Small-scale Testing, Large-scale Benefits

FM Approvals: Small-scale Testing, Large-scale Benefits

Water mist standard to be updated with protocols for scaled testing and new data center applications

This year marks the twentieth anniversary of the first FM Approved water mist system. At 300 pages, Approval Standard 5560, Water Mist Systems, is the most comprehensive standard in the world for water mist fire protection testing and includes detailed fire test protocols for a wide range of water mist system applications, each contained in separate appendices.

FM Approvals will revise Standard 5560 this year to incorporate new test protocols for water mist fire protection systems. One of these new test protocols will provide a methodology for using scaled-down fire testing of water mist systems to simulate full-scale volumes. This new approach promises to help reduce the time and costs required to develop and test new types of water mist fire protection systems.

The revision to Standard 5560 will also incorporate two new test protocols for water mist systems intended for the protection of above and below raised floors in data center server rooms.

The new test protocols, based on research conducted in conjunction with industry partners at the FM Global Research Campus in West Glocester, Rhode Island, is intended to address real-world conditions found in modern data centers, including the challenge of delivering fire suppression in the face of active ventilation.

Benefits of scaled water mist testing

Currently, the scope section of Standard 5560 notes that “FM Approvals has determined that water mist systems shall be FM Approved for the protection of specific applications and specific protected area volumes. Extrapolation beyond the volumes which were tested is not permitted except where explicitly noted.”

This stipulation of the standard has meant, for instance, that manufacturers of water mist fire protection systems have had to resubmit their systems for Approval testing each time they wish to use the system for a larger volume e.g., not exceeding 2,800 ft3 (80 m3), not exceeding 9,200 ft.3 (260-m3). In addition, Approval testing under Standard 5560 requires full-scale fire tests for each volume increment.

“Historically, we’ve required manufacturers to retest for each new volume,” notes Rich Ferron, FM Approvals operations vice president and manager of testing and certification. “Sometimes manufacturers have had to return not long after receiving their initial product Approval because the customer requires a system for a larger volume. And, it’s not just the Approval testing, it’s the development work and characterization of the system in order to optimize its performance. That all requires time and money.”

He adds, “In some cases, the time and expense of development and testing has limited the growth of the water mist industry for some niche applications, and that’s troublesome. Our goals are always to provide the widest possible range of FM Approved loss prevention solutions and to promote increased availability in local markets globally. We believe our new scaled testing methodology has the potential to relieve some of the pressure on water mist system manufacturers.”

Potential benefits as a result of scaled water mist testing:

  • Potential reduction in cycle time and cost to get the system FM Approved
  • Potential significant reduction in manufacturer’s R&D time and costs due to screening test availability
  • Potential reduction in required number of reduced-scale tests in the future (after gaining some experience)
  • Ultimately increase the number of certified water mist systems and applications

As early as 2008, FM Global researchers published a paper detailing experiments conducted at the FM Global Research Campus showing that water mist suppression and extinguishment of enclosure fires can be scaled at a 3-to-1 ratio, holding promise for the use of physical modeling in the evaluation of water mist fire protection systems.

This work continued, with FM Global and FM Approvals investigating ways to characterize nozzle water droplet size, distribution, momentum and spray angle/pattern. A scaling methodology was developed that allowed large-scale fire tests to be reliably scaled down by one-half or one-third.

Recently, final validation testing was conducted that demonstrated that an existing FM Approved water mist system for the protection of a 9,200 ft.3 (260-m3) machinery enclosure could be replicated in a one-half scale enclosure.

“We used half-scale nozzles and half-scale pool and spray fires in a half-scale enclosure and the results have been comparable to the full-scale results for all scenarios,” explains FM Global principal research scientist Dr. Hong-Zeng (Bert) Yu. “Compared to the sprinkler industry, companies producing water mist fire protection systems are relatively new. We believe our new methodology for scaled testing will help reduce the cost of expanding the industry and applications.”

He continues, “Under the new test methodology, the manufacturer will provide us with the full-scale nozzle and the scaled nozzle, and the spray from each will be characterized to see if they match. If so, tests will be conducted in a scaled-down enclosure, saving time and money.”

The water mist scaling methodology will be added this year as a new appendix to Standard 5560. The new process for Approval will include these steps:

  • Manufacturer applies for Approval with parameters for full-scale protection.
  • Manufacturer submits full-scale nozzle and scaled-down nozzle for spray measurements (i.e., characterization) to ensure they meet the scaling requirements.
  • Fire testing is conducted with scaleddown nozzles in scaled-down enclosure (volume).
  • Approval is granted for full-scale protection by scaling up the scaleddown test results according to various scaling relationships.

According to Jonathan Carpenter, an advanced engineer for FM Approvals fire protection group, the new test methodology will apply to total flooding applications only. “We’re talking about machinery and combustion turbines in enclosed volumes which are considered total flooding applications,” he notes. “Those applications make up at least half, maybe more, of the FM Approved water mist systems in the Approval Guide today. This gives these manufacturers and others new flexibility when seeking Approval for other enclosure sizes.”

Manufacturer perspective

“From a high-level standpoint, this is an exciting development in the water mist community,” says Brian J. Stumm, director of engineering for Marioff, makers of water mist fire protection systems. “We are approaching this new development with an open mind. We’re very happy that there’s more focus on providing innovative ways to test water mist systems at a lower cost and potentially faster. If this enables us to get more products under the FM APPROVED mark, then that helps the industry.”

James Golinveaux, senior fellow of water suppression products at Tyco Fire Protection Products, shares a similar view. “I’m aware of this effort and we’re fans of the reduced-scale testing concept. Anything that reduces our costs will ultimately help reduce the cost for our customers. If FM Approvals and FM Global believe in it, that makes us pretty confident that it’s sound technology.”

New Test Protocols Offer Options for Data Center Fire Protection

In March, FM Approvals introduced two new fire test protocols in draft form for use in testing water mist fire protection systems and to protect areas above and below raised floors in data centers. These draft test protocols will be included in the revision of Approval Standard 5560, Water Mist Systems, to be released by end of 2015.

While the debate continues over the virtues of raised floors versus slab floors in data center construction, the fact remains that close to 90 percent of the world’s existing data centers use raised floors, according to the Uptime Institute. Traditionally, raised floors have been favored in data centers because they provide a convenient path for the air needed to cool hot servers, route bulky network and power cables, provide a grounding grid, and a pathway for plumbing where liquid cooling is required.

Safeguarding the data center environment is critical to business continuity and data asset protection. Data center downtime costs approximately US$8,000 per minute, according to a 2013 study. At the same time, fire detection and suppression in data centers is particularly challenging due to a high volume of airflow needed for cooling, high power density, sensitive electrical equipment, metal-shielded fire loads, raised floors, hot/cold aisle containment curtains and other factors.

To minimize the chance of accidental water discharge, fire protection systems for data centers typically feature a double interlock preaction sprinkler system, sometimes in combination with an alternative suppression system such as clean agent, inert gas or water mist.

The two new FM Approvals draft standards for use in testing water mist systems were developed in partnership with two leading suppliers of water mist fire protection systems, Marioff Corporation Oy (Marioff) and Tyco Fire Protection Products, in direct response to the need identified at FM Global client locations. As a result of research conducted at the FM Global Research Campus, fire test protocols were developed to address two common data center fire scenarios.

Data Processing Equipment Rooms – Above Raised Floor

This fire test protocol can be used to assess water mist fire protection systems in open server rooms—and/or within hot and cold aisle containment areas—where there is active forced ventilation, significant amounts of cabling and interlocked dry pipe/preaction configurations. The protocol may also be used to test systems as wet systems only, and will be listed as such in the Approval Guide, a web-based publication of FM Approvals.

The fire tests for this test protocol will be conducted using a mock-up representing a small section of a data hall at the FM Global Research Campus. The mock-up includes a one-meter-high raised floor with perforations for air flow, two rows of server cabinet mock-ups, and vertical and horizontal cable bundles in metal cable trays. The cables have a polyethylene outer jacket and high-density polyethylene insulation on copper wires inside the jacket.

A roll of cotton soaked with gasoline is used as an ignition source at the base of the vertical cable bundle. Blowers and fans are used to simulate server room forced ventilation from the floor and through the sever mock-ups. Protection is deemed adequate if the fire does not spread to either end of the horizontal cable tray and the fire is extinguished within 30 minutes after first nozzle activation. In addition, a steel angle at the ceiling—simulating a support beam—must not exceed 1000o F (538o C).

Data Processing Equipment Rooms – Below Raised Floor

This fire test protocol assesses water mist systems for fire protection below data center raised floors where there is active forced ventilation, single or double-tiered cable trays, and an interlocked dry pipe/preaction configuration. Again, if the water mist system is tested on a wet system only, this will be noted in the Approval Guide. In this fire test protocol, a mock-up of a one-meter-high raised floor is used, including ventilated floor grating and one or two metal cable trays, depending on the desired test scenario. Forced ventilation is simulated and the same ignition source is used as in the above raised floor protocol. One gasoline soaked cotton roll is used for the single tray test and two for the double tray test.

Protection is deemed adequate if fire does not spread to the opposite end of the cable tray, the fire is extinguished within 30 minutes from first nozzle activation, and gas temperature does not exceed 1000o F (538o C). The water mist system manufacturer may choose to select the double-tier cable tray scenario if the single-tier test is successful. Single-and double-tiered ratings will be noted in the Approval Guide.

Marioff and Tyco: Partners in Protocol Development

Both Marioff and Tyco Fire Protection Products contributed their water mist systems and engineering expertise to the development of the new test protocols. “Data centers are, of course, a key infrastructure worldwide that is growing in dominance,” says Brian J. Stumm, director of engineering for Marioff. “It’s great that FM Global and FM Approvals recognize that things have changed in that industry and are providing new tools to address the fire loads. It will be interesting to see how other approval bodies around the world react to this development.”

“This is a great example where FM Global and FM Approvals reach out to industry for participation in new research that leads to a new product application,” notes James Golinveaux, senior fellow of water suppression products at Tyco Fire Protection Products. “The result will be a system that is available to anyone in the market, worldwide. It’s truly a win for all involved.”