Forklift safety by design  

     <Resume>

by Barrett C. Miller

One percent of factory accidents involve forklift trucks, but the forklift accidents produce ten percent of the physical injuries.(1) Forklift accidents are usually blamed on operator errors. After each accident, we hold a training session for the driver. However, as many as 25 percent of these accidents are caused not by the driver but by controllable environmental factors. We can eliminate hazards and design a safe operating environment only when we understand the real cause of forklift incidents.

Ten lift truck accidents previously blamed on operator error were investigated as part of a safety curriculum project. The project attempted to determine the adequacy of standard forklift training courses. Each accident was serious and had produced an injury. The environmental design aspects found in these accidents are discussed here.

The Black accident
John Black worked in a factory where he made coffee cans. He worked at the same factory for eight years and knew the plant routine. On Friday morning, on his way to the storeroom, he stopped to talk to the woman who ran the palatizer.

Suddenly, a forklift truck struck him from behind. The collision broke Black's hip. An insurance investigation determined that the forklift driver was not watching where he was going. The report criticized Black for not paying attention.

There was a history of forklift accidents in the canning plant - each reportedly caused by operator error. The second investigation showed other contributing causes:

1. The warehouse was dark. Light readings measured 5 candlepower - far under the acceptable level for general operations.
2. The plant was noisy. The sound level measured 100 decibels. OSHA Inspectors cited the company for noise violations twice. Sixty percent of the employees suffered hearing loss. John Black suffered a loss of 30 percent of his hearing capacity during eight years of employment.
3. No pedestrian routes or protective islands existed.
4. Vehicles traveled through the factory too fast. A radar gun measured the average speed through the area where the accident occurred. The average truck passed the accident location at eight miles per hour. Production line speed pushed forklift speed.
5. The forklift did not have an automatic back alarm.

Measurements were made to establish the operator's point of first possible reaction and the stopping distance of the vehicle. Computations showed that the operator could not have responded in time to prevent the accident. An automatic backup alarm was essential.

Speed Limits
Regulating the speed limit of an industrial truck is an important part of the environmental design of the workplace. A forklift truck moving through a warehouse had tremendous momentum. Momentum is the mass of an object multiplied by its velocity. Mathematically, momentum is Weight x Speed x 1.5. 

A 5,000-pound forklift moving through a warehouse at ten miles per hour with a 4,000-pound load has a potential destructive force of 135,000-foot pounds of energy. A loaded forklift travels through a warehouse with the force of a Cadillac Eldorado driving 20 mph.

A lift truck cannot stop in an instant. G. E. Lovested(10) showed that it takes about 1.3 feet for each mile per hour for a panic stop. It takes 0.75 second for the operator to become aware of the existence of a hazard and another full second for the mechanical parts of the vehicle to respond.(2)

A forklift truck moving at ten miles per hour may take 40 feet to stop.* Theoretically, the operator should allow 40 feet between the truck and a person on foot. Since this is not practical, we reduce forklift speeds and establish operating rules.

Lovested says that the maximum speed limit allowable by a forklift truck is eight miles per hour. In areas where pedestrians are present, speed limits should not exceed three miles per hour. Radar measurements of forklift speeds in factories show Lovested's suggested speeds are appropriate. All speed limits and other traffic advisories should be posted.

The Lighting
As we reach age forty, our eyes go through predictable changes. The lens becomes progressively opaque and the muscles which control the focus of the lens weaken. The condition continues to degenerate until about age sixty when our eyes reach a more or less permanent state of vision. The change is gradual. We seldom recognize the loss of sensitivity.

It requires six times as much light for a man sixty years old to discriminate objects in dim light as it takes for a twenty-year-old man.(3) The effect on the worker is predictable. As we lose our ability to discriminate objects in dim settings, we become more sensitive to glare. A forklift driver may have too little depth perception in a dark warehouse. He may not see a fellow employee in time to respond.

We measure light in footcandle units and in lumens per square foot. We use a high-quality color-corrected photographic light meter for measurements. OSHA established a minimum standard for lighting in areas where forklifts operate. (4) If the light level in an area is below 2 lumens per square foot, the truck must use auxiliary lights.

Forklift trucks normally carry their load in reverse, making auxiliary lighting a complex task. Two lumens per square foot equals 2 footcandles. The light in a warehouse measuring 2 candlepower is seriously substandard. All safety codes recommend a minimum light level of 20 footcandles in warehouses.(5) This level of illumination should be adequate for older workers.

Warning Devices
All forklift trucks must have a horn. The driver must monitor the direction of travel and use the horn to warn pedestrians who may be in his blind spots. A blind spot is by definition any place in the direction of travel which the driver cannot see without special effort.

The property use of the horn is an important part of the facility design. Some employers require the driver to honk as he begins to move; others isolate pedestrian hazard points at which to use the horn.

It is important to discover all environmental blind spots in the driver's path and evaluate the risk of each. A walk-through of the area reconstructing the field of view of the driver is necessary. You can then follow these simple steps.

1. When approaching an aisle, determine at what point the driver can first see an approaching pedestrian.
2. Next, determine the point at which he is likely to see the pedestrian.
3. Compute the desired speed in the area in feet per second. Multiply the measured speed by 1.5 (You may use 3 mph as a standard speed limit.)
4. Multiply the speed, measured in feet per second, by 1.75. This will provide a measure of the mechanical delay of the driver and the vehicle.
5. Add 1.3 feet for each mile per hour of your established speed limit.

If the speed, plus the mechanical reaction delay, plus braking distance is less than the point of the first likely perception, you do not have a blind spot. If the computed stopping distance is longer than the point of first likely perception, a workplace design modification is necessary. You may lower the speed limit, or require the driver to honk as he approaches the intersection.

Employers should not rely exclusively on the horn as a warning device. The nature of a forklift requires the driver to divide his attention. He carries his load while driving in reverse. He must simultaneously monitor the balance of his load at the back of the truck and watch the direction of travel. He drives with his left hand on the steering wheel and his right hand on the load control. He must monitor his blind spots. When he uses the horn, he automatically gives up some control.

The complexity of a driver's tasks makes the use of an automatic backup alarm system mandatory.(6) The choice is not whether to use an automatic alarm, but which alarm to use. Factory representatives normally advise the user which alarm to install. If the facility is noisy, a flashing light may be best, otherwise an audible horn is adequate.

The Harris accident(7)
Any drove a forklift at a South Florida tamale factory. One routine job involved unloading and storing cardboard containers delivered by truck from another state. Each bale of cardboard weighed 700 pounds and the bales were stacked double. As Andy attempted to take a stack off a truck, the top bail slid off and into Don Harris, the truck driver. The accident hurt Harris seriously.

In the civil suit which followed, Andy testified that he had no driver's license. The courts had suspended his license twice for drunk driving. He had no forklift training. A previous employer offered to send him to a forklift program. He refused to attend because the employer required him to pay for his own training.

Andy stated that he had not tipped the load to stabilize it before beginning to move. He claimed there was not room at the top of the truck. Andy admitted that he had previously dropped loads off his forklift and blamed the accidents on the driving surface. He said that he handling of the forklift truck was very unstable. He used his stands to describe the motion of the truck - it floated. An accident investigator determined that Andy was at fault and the employer fired him.

An employer should not trust the operation of a forklift to an employee with a bad driving record. A National Safety Council report recommends that an employer check driving records annually. It recommends an annual physical examination.(8) No operation should drive a forklift without training. There was no excuse, however, for the investigator to fail to check Andy's story.

The second investigation found a number of contributing causes:

1. The surface of the parking lot was defective. It was so bad that it was a clear violation of OSHA regulations. A thin layer of asphalt laid on a bed of sand served as a working surface.
2. The top bale sat four inches from the top of the truck. There was no room to top the load back before moving. There was no way to remove the load safely with a forklift.
3. The owners carelessly altered the ballast of the truck with the wrong replacement parts. The forklift battery was 600 pounds too light for the vehicle.
4. The forklift had solid tires. Solid tire forklift trucks are for use on smooth concrete floors.

The design of the job was unsafe.

The Working Surface
A forklift truck must operate on a smooth level surface. It is not possible to conceive of a working surface more inadequate than the one in the Harris accident. A thin layer of asphalt lay on a sand base. On a hot August afternoon, the 9,000-pound load sank into the surface leaving voids.

Tires
Many forklift trucks use hard rubber tires designed for concrete surfaces. Hard tire forklifts are inside trucks. They have no suspension, and the solid tires have no air cushion to absorb the shock from a defect in the working surface. if used on a rough surface, a hard tire truck will handle erratically.

If you use a solid tire forklift outside, the surface must be perfect and capable of supporting the load. If you use the forklift truck outside regularly, use a pneumatic tire forklift. the pneumatic tire spreads the load over a larger surface footprint and helps absorb the shock.

Forklift Ballast
Forklift trucks are like seesaws. The vehicle is safe when both ends of the seesaw are in balance. If the load is too heavy or if the ballast is too small the forklift truck will tip toward the heavy side. The seesaw analogy works to a point, but it is too simple.

Both steering and lateral stability are affected by the ballast of the truck. Any change in the ballast will alter vehicle stability in four directions and will make steering unpredictable. Sometimes the change in ballast causes the vehicle to understeer.

In other situations, a change in ballast will cause it to oversteer. Thus OSHA regulations forbid the alteration of the ballast and require the use of exact replacement parts.(9) All modifications require the written approval of the manufacturer.

Many modifications to the ballast are unintentional. The installation of a taller or heavier mast, for example, alters the balance of the forklift. Some operators add ballast to the back of the truck to increase its lifting capacity. This practice is always dangerous.

Users of electric forklifts face a specific temptation. They sometimes use lighter replacement batteries because they are cheap. Electric batteries often weight several thousand pounds and cost thousands of dollars. By installing a smaller battery, the user can save hundreds of dollars.

Operators often know that they are reducing the lifting capacity of the truck, but do not understand the danger. Their misunderstanding is often reinforced by battery dealers anxious to make a sale. A prudent buyer will get all dealer representations about replacement batteries in writing.

Other accident patterns
A number of other accidents demonstrated environmental and design defects.

Aisle Width
Tim worked in a meat packing plant. He stacked 600-pound boxes of beef on shelves in the freezer. Tim lost a finger when he caught it between the forklift truck and a metal shelf. This is the eighth most common forklift accident.

Two contributing causes were found. First, there was insufficient space between the forklift and the side of the shelves. There were no more than four inches on each side for maneuverability. Second, the floor of the freezer was very icy. A design defect in the cooling system caused the floor to ice up. If the load was uneven when placed on the shelf, the forklift would slide to the side.

Traffic Control Signs
Eric drove off the dock of a school board warehouse. An inspection of the dock showed that it is very narrow. In addition, the edge of the dock was difficult to see. Forklifts were not required to stop before entering the dock area.

As the driver approached the ramp in the later afternoon, he faced the sun. His eyes had not time to adjust from the relatively dark warehouse to the relatively bright dock. A stop sign at the entry to the ramp will give the driver's eyes time to adjust to the intense light. Painting the edge of the dock with high visibility yellow will help the driver's depth perception. Two environmental modifications may prevent future accidents.

Pedestrian Islands
A number of pedestrians were hit by forklifts when they appeared suddenly in unexpected places. We carefully segregate automobiles and pedestrians in parking lots, but we forget to mark traffic patterns in the warehouses.

Any area where pedestrians and vehicles interact needs markings to show traffic patterns for pedestrians and vehicles. If a warehouse is large enough, mark stock storage areas, traffic areas, and pedestrian routes on the floor.

Summary
Ten forklift truck accidents were investigated as part of a curriculum development project. Each was selected randomly from serious accidents previously blamed on driver error. The accidents represented a broad range of accident types. In some the forklift had driven into a pedestrian. In others, the forklift dropped its load on a pedestrian. Usually, a number of contributing causes were discovered. The study showed that many accidents are preventable by controlling facility design. Facility design caused three of the ten accidents investigated.

Safety literature shows that the two leading causes of forklift accidents are (1) workers struck by the forklift, and (2) having the load dropped or shoved onto another employee. Other causes include the driver catching part of his body between the truck and other objects, or driving off the loading dock.(10) This investigation concluded that patterns of forklift accidents remained unchanged. Most accident causes are discussed in existing forklift training courses, but little guidance exists to train employers about environmental design.

OSHA requires the development of safe operating rules.(11) An employer can provide a safe environment by following simple steps. Post speed limits. Calculate and lay out the facility based upon vehicle and pedestrian movement patterns. Provide pedestrian zones to isolate the hazard. Install mirrors to give the forklift driver additional time to react. The operating surface must be smooth and unobstructed and the forklift must be selected for its expected use.

*Stopping Distance = Reaction Distance - Mechanical Delay - Physical Braking Distance.

References
1. Laney, James, "How to Make Forklift Truck Safety Uplifting," National Safety News, National Safety Council, Chicago, IL July 1984.
2. Rivers, R. W., Traffic Accident Investigators Handbook, Chas. Thomas Publ., Springfield, IL, 1979.
3. IES Handbook, 5th Ed., Illuminating Engineers Society, New York, 1972.
4. 29 CFR 1910.178(h)
5. Practice for Industrial Lighting, American National Standards Institute, A132.1, Washington, D.C., 1973.
6. Accident Prevention Manual for Industrial Operations, National Safety Council, Chicago, 8th Ed., 1980.
7. Harris v. Catalina Finer Meat Corp. 86-10504, 13th Judicial Circuit, Tampa, FL.
8. "Powered Industrial Life Trucks," National Safety News, Sept. 1977.
9. 29 CFR 1910-178(q)(6).
10. Lovested, Gary, "Top Ten Forklift Truck Accidents," National Safety News, Sept. 1977.
11. 29 CFR 1910.178(n).