Safety Hierarchy, Hierarchy of Controls & Haddon’s 10 Countermeasures & Warnings

Engineering Tools Provide Solutions to Long Standing Boat Propeller Safety Issues

Two ostriches with heads in sand

Two ostriches with heads in sand

The boating industry repeatedly just sticks it head in the sand regarding long standing propeller safety issues. We suggest its time to go back to the drawing board on Perpetual boat propeller accident scenarios, like the Perpetual Propeller Accident Scenarios identified in a related post. Effective, practical, economical solutions need to be identified, tested, commercialized, and deployed.

Plenty new solutions remain to be discovered. Some effective, practical, economical solutions have long rejected by the boating industry. New materials and technologies are constantly placing more tools in our tool belt. One resource often overlooked, are solutions to similar problems in other industries.

We hope the tools below aid all those addressing long standing boat propeller safety issues.

The Safety Hierarchy

The Safety Hierarchy defines the sequence of steps used by product design engineers and safety professionals to prevent injuries once specific hazards are identified. In its simplest version the process is to identify the hazards of use, potential misuse, and of the environment in which the product is to be used.
     1. Design,
     2. Guard, and
     3. Warn.

When a hazard is identified, the best thing to do is to design out the hazard. By removing the hazard the danger no longer exits.

If it is not feasible to design out the hazard, the next best step is to guard against the hazard. Guards are physical barriers between people and the hazard. People that cannot come in contact with the hazard cannot be injured by it.

If guarding is not practical, the next best step is to warn of the hazard. Warnings require numerous actions of the person being warned to be effective. As a result, warnings are much less effective than designing out the hazard or the use of guards. Thus warnings are last step in the safety hierarchy as it is presented in its most basic form.

The three step Safety Hierarchy above is often presented with two more steps:

4. Training
5. Personal protective equipment (PPE)

Training and personal protective equipment are often used in manufacturing operations where someone has administrative control over the workers. Factory employees receive training /instruction, and protective equipment (such as eye shields, hearing protection, gloves, steel toed boots, respirators).

Some versions of the Safety Hierarchy re-write step 3 as “Guards and interlocks”, adding the use of safety interlocks to the process.

The Safety Hierarchy In The Courtroom

If you manufacture almost any mechanical product and are taken to court in a product liability or injury law suit, you will likely be asked about the basic 3 step Safety Hierarchy (Design, Guard, Warn). You will be asked if you identified this hazard and why you to addressed it in the manner you did, which may be not at all.

If you chose to use warnings while your competitors chose to design out the hazard or to guard against it, you will be uncomfortable in that setting.

All major marine drive manufacturers are well aware of this fact.

The industry defends their non-use of propeller guards and certain propeller safety devices that appear to be logical extensions of the Safety Hierarchy by:

  • Saying, “Our product cannot be dangerous because it meets industry standards”, referring to voluntary ABYC standards.
  • Following in lockstep with each other on safety issues, no manufacturer adds significant propeller safety devices unless everybody does at once. In general we just see them all oppose the same things.
  • Saying solutions proposed by others have problems and cause unintended consequences
  • Saying no standards exist for the solutions proposed by others (ABYC does not issue standards for devices the industry does not approve of)
  • Saying the proposed solutions were not available off the shelf in the exact size and model needed at the time this product was manufactured
  • Performing litigation testing on the proposed device, prove it does not work and debunk it.
  • Settling lawsuits when they must to avoid adverse rulings

We are not saying marine drive manufacturers are evil, they are just defending their position as all industries do. They are just doing their job.

All in all, the industry has been very effective in the court room over the years on propeller safety issues. If you read their defense above, it sounds pretty reasonable, until you recognize several propeller safety issues have become perpetual, claiming lives year after year, decade after decade.

We suggest it would be in the best interest of consumers if the boating industry more aggressively applied the basic 3 step Safety Hierarchy (Design, Guard, Warn) process to perpetual propeller accident scenarios vrs trying to defend against proposed solutions.

The Hierarchy of Controls

The Hierarchy of Controls is somewhat of an industrial / workplace version of the Safety Hierarchy. The steps are typically listed as:

  1. Elimination – physically remove the hazard
  2. Substitution – replace the hazard
  3. Engineering Controls – isolate people from the hazard
  4. Administrative Controls – change the way people work
  5. PPE – protect workers with Personal Protective Equipment
Hierarchy of Controls image courtesy of CDC

Hierarchy of Controls
image courtesy of CDC

Some groups see the Hierarchy of Controls laying over the Safety Hierarchy with elimination and substitution representing designing out the hazard, engineering controls representing guards and interlocks, Administrative control representing training and instruction, and Personal Protective Equipment being the same. Others suggest all these steps apply to industrial machinery after it has been delivered to the factory floor. Local safety professionals use these tools to make machinery used in their factories safer for their specific uses, employees, and environment.

At any rate, it is another way at looking of some of these issues, plus some people will think you are asking about the Hierarchy of Controls if you ask them about the Safety Hierarchy.

Haddon’s 10 Countermeasures

Haddon’s 10 Countermeasures, William Haddon Jr.’s ten steps to reduce losses from the quick release of pent up energy, is an excellent tool for use in conjunction with the Safety Hierarchy.

We previously wrote about Mr. Haddon’s work in our post, On The Escape of Tigers: Haddon & Bass Boat Propeller Safety.

Mercury / Kiekhaefer Corporation outboard ad featuring a tiger in 1955

Mercury / Kiekhaefer Corporation outboard ad featuring a tiger in 1955

The old Kiekhaefer / Mercury tiger ad above, was an effort to portray some of the “pent up energy” Haddon tries to control the release of.

A quick list of Haddon’s 10 Countermeasures is presented below. The source of the exact text of these steps and additional information on them is provided in the reference above.

  1. Prevent the marshaling of of the form of energy in the first place.
  2. Reduce the amount of energy marshalled.
  3. Prevent the release of this energy.
  4. Modify the rate of or spatial distribution of release of energy from its source.
  5. Separate in space or time the energy being released from the susceptible structure whether living or inanimate.
  6. Separate the energy being released and the susceptible structure whether living or non-living by a barrier.
  7. Appropriately modify the contact surface, sub surface or basic structure in eliminating, rounding and softening corners, edges, and points which can eventually come in contact with people.
  8. Strengthen the structure, living or non-living, that may be damages by the energy transfer.
  9. Move rapidly in the detection and evaluation of damage that has occurred or is occurring and counter its continuation and extension.
  10. All measures taken between the emergency period following the damaging energy exchange and the final stabilization of the process and long-term reparative and rehabilitative measures.

Haddon notes there is no order of priority to the strategies above. They can be applied in any order.


We suggest those considering the use of warnings as their first line of defense against propeller injuries review the list of steps required for a warning to be effective as listed below. Citation available at bottom of this page.

Also note, Mr. Haddon never specifically mentions their use in his list of 10 Countermeasures.

Sequence of Events for a Warning Sign or Label to be Effective

For a written warning to be effective, a sequence of events must happen. If any one of these steps is missing, the warning will not be effective and the person will be exposed to the hazard.

To be effective, a warning must:

  1. Be installed in a location that allows the remaining steps to occur before an injury occurs (those at risk need to have time to react)
  2. Remain present and readable (not fall off, not fade too much to read, not be painted over, not be damaged too much to read, etc.)
  3. Draw the attention of those at risk (they have to see it). If you are trying to warn people in the water when they are in the water, make sure the label is viewable from their position
  4. In addition to the steps above, for a written warning to be effective, those at risk must:

  5. Read the warning (most effective if by both word and powerful clear graphics to cross language barriers)
  6. Understand the warning AND the proper action to take if the situation presents itself (be sure the warning is in the language of the reader)
  7. Internally “buy in” (acknowledge this hazard could hurt them and decide they would like to avoid it)
  8. Maintain their desire to recognize the risk and to take the proper action should it occur
  9. Recognize the danger when it presents itself at a later time
  10. Recall the proper action to take
  11. Take the proper action in time to prevent the accident (change their behavior)

Upon review, most will recognize these ten steps (3 for the warning and 7 for those at risk) are not going to be successfully executed every time someone new boards or approaches a boat.
Warning signs are not THE answer to preventing propeller accidents. However, properly designed and placed warnings can be used in conjunction with other interventions to reduce the frequency and severity of propeller accidents.

Citation for the warning reference above:

1. Sequence of Events for a Warning Sign or Label to be Effective. Houseboat Propeller Injury Avoidance Measures Proposed and Withdrawn by the U.S. Coast Guard: an Analysis by the Propeller Guard Information Center. Gary Polson P.E.. Originally published June 10, 2010. June 15 2010 Version. Page 74.
Page # 135 of 374

Warnings Beyond Labels

When we think of warnings we typically think of warning labels like those seen in our coverage of the 2014 Tulsa Boat Show.

However there are many other types of warnings. Certain ones may be effective in some situations in protecting those on or near boats from safety hazards. For example, Mercury Marine’s Moving Propeller Alert uses a Signal Light (rotating LED light display) to alert those in the water at the stern the propeller is turning or the engine is in gear.

Willie Hammer does a nice job of listing possible warning methods in his book, Product Safety Management and Engineering. The second edition of that book has an extensive list of warning types with examples on pages 108-110.

Warning Types

  1. Visual Warnings
    • Illumination
    • Discrimination
    • Signal Lights
    • Flags and Streamers
    • Labels
    • Signs
    • Procedural Notes
  2. Auditory Warnings (sirens, buzzers, bells, alarms, voice communication, etc. – sometimes auditory warnings are used to draw attention to a visual display)
  3. Olfactory Warnings (smell)
  4. Tactile Warnings (vibration and temperature)
  5. Gustatory Warnings (taste)

Designers struggling to effectively warn of a hazard may find this section of Hammer’s book helpful.

Solutions Don’t Have to Be Perfect

We tend to be pretty hard on new product and new safety device ideas, quickly pointing out every minor flaw or possible shortcoming. But we need to remember many products that have been quite successful in the marketplace for decades don’t actually work very well.

For example few adult boaters in open motorboats wear life jackets, few boat operators attach their kill switch lanyard, many boat propeller warnings are far from optimized, etc. But the firms manufacturing life jackets kill switches, and warning labels, keep on selling them like hotcakes, and they do save peoples lives.

Plus don’t forget, propellers are the source of all these problems to start with, and they have been around a couple hundred years with annual sales in the millions of units.

A substantial improvement over existing approaches may not be perfect, but could still save a lot of lives.

Remember, the Answer is Not Always Devices

USCG Boat Responsibly Logo

USCG Boat Responsibly Logo

As the Coast Guard instructs, “Boat Responsibly”. Boaters obviously have a personal responsibility for their own safety and for the safety and those around them.

Some of the “non-device” tools mentioned earlier such as training, education, boat rental orientations, Public Service Announcements, regulations, and outreach programs, can play significant roles in addressing perpetual propeller accident scenarios as well, but it is our belief that design and engineering should play the lead role. These other methods and tools are sort of like warnings. A lot of things have to happen for them to be effective, while a design from which the hazard has been eliminated puts the problem to bed. Boats are typically used in a recreational environment. That is a long ways from the factory floor where manufacturers have great control over the actions of their workers and their training.


  1. As for attacking Perpetual Propeller Safety issues, we suggest beginning with the primary tools described in this posts (Safety Hierarchy, Haddon’s 10 Countermeasures, and Hammer’s expanded list of types of warnings). We also strongly suggest searching this website for previously provided solutions and technologies.
  2. As to the acceptance of these new or longstanding but not deployed ideas, we suggest OUTREACH methods being used and further developed by the Coast Guard AND Behavioral Economics techniques introduced at the March 2017 National Boating Safety Advisory Council (NBSAC) such as those in a book titled NUDGE by Thaler and Sunstein be used once the new approaches are properly vetted to deploy them with greater speed, whether than means deploying them to the boating industry OR deploying them directly to the consumer.
  3. Product Safety Management Guidelines. Second Edition. National Safety Council. Provides guidelines for product safety professionals.
  4. Product Safety Management and Engineering. Willie Hammer. Second Edition.
  5. ANSI B11 Safety of Machinery
  6. ABYC voluntary standards
  7. TRIZ, a structured problem solving method from Russia can be helpful in generating ideas when you hit a roadblock
  8. There are many tools in addition to those listed above, including: fault tree analysis, Failure Mode and Effects Analysis (FMEA), Haddon Matrix, Root Cause failure Analysis, Risk Assessment, Hazard Analysis, the bow-tie method, Human Factors Analysis, and Product Safety Reviews. However, as mentioned above, we suggest the methods featured in this post be tried first against Perpetual / Eternal boat propeller safety issues.
  9. And,

    Part 1 of this Post, Perpetual Propeller Accident Scenarios & How to Mitigate Them

As always, we welcome your comments.

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