Industrial & Laboratory Safety

The importance of safety and common sense can not be over stressed.  In 25 years there is only one company that I thought had over done safety.  But I will never forget that company and the fact that they over stressed safety.  So, perhaps they did the best job since I'll never forget?  

Since you can not possibly teach someone everything, safety is as much common sense as it is preparedness.  But continued training, study, and practice builds common sense.  

Safety means different things to different individuals.  Very often one person does not feel safe doing what some one else does all the time.  Our people are taught that if they do not feel safe doing something then to stop and give someone a call to discuss it.  Don't do anything that they are not comfortable with.  

We tell our people to stop and think before they do something.  Ask themselves what are the risks and problems that they foresee?  What can they do to minimize risks?

How Do You Stop?

You can have a stop, a pause and an E(mergency)-stop.  

For E-stop -- there are debates as to if you should cut power to only the actuators (controller outputs) or whether you have to cut power to everything.  We usually cut power to actuators and leave power on the inputs and controllers.  For electronics power this is easy, a simple relay, but it must be wired external to all controllers ("hard wired").  You don't want the E-stop going through your controller because if your controller "goes crazy" and you hit the E-stop then you do not want to depend on your controller to recognize the E-stop and stop everything.  Not that controllers typically "go crazy" but with E-stop circuits you are planning for worst case.  You can wire this E-stop power to a controller input so the controller will know the e-stop was pressed.  The controller will figure out something is wrong if none of the outputs are working -- it helps to explicitly tell the controller an E-stop occurred so it is not displaying a lot of errors related to outputs not performing correctly.  

For pneumatics there are "dump" valves that quickly dump the air pressure, and I assume there is the same for hydraulics.  With pneumatics (and probably hydraulics) you have to be careful because if you "dump" all the air pressure then the cylinder may want to return to it's rest position.  If you hit the E-stop, dump the pressure, and then cylinders start returning to their reset position -- that is not good.   Typically three way valves are incorporated so that when you dump the air pressure the cylinder goes to a neutral position. 

Normally for an E-stop you are required to pull the E-stop button back out and then press a "reset" button before power is reapplied to the actuators.  You don't want everything to start flying around as soon as the operator pulls the E-stop button back out.  With an E-stop all parts in use are scrapped, everything has to be "homed", reset,  and reinitialized.  Operators soon learn to use the "stop" button if possible.  The programmer has to be careful because you don't know where anything is but you have to return everything to its home position without crashing anything.  There are special e-stop relays available.  

A stop is -- abort the current sequence and then restart another sequence later.  Power remains on the actuators.  You can have immediate stops or stop when the current step or sequence is completed.  Assuming that a sequence is a series of short steps where each step only requires a few seconds, it is easier to program to stop at the end of a step or at the end of a sequence (or cycle). 

A pause is -- stop the sequence and then resume where you left off.  Power remains on the actuators.  This is difficult to program correctly.  There are beautiful applications where the machines pause when you stick your hand in the light curtain and then resume after removing your hand.  This is great for operators (they love it) but expensive, difficult to program and hard to get to work 100% correctly.  It can be done -- just more programming and testing which means more $.  

For a stop and a pause you have to consider how fast do you want something to stop?  For something with a large mass (inertia) you might have to use braking.  Other cases you can just let them coast or decelerate to a stop.  With something like a big press where you build up incredible amounts of inertia -- I don't know how even braking could quickly stop a press in the event of an emergency. 

Machine Guarding

For machine guarding the most common ways are lexan, light curtains, mats, and palm buttons.  The lexan type windows have switches on them so you can tell when they are in place or removed.  The light curtains are nice but expensive.  When you stick your hand (or anything else!) in the light curtain, it closes a contact which tells the system to stop or pause.  Safety mats are placed around the machine and when someone steps on the mat a contact is closed telling the system to stop. 

The palm buttons are a pair of buttons that require the operator to have their hands on the buttons for the machine to operate.  You assume that their hands are not in the machine.  Operators try to place heavy objects on the palm buttons so their hands can be free.  Therefore you require (logic in your controller) that they remove their hands between sequences so that operators can not simply set something on the buttons.  There are now optical "palm buttons" where the operators rest their fingers in a cup -- instead of holding down push buttons.  

Watch Dog Timers

There are devices known as "watch dog timers" that are great for detecting unforeseen events.  They are typically external to the control system and are configured so that the control system must pulse them every X seconds (where X is configurable).  Every time the control system sends a pulse -- it resets the watch dog timer.  If the control system does not reset the timer before it times out THEN the watch dog timer closes a set of relay contacts that be connected to anything -- your e-stop circuit, stack lights, horns, etc. 

Some watch dog timers are boards that plug into your computer and will automatically reset your computer if the timer times out.  There are watch dog timer output modules that sit in your I/O rack that will sound an alarm if you lose power or communications with the controller. 

Safety Links

• Applied Robotics -- safety mats and light curtains
• Bender  -- Ground Fault Monitoring & Ground Fault Protection Equipment
• Berkshire Products -- PC based (internal) watchdog timers
• Brentek -- watchdog timers, great applications note
• BRight Safety Training & Consulting --  Health and safety training certification courses & professional consulting in the Toronto, Canada area. 
• Business & Legal Reports -- compliance and employee training materials
• B&B Electronics -- watchdog timers
• Cedes -- light curtains, safety relays, safety sensors
• Champion America -- signs and safety supplies
• Conney -- safety products
• Dolan-Jenner -- light curtains
• Emed -- signs and safety solutions
• Vallen Safety Supplies  -- safety supplies
• Force Guided Relays -- manufacturer/distributor of electromechanical safety relays with force guided contact sets
• Frost Controls -- light curtains
• Galeton Gloves and Safety Products -- quality work gloves, safety glasses and footwear, dust mask respirators, first aid supplies, protective clothing and equipment and other safety products
• Grainger -- large selection of industrial safety & security products
• Honeywell Data Instruments -- light curtains
• IDCWare -- OSHA safety training software
• J.J. Keller & Associates -- Safety and regulatory products, training and services for transportation, manufacturing, construction and general industry
• Keyence -- light curtains
• K-TEC   -- sensitive ground-fault protection products and electrical safety
• Lab Safety Supplies   -- laboratory, industrial, and safety supplies
• Leonard -- safety equipment
• Libra Industries  -- supplier and recycler of safety products
• National Safety Compliance  -- Safety videos, software and resources for OSHA compliance
• Neosafety  -- environmental health and safety marketplace offering a full complement of supplies, software and web-based training solutions
• Omark Safety -- over 20 major categories of safety products, each with multiple sub-categories, on-line ordering
• Omron -- safety light curtains, limit switches, E-stop buttons, relays
• Pearlweave  -- safety netting
• Pinnacle Systems -- light curtains, mats, palm buttons
• Pressroom Electronics -- press automation controllers and punch press safety controls for OSHA compliance
• Recora -- safety mats
• Safety & Construction Supply  -- personal, industrial, traffic control and fleet/utility safety products
• Safety Advantage  -- safety videos and training for the workplace
• Schmersal -- Safety Interlock Switches
• Scientific Technologies -- light curtains, interlock switches, relays, mats, palm buttons
• Seton Identification Products -- safety & identification products
• STI machine safeguarding solutions
• Texas America Safety Company  -- Distributors of Occupational Safety Products and Safety Supplies
• The Safety Standard -- reference materials, training programs, signs & facility marking, forms, equipment & hardware
• Triad Controls -- light curtains, mats, palm buttons
• Wear Guard -- industrial clothing and safety apparel

We try to offer a fair and balanced opinion on every page of our website.  We would appreciate more information from other users to express their opinions which we will then incorporate.  If you have questions or comments please post them on our message board (see button in left hand column) so that others can read and benefit.