Three years ago Design News reported on a mobile surgical facility, the Advanced Surgical Suite for Trauma Casualties (ASSTC), which was basically a highly portable battlefield emergency room for the U.S. Army (see DN 6.7.1999, p. 85). Since the advent of this quick foldout facility in a composite box, the Army Medical Research and Materiel Command (Ft. Detrick, MD) has taken its ASSTC experience and folded it into a program with more potential—not only for improving care for forward-based troops, but civilian use as well in remote areas or during disaster relief operations.
The Future Medical Shelter System (FMSS) program seeks to develop a system that has more capability for modular growth, according to FMSS
The operating room area in the fully expanded MSU is 15.5 ft x22 ft. Because there are no folding panels for expansion, the side portions that slide outward have minimal sealing length along the perimeter.
Product Manager Mark Arnold. "A more modular system will be easier to plug together to expand upwards into a full hospital," he says, particularly regarding ease of hooking up utilities such as electricity, heating, and air conditioning. FMSS containers would conform to standard shipping container size (20 × 8 × 8 ft) and expand outward to an approximate 16 × 20 ft size (internally). On the other hand, ASSTC was essentially independent and not designed much for expansion.
"Most technologies for FMSS are advanced but proven and off-the-shelf. The key is integrating them into a nice package," says Arnold.
Vital needs include telemedicine provisions and compact electrical generators. Arnold notes even tie-down points have to be judiciously placed or it won't be possible to get two of the containers into a C-130 military transport, even though their size might be small enough. Then, once at the combat front, someone must load the containers onto MTVs (Medium Tactical Vehicles) for transport. To do this, they may use a frame on the truck similar to a tilting flatbed tow truck arrangement, or a crane that tilts and lifts the FMSS.
Working to bring about a workable FMSS are Mobile Medical International Corp. (MMIC; St. Johnsbury, VT) and the Oak Ridge Center for Manufacturing and Material Science(where ASSTC was developed). MMIC has experience in designing and producing a trailer size Mobile Surgery Unit that has been used for rural surgery and breast-cancer screening. The facility has communications provisions for telemedicine diagnosis. It is also used as a temporary facility during hospital renovations and for prison system medical care. Many of MSU's features, such as side compartments, are electrically driven to slide outward. They will be used on the smaller FMSS.
Initially, MMIC President Rick Cochran says, the FMSS structure will have an aluminum sheathing with a honeycomb core. "We are studying composites," he says, "but so far we have determined that although we might be able to cut weight by 25 to 30% with a composite substructure, the cost would double, and it isn't worth it."
Design concerns. The challenges engineers met on the MSU offer insight as to what will be needed for the military unit. "The biggest is making everything fit!" says Cochran. He specifically cites the complex electrical and HVAC (heating, ventilation, and air conditioning) systems. These must be stowed and then function after the side areas slide out from each side of the center section, forming the operational unit.
"Electrically, there are miles of cables carrying power and signals. We have 110V and low voltage, 3-phase, and 12V dc for battery back up," Cochran notes, "with limited space in the ceiling and floor to put it all." MMIC engineers came up with a folding track system for the cabling as well as the medical gas lines (oxygen, nitrogen, and suction) that "gently unfolds" as the sides deploy, according to Cochran. He notes the original non-metal trays kept breaking, so the designers turned to igus (East Providence, RI) for their Energy-Chain® aluminum cable carriers, which alleviated the problem.
The Future Medical Shelter System is a smaller, container-size unit based on technology proven in the larger MSU and ruggedized for military use.
With HVAC, engineers thought they had a good solution by putting the twin system (one for the operating room and one for the pre-op/recovery area) together with all the utilities in a compartment over the fifth wheel at the front of the trailer. While it did work, with 15 air exchanges per hour in the facility, they decided that locating the pre-op's HVAC unit next to the area it would serve eliminated long ducts, freeing up more space. With shorter runs, the system can run at lower air velocities, cutting down on noise. And now 25 air exchanges per hour are possible.
Out in the field. Operational concerns for reliability in critical circumstances also drove the design. Again Cochran notes the importance of electrical power and signals—for which four levels of redundancy were put in place. "We can run off utility power or with backup generator power. After that there is a UPS (uninterrupted power supply) from Invensys Powerware (Raleigh, NC), which uses eight 200A-hr 12V batteries and will keep critical circuits up for three to four hours. A separate four-battery bank is then available to maintain basic monitoring, recording, and portable suction functions in the facility."
Cochran says that with all this power, when an MSU is deployed, grounding is critical. "The first thing is to drive an 8-ft copper rod attached to the frame into the ground. There are also grounding wires in the electrical distribution system and the conduits are also tied together to meet the National Electric Code," he notes. "We end up with triple redundancy."
Military systems. In taking the technology and applying it to the FMSS requirements, Cochran says the task is to get it into a 20-ft container that meets ISO requirements. While the bathroom and pre-op areas are eliminated in the basic building block FMSS unit, getting the emergency generator and HVAC systems into this volume are still challenging. But he notes, developments are shrinking the generator sets continuously and making them quieter and more fuel efficient. Specific improvements include electronic control packages allowing lower speed operations under lighter electrical loads, and smaller diesel engines with economic, high-pressure fuel injection.
Communications electronics have also come down in size, Cochran adds. For example, in the MSU these are in a roughly 4- × 4- × 6-ft rack. "Now we can get the same functionality in perhaps a third that size," he notes.
Not having folding walls in the MSU will lead to advantages in adapting the deployment system to the FMSS. By having the side sections slide out, the seal length between the center section and the sides is minimal compared to folding panels that then need sealing to each other. Being airtight is important for medical contamination prevention and in the military to resist nuclear, chemical, and biological weapons. Positive internal pressure helps to maintain seal integrity as well. And, Mark Arnold adds, folding panels, particularly in overhead areas, are often a cause of personnel injuries when they accidentally open up or fail to latch.
With prototype FMSS availability targeted for late 2003, the Army's deployable medical systems may progress soon from tents and a collection of containers developed originally for general cargo use, to highly efficient and capable portable treatment and care centers—with likely application to civilian use in emergencies, disasters, and isolated locations.