High-density mobile storage systems are used widely as the most space-effective method for information and materials storage. However, space efficiency alone should not be the deciding factor in designing the right mobile storage system. Protection -- of stored materials, operators and the systems themselves -- also must be considered.

Increasingly, mobile storage is being used beyond areas where access is limited to trained personnel, to places where the general public will use the systems -- where protection becomes more of an issue.

Mobile storage systems are important components of a company's operation. They must be used widely and protected from abuse by careless operators. The systems operate so smoothly that an operator moving a carriage by hand may not realize that he or she can be moving tons of material with significant momentum -- especially with hand-cranked systems. This can seriously affect a person or object in a closing aisle if the movement is not properly controlled.

Stored materials themselves are becoming more diverse. Mobile systems store not just files and books, but also fragile and irreplaceable items that must be secured and protected. The systems have evolved from carriages that are simply pushed apart by hand to create an aisle, to units with sophisticated electronics that can provide a variety of protection and security options.

However, despite the expanded use and sophistication of mobile storage, many systems are still designed with one thought in mind: how to store the most stuff in the least space for the least cost. But obsession with initial cost should not blind us to lifetime economies and to the need for protection. Ignoring protection can have a high price tag.

CONSIDERATIONS FOR HIGH-DENSITY MOBILE STORAGE

• Space available
• Architectural obstructions
• Floor-load rating
• Seismic codes
• ADA guidelines

Materials/information Stored

• Shape, size, weight of stored items
• Current and projected storage needs
• Type of material stored (delicate, valuable, refrigerated, temperature/humidity controlled, off-gassing, etc.)

Operation/protection

• Level of training, understanding and ability of least-trained, least-able operator
• Level of access required (secured, locked, open, etc.)
• Frequency of access (how often, by how many people at one time)
• Work and traffic patterns
• Length and number of carriages
• Type of material stored (heavy, delicate, irreplaceable, etc.)
• Control mechanism (manual, mechanical assist, electric)
• Organization's safety policies
• ADA compliance
• Fire protection/security

One example is a mobile system in an office file room that is not meant for the public access. Theoretically, the system will be used only by trained employees. A manual or mechanical-assist (hand crank) system would seem to be the most cost-effective choice. But what about on Saturdays, when parents may bring their children into the workplace while they catch up on paperwork? What child wouldn't want to try out the system? And what if new or temporary employees are not properly trained? The more prudent choice might well be an electric system.

This is not to say manual or mechanical-assist systems are unsafe. In the right setting, each is perfectly safe. But except for very small systems with short carriages, they don't belong in public access places. That's why most public libraries, for example, use electric systems. A closer look at the operations of manual, mechanical assist and electric systems will make the reasons clearer.

System Types, Protection Options
Manual mobile carriages are simply pushed apart by hand. The sheer force required to move a carriage limits its length to eight to 10 feet. Most of these systems are small -- two to four carriages -- and accessed regularly by one or two people. At this length, with a limited number of operators, it is easy to peek into an open aisle to make sure it's clear before moving a carriage. Even if a carriage begins to move with someone in an open aisle, that person probably can stop the movement by hand.

Longer carriages, when fully loaded, become too heavy for the average person to move by hand. A mechanical assist or hand-crank device uses a leverage system of chains and gears that can move carriages weighing thousands of pounds with one hand. Large systems have numerous carriages and are accessed by a number of people, sometimes simultaneously. Each person may not stop to look down an aisle before closing it, and someone may get caught in the aisle who does not have the physical strength to stop a carriage or the presence of mind to call out for help.

Therefore, at least rudimentary safety devices should be provided to protect operators. Options might include a locking pin that is set and released by hand to control the movement of a carriage. An automatic aisle lock will automatically lock an aisle open until the control is released by hand.

Electric mobile storage systems, by virtue of their electronic controls, offer a higher degree of sensitivity and passivity in protecting people and objects. One group of options is semi-passive, requiring conscious manual effort or physical or photoelectric contact with a person or object in an aisle. A second group of devices is passive, requiring no conscious manual effort or physical contact other than standing in an aisle.

A third type of protection device will monitor persons entering and leaving open aisles and prevent carriage movement when anyone or anything is in the aisle, whether or not they are actually standing on the floor. Monitoring systems require no conscious action, physical contact or weight activation.

One semi-passive option is a mechanical sweep consisting of a mechanical switch plate on the base of a carriage. When the plate comes into contact with a person or object, it stops carriage movement. Another level of protection is provided with the addition of an aisle entry sensor, which prevents carriage movement when a cross-aisle infrared beam is broken. Both must be reset by hand to resume operation of the system.

A more sophisticated device is the safety floor, which is activated by a person's weight and locks an aisle open. A mechanical sweep can be replaced by a photo-electric sweep that stops carriage movement when a beam of light is interrupted by an object or person.

Combining the photosweep with a direction-sensing photoelectric quadrature systems and a system of photoelectric cross-aisle sensors linked by a computer logic system creates a monitoring system.

Electric systems also offer nearly unlimited options in length, weight and number of carriages. They can be accessed simultaneously by a number of people. A benefit of this kind of system is that a person can enter an aisle as soon as there is enough room rather than having to wait until the aisle is completely open. The protected aisle will continue opening as one or more persons enter and prevent the aisle from closing until all persons leave the aisle. Safety floor systems, however, stop as soon as a person steps on the floor.

Electric mobile storage systems also are the easiest to operate for people with physical disabilities. A carriage is moved at the simple touch of a button on the face panel or on a remote control device. Options like automatic aisle lighting can speed access and lessen the need to hunt for a light switch.

Clearly, the abilities and level of understanding of the least trained, least able person with access to the system must be a prime consideration in the design and installation of a mobile system.

Protecting Materials and Information
Anything worth saving is worth protecting. Because mobile systems are mobile, the effect of the movement on stored materials is an important consideration.

When operated by trained and/or conscientious people, a moving carriage in a manual or mechanical assist system should barely bump the adjoining unit. However, it is possible for units to be moved carelessly and with a force great enough to bang carriages together and shake up their contents.

This may be a primary concern when contents are fragile and/or valuable, such as museum artifacts, pharmacy bottles or laboratory slides. The bellwether system for protecting contents is the National Archives at College Park, MD, commonly known as Archives II. It is the world's largest archives building, constructed around the world's largest high-density mobile storage system which protects thousands of records, including priceless, irreplaceable manuscripts, photographs, maps and drawings that are an important part of our nation's heritage.

The U.S. National Archives and Records Administration specified an electric system because it offers easier operation, faster access, greater flexibility and a wider range of state-of-the-art safety, fire protection and security features than mechanical or manual systems.

The movement of electric carriages is automatically controlled, with a soft start and stop. This protects contents against jostling. In addition, the computor logic available on electric systems can be tied into building fire and security systems.

As part of a state-of-the-art fire protection system, the Archives II mobile system features a special "fire park" mode controlled by the building's fire mangement system that automatically creates flue spaces between the carriages so sprinkler water flows more efficiently and flames cannot "jump" across aisles. The building has quick-response sprinklers and ionization-type smoke detectors to set off the alarm and sprinklers before flames or smoke become visible.

The computer logic available on electric systems can be programmed to restrict access to a system, closing it until the proper code is entered or identification card presented. It can then track who accessed what aisle, when and for how long. It can even be tied to computer tracking systems to automatically open the right aisle for a specific file. Different departments can be restricted to certain aisles.

In Archives II, the mobile system's electric controls are tied into the building management control system, and storage modules in restricted areas require security cards and access codes to prevent unauthorized use.

As discussed earlier, photoelectric safety devices available on electric systems offer the best protection and least potential for damage to an object moving in an aisle. A moving carriage does not have to come into contact with the object in order to be stopped.

Protecting the Systems
Most high-density mobile storage systems are built to last for decades of use. However, the best protected systems are those whose movement is controlled, either by trained operators or electronic controls.

Security often goes hand in hand with protecting the systems from abuse. Correctional institutions, for example, often have a "triple lock" system that requires three keys for access -- to a locked mobile system in a locked room in a locked area. A person going through that much security probably will treat the system with care.

Similarly, mobile systems can be designed so that individual aisles and/or the whole system can be locked mechanically (with a key or bar, for example) or electronically (with a code or card swipe for access). Also, systems can be equipped with an anti-tip device that will help carriages stand up to earthquakes or a prankster climbing on the shelves.

Selecting an Appropriate Mobile System
Protection -- of operators, materials and systems -- is just one of the factors to consider when designing a mobile storage system. Other considerations include the amount and shape of the space and the type of materials to be stored, the degree of access required and how the system will fit into the floor plan and work patterns of the facility (see sidebar).

A system that is appropriate in one context may not be in another context -- even within the same department. When the context of a system changes -- the level of training, frequency of access, materials stored, location, etc. -- the mobile system should be re-evaluated to make sure the method of operation and level of protection are still appropriate.

Such evaluation is often best done by a trained mobile storage designer and installer. These professionals are experienced in addressing all the considerations, and can offer site visits to installations facing similar challenges. These evaluations and design recommendations are normally free as part of a professional consultation.

As more and more organizations discover that high-density mobile storage is the answer to their information and material storage needs, considerations in protection become imperative.