Forensic Clues Issue 82: What Causes Industrial Accidents?

Inadequate Guarding / Design Flaws

The most common cause of machine guarding accidents is due to inadequate guarding that is the result of design flaws.  There are many reasons for this, but one of the most frequent, and avoidable, is due to people designing and manufacturing machinery that are not licensed engineers.  Engineering education provides guidelines rooted in science and over a century of experience with industrial machinery, including ensuring adequate strength, operation, programming, and guarding of machinery, while incorporating human factors considerations that are essential to ensure a machine is safely usable by humans.  Professional engineers are engineers that have met experience requirements as well as     passing two very in-depth examinations, one covering the entirety of an individual’s engineering education, the final licensing examination involving complex problems and inadequate information that test an engineer’s ability to problem solve without knowing all of the variables.  In fact, some state laws prohibit anyone from using the label “engineer” unless they have become a licensed professional engineer.  Despite this, there is rampant use of this label for anyone filling the role of maintenance or design, regardless of experience or education.  Specialty machinery is often manufactured by individuals with decades of experience in a specific field.  While their experience helps them make a machine that gets the job done, the author has seen too many times that there is complete ignorance and dismissal of safety concerns, meeting industrial standards, or adapting to human behavior.  This results in machines that are guaranteed to cause accidents, if they haven’t yet, they will.  Even if a machine is designed     appropriately, there can be deviations from the design of the machine, resulting in an unsafe machine.  The crux of these situations is determining when the deviation occurred, and who is responsible. 

Bypassing Safety Devices

Bypassing machine safety devices is something that can usually be prevented with optimal hazard assessment and design of the safety systems and safeguards.  Modern computer-controlled machinery combined with limit switches that incorporate safety guard locking offer advanced safety that provides optimal protection.   Even with these systems, things can and do go wrong, at times due to design flaws, wiring errors, programming errors, or potentially still the bypassing of safety devices.  Many of these    interlocking limit switches with guard locking do have an override key which leaves room for human    error.  Human nature along with the need to have high levels of industrial productivity leads to trying to do operations in the quickest, easiest manner.  If it is possible to bypass a critical safety device that slows the process down more than operators are willing to tolerate, some operators will choose the path of least resistance.  This quickly leads to an unsafe machine that will eventually lead to an accident. 

Maintenance Procedures

Maintenance of machinery presents additional challenges not seen during normal operation.  Maintenance often involves accessing hazardous areas of the machinery not normally accessed during normal operation.  Machines can be designed in such a way to usually make maintenance procedures safe, but there are situations where maintenance or cleaning operations will put the individual exposed to greater risk and hazards.  Many accidents result during cleaning cycles of machinery that involve people, especially when the cleaning crew are cleaners instead of machine operators, with reduced knowledge and awareness of machine safety, hazards, and operation.  Industry Standards including the ANSI B11   series identify hazard assessment methods and required safety criteria that has to be met to be in compliance with these voluntary standards.  Following proper lockout/tagout procedures are often critical to getting repairs completed on machinery in a safe manner.  This ensures all machine motion is stopped, and locked to prevent accidental re-activation, which is necessary as many machines are large enough to prevent having visual contact with all areas of the machine from the operator’s console. 

Failure to Maintain Safeguards

Safeguards must be maintained to ensure proper functionality and to ensure the safeguards are operating according to original manufacturer's specifications.  If the machine is designed to be failsafe, this ensures safeguards don’t fail unnoticed.  The problem is that companies that prioritize productivity over safety may sacrifice safety for higher rates of productivity.   Barrier guards can get damaged by impacts from other machinery or vehicles, which can result in hazards becoming accessible to machine operators.     Systems that are not failsafe become increasingly less safe with each safeguard element that fails. 

Not Making Machine Safeguards Failsafe

Failsafe is a concept where if there is a failure in a machine, or in the machine safety systems, the machine fails in a safe position.  This is in contrast to a non failsafe machine, where a failure of a critical safety element could do undetected and continue to allow the machine to operate.  An example of a type of failsafe is found in historical automobiles where the car could not be started unless the seatbelt was buckled.  This prevented car operators from driving without a seatbelt, although it is clearly not 100% failsafe in that some drivers may have buckled the belt, and sat on it versus wearing it.  A failsafe guard would include a guard locking limit switch that will stay locked in the event of a failure of the limit switch.   An example of when a safety system is not failsafe:  Light curtains are used in applications requiring frequent operator interaction.  They detect a person crossing the safety boundary, and will shut down power to the machine and bring it to a stop.  If a light curtain is not failsafe, the machine keeps running, without this critical safety feature, which would also be unknown to the operator.  The likelihood of an accident occurring in this situation where the operator expects the machine to shut down if they make a mistake increases exponentially. 

How We Can Help

At MASE, we are licensed professional engineers, with experience in using all available evidence to identify the cause of accidents.  Call us at (855) 627-6273 or email us at info@mase.pro to discuss your accident case.