BLOCK STACKING PRESENTATION

By Nina Potgieter


Block stacking is a storage method which uses no formal racking. The items to be stored are placed directly onto the floor surface of the building.

 

There are rules and regulations for block stacking to ensure a safe working environment. The Occupational Health and Safety Act, 1993, has a subsection "stacking of articles". Some of the items mentioned are:

  • The base level as well as articles in the stack must be able to sustain the weight exerted by the articles stacked above.
  • All pallets and containers need to be in good condition.

The question however is how high may I go?

The act states the following: "Provided further that where the containers (which refers to a unit such as a pallet with cartons or bulk bin) are of a regular shape and their nature and size are such that the stack will be stable, they may be stacked with the sides of the stack vertical if the total height of the stack does not exceed three times the smaller dimension of the underlying base of the stack." The act however continuous to say that "free standing stacks that are built with the aid of machinery (e.g. forklift truck) may, with the approval of an inspector, be built to a height and in a manner permitted by the nature of the containers being stacked".

I contacted the Department of Labour and questioned an inspector regarding this and he confirmed that the act is applicable to any container be it pallet, bulk bin, cartons, etc. Should an accident happen regarding stacked items and a written approval has not been given by an authorised inspector the persons in question(chief executive) will have some major legal problems.

 

The higher one can go the better the use of storage space, but the less accessible individual units become.

 



The major reason for not stacking very high is the stability of the stack and the problem of the bottom item bearing the load of the item on top of it. For a pallet with cartons the pallet on top may cause damage to the cartons below. To work around this problem, different equipment is available. One of these is stacking irons used in the fruit industry. These irons fit around the corners of the pallet like legs and are slightly higher in length than the bottom pallet stacked. The next pallet is placed on top of this base which then bears the weight and not the bottom pallet.




Other methods include the Cheprack and pallet cages. The Cheprack is assembled where needed and carries the weight of the pallets, etc. like a rack. The advantage is these racks are that they are not a permanent fixture and can be easily dismantled and stored out of the way when not needed. We have a representative from Chep here today if anyone wants to know more about these. During question time he can give more information.

 

All this type of equipment however has the disadvantage in that it needs to be assembled which uses manpower as well as time. But on the other hand you do not have the capital expense, permanence and rigid layout of a racking system.

It is however not just the height that plays a role in block stacking. The other aspect is accessibility and this is related to the number of aisles in the layout.

Aisles take up valuable storage space, but the more aisles, the easier it is to get to the pallet/bulk bin/ etc. A standard forklift truck needs at least a 4m aisle to be able to retrieve a pallet (1,2m x 1m) and turn. If we had a building of 15m x 27m and we stored pallets 10 deep as follows:

 

 

The more bays you have the better the accessibility because the row lengths are shorter, but then the longer and more aisle space is required. And as mentioned aisle space is expensive.

Our office did an interesting exercise for one of our clients regarding just this aspect of row lengths and utilisation of storage space.

We were investigating the effect on space utilisation if we needed to store one week’s fruit production in bulk bins stacked 10 high and each fruit cultivar and farm separately.

 

A Typical weekly delivery is as follows:

The size of a "delivery" to be stored separately therefore varies from a minimum of 35 bins to a maximum of 810 bins.

The question is, if bins are stored 10 high, how long should rows be to optimise building utilisation?

To accommodate the expected weekly production of 5721 bulk bins you have different combinations of row length and associated number of aisles. For this exercise we will quickly look at the effect of rows of 15 deep or 5 deep all 10 high.

If looking at only a few weeks delivery and one or two stores, it is quite easy to do this calculation for a range of row depths but if a large number of options have to be evaluated it will be better to draw up a linear programming model and to optimise the row depth/number of aisles.

 

One major advantage of block stacking is the fact that it dos not have any fixed racks restrict the layout. Therefore it is quite feasible to change the warehouse layout to accommodate the specific circumstances existing at that time.

One can easily make "sub-aisles" etc. which can be "there today, gone tomorrow".

You don’t have anything in your way, just one big open floor.

It will be necessary to ensure that location identification can accommodate such a changing warehouse layout and one way to do this is to divide up the entire warehouse floor into pallet spaces and to use the pallet module (say 1.15m x 1.5m) as the unit for all spaces i.e. aisles, pallet make-up, storage, etc.

For example only:

A building accommodating 80 x 40 pallet spaces.

 

No ridgid racking and flexible aisles

 

 

 



Click to go back to the Racking Seminar Page Click to go back to the Home Page