NO MATTER HOW SIMPLE a building looks on paper, there will always be challenges when designing and installing a sprinkler system. In some instances it is an odd storage configuration that baffles a designer, while for the installer the problem can be obstructions that appear in the field that were not shown on the plans. Designing and installing sprinkler systems for health care occupancies is no different — hospitals and health care facilities present challenges to the system designer that are often unique and require design practices that are outside of the norm.
One aspect of health care occupancies that presents design challenges is the magnetic resonance imaging (MRI) room. MRI technology is a medical imaging technique that allows doctors to examine a patient’s internal condition in greater detail than traditional methods such as x-ray technology. The magnets used in this technology are very powerful; typically, their strength falls in the 0.5-Tesla to 3.0-Tesla range, or 5,000 to 30,000 gauss. Considering that Earth’s magnetic field measures approximately 0.00005 Tesla (0.5 gauss), you can understand why care must be taken when using ferrous metals in rooms housing MRI technology.
Ferrous metals are iron materials or alloys containing iron that have inherent magnetic properties. Steel, which is the most common type of pipe used in sprinkler systems installed according to NFPA 13, Installation of Sprinkler System, is an alloy of carbon and iron. Depending upon the composition of the alloy and the ratio of elemental metals, steel pipe may or may not be magnetic. Traditionally, sprinkler systems have relied heavily on the use of ferrous materials.
Additionally, many system components, including the sprinkler, fittings, piping, hangers, and bracing assemblies, are constructed of ferrous materials or utilize ferrous subcomponents. These materials cannot be used in sprinkler systems in MRI rooms, since the magnetic power of the imaging machine is strong enough to pull them into the core of the magnet. In addition to the obvious safety concerns for patients and MRI technicians, the presence of ferrous materials can also throw off the imaging, leading to inaccurate results.
The prohibition of ferrous materials in these spaces requires sprinkler designers to rely on non-ferrous materials for their designs. The use of copper, brass, and stainless steel are common in MRI rooms, since these are not attracted to the imaging machine’s large magnets. While NFPA 13 does not mandate the use of specific metals or specially listed equipment in these spaces, some manufacturers already produce MRI-specific sprinkler equipment, or include information on the allowable use of their products in highly magnetized spaces in their product literature.
Whether these specially designed products are used or not, it is imperative that the sprinkler system designer work with the building’s owners and their engineering staff to come up with a solution that will not only comply with the sprinkler design standards, but also with the equipment being installed in these rooms. Failing to provide the right type of sprinkler system equipment in these spaces could lead to something much more costly than a few change orders — it could lead to injury or worse for people using the space.
Matt Klaus is principal fire protection engineer at NFPA and staff liaison for NFPA 13, 13R, & 13D.