Work Safety in Very Narrow Aisle Warehouses

By Thomas Da Ronch
Director, ELOKON

Introduction

For many years the search for high storage density, fast stock storage and removal, and low pallet storage costs has quickly led to the need for narrow aisle warehouses.

A narrow aisle warehouse is characterized by the fact that:

• It is a racking facility
• It has lanes (termed very narrow aisle) between the racking rows, which are scarcely wider than the manned “very narrow aisle trucks” which operate in them.

These very narrow aisle (VNA) trucks are just a few decimeters narrower than the distance between the two racks. For many companies this type of storage offers the ideal solution for achieving their own high logistics goals. However, due to the narrow width of the aisle, accidents can occur. The attention of the VNA vehicle driver is often focused on the racks above and not on what is in front or behind the VNA vehicle.

In 1989, the first mobile safety system was placed on the market (based on passive infrared technology) to help address potential dangers. The same year, a framework for the safety and health of workers at work was put into place in Europe: EU-directive 89/391/EEC, which states 'employers have the general duty to ensure the health and safety of their employees'. In addition, the machinery directive, EU-directive 89/392/EEC, was developed which states 'machinery may be placed on the market and put into service only if they do not endanger the health or safety of persons'.

These EU directives help set the stage for the European machinery directive to become mandatory in 1995. As a result, many European very narrow aisle truck manufacturers incorporate the Aisle Alert System™, a non-contact, safety-rated solution from SICK and ELOKON, as part of their standard safety offering. There is no mandatory requirement, however, in the U.S.

Work safety and productivity go hand in hand

What happens when a company wants to improve obligations regarding work safety in its VNA warehouse? How can it achieve its productivity goals and create a safe workplace? Which dangers, which precautions, which measures must be taken into account to guarantee staff safety?

Finding the correct answer to these questions is all the more important when it is recognized that the correct interpretation of safety not only results in greater safety but also that turnover and productivity in the VNA warehouse can be optimized.  

In the forward part of a VNA warehouse there is usually an area (apron) for free-moving goods, persons and/or VNA truck traffic. Goods are brought to and transported from the very narrow aisle area via this apron. It is normally also used by the VNA trucks to change aisles.

The apron is therefore heavily used by foot traffic, forklifts and goods traffic.

Dangers arising in the VNA warehouse can be categorized into two groups:

1. Dangers in areas where very narrow aisles meet other routes (apron, escape routes and other cross-routes): contingent on the movement of VNA trucks in very narrow aisles (speeds of up to 12 km/h (7.5 mph) are possible), and the crossing of persons or other VNA trucks, accidents can happen.
2. Dangers within the very narrow aisles: an approaching VNA truck can strike persons who enter the very narrow aisle (e.g. for load picking). Collisions between several VNA trucks operating in the same very narrow aisle are also possible.

The operator must determine the specific dangers of the warehouse, then assess them with a risk analysis and finally select suitable measures to guarantee safety.

Precautions

Possible measures to avoid risks for persons within very narrow aisles are:

A. Operating instructions/training: Rules for warehouse operation must be drafted in writing. These should regulate safety measures and the behavior of employees and list reduced as well as residual risks. It must also be ensured that employees are trained at suitable intervals both before and after starting employment.

B. Traffic management : traffic rules must be set down for VNA trucks and pedestrians (e.g. right of way, direction of travel, authorized or closed areas). The following possibilities are conceivable:

• Rack operation by forklifts only: it must be established that only VNA trucks are permitted in the very narrow aisles.
• Rack operation by pickers only: it must be established that only pedestrians are permitted in a particular warehouse area (therefore not a very narrow aisle area).
• Non-simultaneous rack operation : it must be established that no pedestrians are allowed in a very narrow aisle at the same time as a forklift.
• Simultaneous rack operation : it must be established that trained and specially authorized staff is also permitted on foot in the aisle at the same time as a forklift.

C. Safety labeling: suitable safety signs must be affixed to the entrances to the very narrow aisles.

D. Speed limited to 4km/h : if all the criteria listed below are fulfilled, the risk of collision between VNA trucks and persons can be regarded as sufficiently minimized by limiting the forklift speed to 4km/h:

• The VNA trucks cannot remove and insert complete load units and are only designed for picking by hand;
• The operator cannot be lifted more than 1.2m;
• There is an unobstructed view of the aisle in the direction of travel in every operator seat position;
• Only forklifts are permitted in the aisle;
• The forklift has an optical warning system, which is automatically switched on in the very narrow aisle.

E. Speed limited to 2.5km/h: if all the criteria described above (see point D) are fulfilled apart from the presence of an optical warning system, sufficient safety can be ensured by limiting the speed to 2.5km/h.

F. Aisle end safety mechanism: before leaving the narrow aisle as well as before crossing intersections (exception: escape routes for operating staff) the VNA truck speed must automatically be reduced to a maximum of 2.5km/h. The risk is thus minimized when crossing the apron.

G. Collision safeguard: if several VNA trucks are to be operated in the same aisle an automatic device must be fitted to counteract the risk of a collision between VNA trucks.

H. Aisle type: aisles for VNA trucks and for pedestrians must be separated by their design (e.g. VNA truck aisle is wider than the pedestrian aisle): this prevents the VNA truck from entering the pedestrian aisle. The risk for persons in these aisles is then minimized (not however the risk that persons will walk into the (VNA truck) aisle).

I. Building measures: the aisles in which the VNA trucks operate are secured against access by unauthorized persons, by fences, doors, conveyors, transfer points. This also prevents persons from being injured.

J. Mechanical barrier: entrances to the narrow aisles are fitted with mechanical barriers, which automatically prevent pedestrians and forklifts from being in a very narrow aisle simultaneously. The risk for the pedestrian is thus minimized.

K. SICK Aisle Alert System: < a non-contact, automatic protection system fitted to the VNA truck which uses laser technology to monitor the operating range of the VNA truck in the aisle and automatically slows the forklift, or stops it completely when it detects persons . This system has a wider sensing field than traditional non-safety solutions, providing earlier detection of objects. The system actively helps prevent injuries to pedestrians.

L. Warning system: light grids are fitted in front of the entrances to narrow aisles which ensure that persons and pedestrians are not present in one and the same aisle. If the rule is infringed (e.g. a forklift enters an aisle in which there are pedestrians) an opto-acoustic alarm is triggered. The risk for pedestrians is thus minimized.

The right mix of measures is the most important thing

The aforementioned criteria must be selected individually for the warehouse (existing risks, equipment types, desired working methods, etc.). While measures A, B and C are implemented everywhere, the others are selected as required (i.e. when a corresponding risk exists; e.g. if 2 forklifts are supposed to enter an aisle, collision protection must be provided) and/or as desired (if a risk must be minimized it can be minimized by one or another equally effective measure). Here the mix of measures is always important as only a coordinated package of measures can guarantee that the risk is minimized and productivity and flexibility in the warehouse can be maintained or even increased.

Typical configurations

In practice several typical warehouse configurations have emerged which correspond to typical safety measures. Listed below are the most common situations.

Case A) Narrow aisle warehouse without pedestrian access

Description: with this configuration only VNA trucks are allowed in the very narrow aisles. Pedestrians are not allowed. There are no additional aisles for pedestrians.

Risk for pedestrians: although pedestrians are not permitted in the aisles they often work on the apron and can walk into a very narrow aisle unhindered (although this is not allowed).

Risk assessment: the risk that a pedestrian will walk into a very narrow aisle without a corresponding precaution to prevent it is then characterized by:

• Probability of occurrence: if the warehouse is designed with VNA tuck-only aisles, the risk probability is low because a pedestrian will seldom actually enter a very narrow aisle and/or only for a short time (it must be assumed that this situation will occur in spite of the sanction. A chain across the rack – as is often fitted – does not help to prevent this)
• Severeness of the consequences of an accident: if a VNA truck hits a pedestrian, this can certainly lead to serious injuries including death.
• Possibility of averting danger: the pedestrian cannot evade the danger in the aisle because the forklift’s speed, the pedestrian is usually occupied with picking (he therefore does not notice the forklift’s movements) and there is no room to dodge out of the way.

The operator cannot avert danger as his sight is restricted and is concentrating on removing or inserting goods.

Although we are speaking of a very narrow aisle warehouse in which pedestrians are not permitted there is a relevant risk which must be minimized.

Measure package: In practice the solution consisting of basic safeguards A, B and C and technical solution K or alternatively L has proven itself. With that not only is safety ensured but also more flexible use of the warehouse in the future is not excluded (e.g. non-simultaneous operation by forklift and pedestrian is not excluded).

Tip: from a purely economical standpoint, depending on the number of forklifts and aisles, either the Aisle Alert System (not so many aisles per forklift) or the warning system (lots of aisles, few very VNA trucks) is the more practical solution. Purely from the point of view of flexibility for the operator, however, the advantages of the non-contact, safety-rated Aisle Alert System are greater.

Case B) very narrow aisle warehouse with non-simultaneous pedestrian access

Description: With this configuration either VNA trucks or pedestrians may be present in the very narrow aisle. Operation is non-simultaneous: either a VNA truck or persons is in an aisle. The simultaneous presence of pedestrians and forklifts in the same aisle is thus impossible.

Risk for pedestrians: although pedestrians and forklifts may not be in the same aisle simultaneously this situation can occur deliberately or accidentally.

Risk assessment: the risk that a pedestrian will enter the very narrow aisle if a corresponding precaution does not prevent it is then characterized by:

• Probability of occurrence: with this type of warehouse operation the probability of occurrence is low because a pedestrian will rarely and/or briefly enter a very narrow aisle where there is also a VNA truck (despite the restriction it must be assumed that this situation will occur! A chain across the rack – as is often fitted – does not help to prevent this).
• Seriousness of the consequences of an accident: if a VNA truck strikes the person this can certainly lead to serious injuries including death.
• Possibility of averting danger: the pedestrian can hardly evade the risk in the aisle because the forklift moves quickly, the pedestrian is usually preoccupied with picking and therefore does not follow the forklift’s movements. There is no room to move out of the way. The operator cannot easily avert danger as his sight is restricted and is concentrating on removing/inserting goods.

Although pedestrians and forklifts may not be in the same aisle together a relevant risk still exists which must be minimized.

It should hereby be noted that the risk is not higher as in the previous “Case A,” although flexibility due to warehouse operation with pedestrians is higher

Measure package: In practice the solution consisting of basic measures A, B and C and technical solution K or alternatively L has proven itself.

Tip: from a purely economical standpoint, depending on the number of forklifts and aisles, either the Aisle Alert System (not so many aisles per forklift) or the warning system (lots of aisles, few very VNA trucks) is the more practical solution. Purely from the point of view of flexibility for the operator, however, the advantages of an Aisle Alert System are greater.

Case C) VNA warehouse with simultaneous operation by pedestrians and VNA trucks

Description: with this warehouse configuration VNA trucks and pedestrians may officially be in the same VNA aisle simultaneously.

Risk for pedestrians: there is high risk with this configuration. Pedestrians and forklifts are working directly next to each other in the same aisle!

Risk assessment: the risk is characterized here by:

• Probability of occurrence: with this type of warehouse organization the probability is high because a pedestrian will actually enter the VNA aisle where there is a VNA truck constantly and/or for a long time.
• Seriousness of the consequences of an accident: if a VNA truck strikes a person this can certainly lead to serious injuries including death.
• Possibility of averting danger: the pedestrian can hardly evade the risk in the aisle because the forklift moves quickly, the pedestrian is usually preoccupied with picking and therefore does not follow the forklift’s movements. There is no room to move out of the way. The operator cannot easily avert danger as his sight is restricted and is concentrating on removing/inserting goods.
• The risk is therefore very high and must be effectively minimized.

Measure package: In practice only the solution consisting of basic measures A, B and C and technical solution K has been proven to provide sufficient risk minimization for this kind of use.

Certain additional constructive and functional sub-safeguards must be considered so that the effectiveness of the Aisle Alert System is ensured (e.g. the rack must not have any openings in which pedestrians can hide; the Aisle Alert System must not demonstrate any automatic bridging functions within the VNA aisle).

Tip: Before this type of warehouse organization is chosen, expert advice should be sought. The structural and functional sub-requirements are limiting, making it necessary to check the advantages and benefits for each individual application case.

Summary:

Through the right choice of precautions, investment in sufficient safety can increase productivity figures in the warehouse and become a financial advantage for the company. Without involving complex technical and structural solutions, the Aisle Alert System in particular can also be easily retrofitted when buying new forklifts.

To order back issues of this publication, call 518.329.0067 or
visit our back issues page.