from a full-blown build to repair, upgrade, or routine cleaning and maintenance.

BASIC WORK AREA PREPARATIONS:

With these assumptions,  let's proceed with getting ready to work.  The first steps are to set up the work area and plan your work.  There are a few things which can be done to enhance the work area's effectiveness and safety:

1.)  Clear off the work area.  Get rid of anything not directly related to the work at hand.  Especially remove any loose objects, foods, or liquids which might get in the way of the work.  If you smoke while you work, have a heavy ash tray or butt can (a coffee can with some sand in it) near the table to control any cigarettes, cigars, etc. when not in use, and use it.  (A cigarette end can reach temperatures approaching 1600 deg F.)  

2.)  Clear enough workspace to be able to approach your work from as many angles as possible.  

3.)  The table or surface you are using should be stable and sturdy enough to support the weight of all the components you will be working on.

4.)  Check to be certain that receptacles for power are close enough at hand to be useful.  If this is not the case, move the table closer to them, or run an extension cord (being careful to route it to minimize tripping hazards).  The last thing you want is power cords festooned all over the place.  

5.)  Consider having at least one power strip available with a "master off" switch.  This gives you a safety "kill switch" that is close at hand if things go wrong.  (Work on the gear long enough, and it will happen...)

6.)  Once the work area is clear, put down a clean, dry cloth or vinyl table covering.  (I use an old white sheet from a twin bed set we no longer use - makes a bright, clean work surface that helps keep screws and other fasteners from bouncing or skittering across the table, and makes them easier to find when dropped.  It also help when laying out cables, fasteners, and other components prior to a build.)

7.)  Stop for a moment if you have not already planned out your work and do it now.  A work plan doesn't have to be a big deal, just a clear idea of what you're setting out to accomplish, how you intend to go about it, and what you will need to get the job done.

8.) Gather your tools, materials and components, and arrange them in a logical manner that facilitates your work plan.

9.)  Provide yourself with a means of grounding any systems on which work is to be performed.  This is very important, and should be done carefully.  I'll cover some ways to do this effectively and safely without breaking the bank further on.

10.)  Consider obtaining and using a pair of safety glasses whenever testing or operating a computer on the work table with the case open.  (A cheap pair of clear, non-tinted safety glasses can be had for under $6.00 US.  Small investment when you consider what could be at stake.)

ELECTRICAL SAFETY:

There are some basic considerations for electrical safety when doing computer work.  Electrical energies found in 110 vac current have sufficient force to be deadly to the human body, and to cause personal injury or equipment damage if improperly used.  The first rule of Electrical Safety is:

1.)  Always work with the power OFF whenever possible, especially when doing cold-pluggable component replacement/removal, or routine cleaning, repairs, or maintenance.

If you cannot work with the power OFF, remember:

2.)  Before starting any work, move pets and small children away from the work area for their protection and yours.

3.)  If working in LIVE EQUIPMENT for testing or troubleshooting, wear eye protection, and remove all jewelry, watches, and other metallic objects from your person before starting work.  That means out of your pockets, off your fingers, no wristwatches, necklaces, etc.  Wear shoes with solid soles, preferably good rubber soles that will insulate you from ground.

4.)  If working in LIVE EQUIPMENT, make sure you are NOT ALONE. Whoever is there with you needs to know how to kill power to your worktable if the need arises, and be able to get past you to safely pull the plug.  PLEASE brief your "safety buddy" before starting work so they know you are working and need them there.

STATIC ELECTRICITY & GROUNDING:

Most folks who do computer work to any degree have heard the warnings about static electricity being potentially damaging to delicate electronic components in a computer or other device.  Most also know that grounding oneself helps get rid of static electricity.

Static electricity is not the primary reason systems are provided with a ground wire, though.  Grounding a piece of equipment provides an "emergency path" for current to flow in the event of a short circuit.  To use a technical term, it places the equipment at "ground potential"  so that if a short occurs, the equipment's case and ground lead provide the quickest path to ground for the misplaced energy.  This keeps YOU from becoming that path to ground.  It's for your safety, and the safety of the electrical system providing the power.

I've heard it said on more than one occasion that leaving a computer plugged in but "OFF" while the case is open protects it from static discharges.  While that is true, it does not totally de-energize the equipment. It also lays open the possibility of inadvertently powering up the equipment.  

Some motherboards and power supply components need to be discharged before doing any removal of parts or connectors, and this cannot be done with the power cord plugged in.  To this end, we will talk about proper grounding methods that make the computer truly safe to work on.

GROUND LEAD:

WARNING:  a basic understanding of electricity and receptacle wiring is needed to build this and the Grounding Cord which follows.  If you do not possess these skills, enlist the help of a competent, qualified person to do it for you.  Mistakes in making up grounding connections can be fatal.

A ground lead is simply a length of stranded, insulated wire with a ring lug on one end for attachment to a grounding point, and an alligator clip for connecting to the case of a computer or other piece of equipment.  It's easy to make one using a crimp-on lug and an alligator clip that either screws or solders on to the opposite end.  About eight feet of wire is usually more than enough to reach.  To make this ground lead really mobile, bolt the ring lug to the ground tab on a 2-wire to 3-wire AC adapter and plug it in to a regular receptacle.  This will provide you with a ground lead which can be moved or carried in a toolbox for "house calls".

EDIT:  Whoops!  When using a ground lead with a 2/3-wire adapter, DON'T forget to also leave a small lead to lug off the ground terminal to the receptacle ground.  The adapter will only have two prongs (I had this backward in my head for some reason while writing... sorry!)  A better way might be to make the lead up to a conventional 3-wire plug's grounding screw.

GROUNDING CORD:

A grounding cord is made from a regular IEC-style PC Power cord, and a three-pronged male "valise" plug  (available at a local hardware store or electrical supply house for a few dollars).  Cut the molded on male end from the power cord, then dress the outer jacket back about two inches.  Inside are three wires, in the colors white, black ,and green.  Cut off the black and white wires close to the end of the jacket, and strip about 1/4" to 3/8"  of the insulation from the end of the green wire.  Slip the rear shell of the plug over the cord and far enough back to clear the working end, then connect the green wire's stripped end to the grounding screw on the male plug body and assemble the rear shell and strain relief over it.

What you will wind up with is something that looks like a power cord, but does not provide power, only a ground lead.  This can be plugged into a computer on your work table and then to a receptacle to provide it with a safe path to ground without providing it power.  (This is handy for those computers which require the technician to press the power button to discharge stored energy to kill a "Standby LED" on the board before doing any work...)

This post is getting rather long, so I'll stop here, and let the discussion commence.  I invite all who read to participate, and to point out any flaws in the methods and procedures I mention thus far.

Thanks for reading.  Let's work together safely.

Later On,
D

[menotu]

NOW you tell me!     

Some good points horusfalcon - thanks for posting.

[horusfalcon]

NOW you tell me!     

Some good points horusfalcon - thanks for posting.

As an electronics technician/instrument technician/low-voltage electrician and a certified A+, the topic of Safety is one near and dear to my heart.  I could have written a lot more, but thought that was sufficient to start the discussion.  Add a few tips of your own - I'm sure you do certain things a certain way to make it safer without even realizing it.

All it takes is an instant to change a technician's life forever.  I've been fortunate to have learned most of my lessons from others, and to have survived those few personal lessons of my own without severe injury.

Let's share those safety tips, spread 'em around, and help everyone work more safely.

Later On,
D

[lysar]

Very good tips. I especially like the idea for grounding your box without it being hot. Now, if I could just ground my kids without them getting hot...

[Bald Brick]

Good advice, horusfalcon.

I actually managed to zap a chip with static electricity in 1984, and that made me bit more cautious about grounding myself. But do you mean that shutting off the power on a power strip with a "master off" switch will also shut off the connection to the ground? For all these years I've just shut off the power in the belief that the computer was still grounded.

[horusfalcon]

Good advice, horusfalcon.

I actually managed to zap a chip with static electricity in 1984, and that made me bit more cautious about grounding myself. But do you mean that shutting off the power on a power strip with a "master off" switch will also shut off the connection to the ground? For all these years I've just shut off the power in the belief that the computer was still grounded.

No, I didn't intend to convey that - sorry if that's how it came off. A properly made power strip will maintain ground connection and interrupt at least the "hot" side of the line.  Grounding connections are supposed to be maintained through power strips at all times for safety.  (It's easy to check if you know how to use a multimeter....  If it does break the ground, get rid of it!)

Basically, all I wanted to suggest was that the master switch would interrupt line power quickly in the event something went wrong (like, say, a system doesn't POST, or sparks fly on power-up.)

Yep, I've zapped a few chips with static myself.  At work, when I do electronics stuff, I wear a corona discharge bracelet - no wire to connect means lots of freedom of movement.  They're cheap these days (about fifteen bucks) and work pretty well if worn for about 15 minutes prior to starting work.  One thing for our wider reading audience:  Always do static sensitive work with the POWER OFF.  It's better for you and the equipment that way.  (I figure you already knew that, Bald Brick.)

Later On,
D





 

[Yankee]

This isn't a computer but just for example:

There's a Sherwood 100 watt/channel stereo receiver I can get for $99

It has specs equal to some audiophile equipment that used to cost
$500-$600

I suspect it has a little round regulator somewhere on the main circuit
board where you can actually turn the wattage down, but it has to be done
with the power on,  so you can see the setting desired take place per the
meter on the front panel.   Or turn it off and on between settings.

So if I have 60 watt 8 inch 3/ways and want the max output to be 50 watts
you can actually do so.   Even 25 watts output is very adequate for the system
for full volume, and to protect the speakers, etc..  but 50 watts should be a
good setting adjustment then for the amplifier.

You won't get killed but get stung quite severely if you touch something
other than that little round regulator's very top hole with the power on.
You would advise against.   More voltage than watts I guess.

Then you can use the receiver all the time knowing 50 watts would the max
output it can do, and safely do so for the equipment.

I don't know if a CPU or anywhere in a computer has those but they could,
so just an example about it.   Power Off the best advise, of course.

regards,

FF

[horusfalcon]

This isn't a computer but just for example:

There's a Sherwood 100 watt/channel stereo receiver I can get for $99

It has specs equal to some audiophile equipment that used to cost
$500-$600

I suspect it has a little round regulator somewhere on the main circuit
board where you can actually turn the wattage down, but it has to be done
with the power on,  so you can see the setting desired take place per the
meter on the front panel.   Or turn it off and on between settings.

{remainder snipped for brevity}

Sure, there are going to be occasions where it is more practical to work with the power on.  For something like that, hit a local electronics supply store and obtain a set of cheap TV Tuner tools - they're non-conductive plastic and made for adjusting pots and trim caps without interfering with a TV's tuner electromagnetically.  (These might be getting harder to find with the advent of flat-panel TVs, though...)  They also give you that extra bonus of being non-conductive, so they're safer to use if you slip out of the slot.)

If you can't find them locally, try online.  One good source for such tools is GC Electronics out of Rockford, IL.  They've been around for decades now, and are a reliable and expert resource on all things electronics repair-related, very friendly to the electronics hobbyist and professional.

Full Disclosure:  no, I don't work for or have any other affiliation with GC Electronics except as a satisfied customer.

As with a lot of jobs, the right tools can make such a difference.

Later On,
D

[ThirdOfSix]

My number one rule when working around any electrical equipment is to control your reflexes.

Any time you drop ANYTHING, freeze, watch and listen. Never try to catch the falling item! This rule applies as much to a small screw as it does to a pair of pliers.

The same thing applies to reacting to sudden noises etc. Even if someone is shooting at you, if you are working on electrical equipment, freeze first, think second and then react.

If you are working on line voltage or higher equipment or circuits capable of delivering more than about ten amps if shorted to ground, do not wear rings, bracelets, or watches.

When working on something with a high current power supply like some desktop computers or servers, wear eye protection. There were some units that used connectors that even though keyed, could be forced on backwards by someone who was both determined and ignorant. This could cause sparks of molten copper or electrolytic capacitor innards to come flying at the eyes.

Always treat any wire or cable or terminal as though it were hot!

One of the first things to be done when working on solid state electronics is to look at the circuit board or case when you first open it up and determine where you can access the chassis ground/earth lead.

Then, with one hand only, touch that point with a knuckle or the back of a finger such that any static charge differential between you and the unit under repair is neutralized. This technique was in use buy technicians long before someone decided to start selling grounding straps.

If done religiously both on the unit under repair and any sub-assemblies which are picked up to be installed, you will never damage any circuitry from static electricity.

[horusfalcon]

You raise some good points, and some where I believe there is room for improvement...  hope you don't mind the feedback.

My number one rule when working around any electrical equipment is to control your reflexes.

Any time you drop ANYTHING, freeze, watch and listen. Never try to catch the falling item! This rule applies as much to a small screw as it does to a pair of pliers.

So far so good... but better not to have metal tools or fasteners in hand inside energized equipment in the first place.

The same thing applies to reacting to sudden noises etc. Even if someone is shooting at you, if you are working on electrical equipment, freeze first, think second and then react.

That "shooting at you" is for emphasis, right?  I've only been shot at once while working on a radio set, and that was an exercise, so blanks. (I "died" during the exercise... )

Again, better not to have metal objects in hand inside energized equipment.  (And better still not to work on energized equipment unless absolutely necessary.)

If you are working on line voltage or higher equipment or circuits capable of delivering more than about ten amps if shorted to ground, do not wear rings, bracelets, or watches.

As little as 100 milliamps can kill you.  Treat all live circuits with the respect they deserve.  If you're in energized gear, remove all metal objects from your person (stow then in a pocket or pouch below the waist or in a separate location, like your toolbox).  After death, there is no practical way of knowing precisely how much current killed you.

When working on something with a high current power supply like some desktop computers or servers, wear eye protection. There were some units that used connectors that even though keyed, could be forced on backwards by someone who was both determined and ignorant. This could cause sparks of molten copper or electrolytic capacitor innards to come flying at the eyes.

You raise excellent points here:  DO wear eye protection - I'd advocate wearing it in any energized equipment.  (It only takes a small part going pi-yow! to create a piece of molten slag that could damage an eye.)   

The other point is this:  If it doesn't fit DON'T force it... damage of one kind or another will inevitably result.  Take your time, examine the connectors, and spot the problem, then proceed.

Always treat any wire or cable or terminal as though it were hot!

This goes to safe work habits, and is good advice.  I tend to be a bit more relaxed and say treat everything as hot until you have verified it is isolated and dead (that means the circuit is verifiably open and you have put a voltmeter/multimeter on it to check it to ground), but this is a good way to go here.  Get in the habit, and you'll be in a better safety posture.

One of the first things to be done when working on solid state electronics is to look at the circuit board or case when you first open it up and determine where you can access the chassis ground/earth lead.

Absolutely!  This is an excellent practice.  In most cases, the case of a computer is bonded to the power supply ground, but it's good to know that for sure going in.  If in doubt, get a multimeter, learn to properly use it, and check.  (Good meters can be had for under $20 these days...)

Then, with one hand only, touch that point with a knuckle or the back of a finger such that any static charge differential between you and the unit under repair is neutralized. This technique was in use buy technicians long before someone decided to start selling grounding straps.

If done religiously both on the unit under repair and any sub-assemblies which are picked up to be installed, you will never damage any circuitry from static electricity.

That "religiously" part is where some folks (myself included) have trouble.  Being of, erm, high body mass index, I tend to store high static charges very rapidly when the air is dry.  I just put on my bracelet and I'm good.

That "back of the hand" thing is an old electrician's trick:  the back of your hand is less sensitive to temperature, and using the back of the hand instead of the palm allows your natural reflex to pull you away if a surface is energized.  Touch it with the palm or your fingertips, and your reflexes tend to cause you to grip tighter (thus making a better circuit so you fry more quickly).

Some good info.  Thanks for sharing with everyone.  The whole aim in view is to talk about this so we can learn from each other.  Let's keep it going, folks.

Later On,
D






[/quote]

[Yankee]

Sure, there are going to be occasions where it is more practical to work with the power on.  For something like that, hit a local electronics supply store and obtain a set of cheap TV Tuner tools - they're non-conductive plastic and made for adjusting pots and trim caps without interfering with a TV's tuner electromagnetically.

Great idea, THX.   Funny, even a toothpick would turn the little thing.
Probably shouldn't try that either.
Always a better way to cook an egg around here.

regards,

FF

[ThirdOfSix]

horusfalcon,

You keep interjecting that one should not be using metal tools while working on live equipment.

You seem to have missed my second rule about treating all equipment as if it were live.

I defy you to cut most wire without a metal tool or remove mounting screws with a non-metal screwdriver.

My comments about rings etc falls in the same category and my qualifiers about potential amperage if a circuit is shorted by said ring has nothing to do with potential for electrocution.

It has to do with the fact that a ring across a high amperage circuit which turns out to have been live even though you thought it wasn't, can instantly turn red hot or white hot and become part of what is left of your finger.

The voltage part of the qualification has to do with the fact that normal skin resistance limits current through the human body to a non-lethal level at anything below about fifty volts even though most people have been brainwashed by Hollywood physics to believe otherwise.

In the case of a ring, your body sweats and the interface between the ring and your body will be damp with salty sweat which effectively eliminates the factor of skin resistance in limiting the current passed to the low resistance internal tissues of your body.

When I last checked, the specification for ground fault circuit interrupters was to trip at seven milliamps.

Also, the comment about not grabbing for a dropped item has nothing to do with whether that item is made of metal. While reacting in a reflexive fashion, a person is quite likely to put their had where it should not go. This could result in shock or in damage to an expensive part of the equipment being worked on. Even worse and most probable according to Murphy's law, you are likely to end up batting the item across the room where you will never find it.

No, the comment about "even if being shot at" was not for emphasis only.

I spent eighteen months in Vietnam during the war and one of the systems that I worked on was a radar system which had a power supply capable of providing many kilowatts of power at several thousand volts. To lose concentration and attempt to dive to the ground without thinking first as an infantry guy was taught could very well have a person inadvertently get across that circuit.

This could mean instant and certain death. Bullets, rockets, and shrapnel are quite likely to miss you but electrons never miss if you are careless.


So, you see, the rules that I have lived by are habit that if followed until they become automatic will save lives because even if a person starts working on a live circuit without realizing it, he will not do anything which will get him killed.

And I agree that "religiously" was not really the proper word when I should have said "subconsciously" or "habitually".

I do see your point about static electricity and the size of the person. I am small so I do not make as good of a charge reservoir as a larger person would.

[horusfalcon]

Hey, man, I didn't mean for this to get personal.  As long as we can have open and honest discussions about the topic, sure, let's go back and forth.  Everybody reading learns more that way.

horusfalcon,

You keep interjecting that one should not be using metal tools while working on live equipment.

You presume my comments are directed solely at you - that is not the case.  We are both speaking to a wider audience who may not have chewed the same ground as you and I have.  The discussion is for everyone's benefit.

You seem to have missed my second rule about treating all equipment as if it were live.

No, in fact, my first sentence in reply to this idea was, "This goes to safe work habits, and is good advice."  After that, I was stating a personal preference, but one I believe is backed up by established best practices for electrical safety.

I defy you to cut most wire without a metal tool or remove mounting screws with a non-metal screwdriver.

And why would you want to do these things to a computer sitting on your kitchen table??  Battlefield practices are different because they have to be, but we're no longer in combat here, man.  Ease up a little, and take the safer path.  Don't work hot if you don't have to.  (There are far fewer situation where one really needs to break the plane of the cabinet with the gear energized in a computer than are generally acknowledged.)

Aside for a moment:  I was in the Navy in the submarine force for most of six years of active duty, and in the National Guard as a radio & telephone specialist (31V) for eight years.  Not quite the same as your Vietnam service in-theatre (which, thanks for doing your part, man - much respect.)

My comments about rings etc falls in the same category and my qualifiers about potential amperage if a circuit is shorted by said ring has nothing to do with potential for electrocution.

It has to do with the fact that a ring across a high amperage circuit which turns out to have been live even though you thought it wasn't, can instantly turn red hot or white hot and become part of what is left of your finger.

You are entirely right that electrocution is not the only hazard.  The effect you describe here is indeed a real hazard to the technician.  I did not mean to imply electrocution was the only hazard - perhaps I should have phrased that differently.  Still, I think we can agree that less metal on the body, less metal on the hand, means a safer presence in energized equipment?

The voltage part of the qualification has to do with the fact that normal skin resistance limits current through the human body to a non-lethal level at anything below about fifty volts even though most people have been brainwashed by Hollywood physics to believe otherwise.

In the case of a ring, your body sweats and the interface between the ring and your body will be damp with salty sweat which effectively eliminates the factor of skin resistance in limiting the current passed to the low resistance internal tissues of your body.

Yeah... the point is that you're going to have no idea what you've touched in terms of its voltage or current capability until it's too late.  Again, better not to work in energized equipment unless absolutely necessary for troubleshooting, testing, or adjustment (not too much of that in computer gear).  We can minimize the risk most by minimizing our exposure to live circuits.

When I last checked, the specification for ground fault circuit interrupters was to trip at seven milliamps.

I don't dispute this.  In fact, this is well below the minimum threshold for electrocution.  Not a bad idea to use one if you have one available (and they're not all that expensive, considering the alternative).

Also, the comment about not grabbing for a dropped item has nothing to do with whether that item is made of metal. While reacting in a reflexive fashion, a person is quite likely to put their had where it should not go. This could result in shock or in damage to an expensive part of the equipment being worked on. Even worse and most probable according to Murphy's law, you are likely to end up batting the item across the room where you will never find it.

You are quite right, though a dropped metal object will almost certainly cause as much if not more damage to the equipment as a misplaced hand, the potential damage to the technician is as great in either case.

No, the comment about "even if being shot at" was not for emphasis only.

I spent eighteen months in Vietnam during the war and one of the systems that I worked on was a radar system which had a power supply capable of providing many kilowatts of power at several thousand volts. To lose concentration and attempt to dive to the ground without thinking first as an infantry guy was taught could very well have a person inadvertently get across that circuit.

This could mean instant and certain death. Bullets, rockets, and shrapnel are quite likely to miss you but electrons never miss if you are careless.

Thanks again for your service.  Remember that our discussion is not about battlefield practices.  I do seem to remember agreeing that not giving in to your reflexes is a good idea.  If anything, a computer's case is more crowded than that of, say, an SPS-10A Radar Set (which I worked on briefly in the Navy).

So, you see, the rules that I have lived by are habit that if followed until they become automatic will save lives because even if a person starts working on a live circuit without realizing it, he will not do anything which will get him killed.

Sure.  I get that.  It sounds like we had similar training, but we weren't talking about military gear in a tactical environment.  At home, on a workbench or table, I would contend that not working on energized equipment when you don't absolutely have to is still the best way forward.

And I agree that "religiously" was not really the proper word when I should have said "subconsciously" or "habitually".

I didn't actually take issue with the word, so much as what it implied - just doing something because it is a habit or a ritual.  There are times to wear anti-static gear, and times when it's the last thing you want on.  Knowing when anti-static gear is not appropriate (e.g., inside live equipment) is just as important as knowing when to wear it - that's all I was trying to get across.

I do see your point about static electricity and the size of the person. I am small so I do not make as good of a charge reservoir as a larger person would.

Yeah... I've toasted my share of CMOS that way.

Thanks for participating, and for tolerating my feedback.  The aim in view is to make everyone's work practices safer.  Hopefully, working together we will all learn from each other.

Later On,
D

[horusfalcon]

A big ol' OOPS here in my original post:  I edited that, but it's significant enough to warrant a separate post, too.

EDIT:  Whoops!  When using a ground lead with a 2/3-wire adapter, DON'T forget to also leave a small lead to lug off the ground terminal to the receptacle ground.  The adapter will only have two prongs (I had this backward in my head for some reason while writing... sorry!)  A better way might be to make the lead up to a conventional 3-wire plug's grounding screw.

Don't know what I was thinking that night....

Later On,
D

[Tony]

Great Thread idea, thanks horusfalcon. Great discussion area also.

One point I was taught when studying Electronics and Computer Engineering / Workshop: when working on a "Live" circuit, which is one of the more Dynamic of situations, have one hand in your pocket.
Our Supply in Australia is 240V AC, 50Hz.

6 milliamps (0.006 Amps)  across your Heart can Kill you.

The idea is; if right handed put your left hand in your left pocket, work with your right hand. The current if you do hit it will be re-directed down your left leg to ground, rather than across your chest, and Heart.
This is for a workbench situation, like working on a Live Circuit, i.e. Computer, T.V.