CMDA & ESFR Options for Lumber Storage?

2/15/2021

We have a 40-foot tall steel construction building, with lumber strapped and stacked, stored in 20-foot high solid piles.

The building is unheated. The building owner has been told by another fire sprinkler contractor that this will require ESFR sprinklers. The owner would prefer a dry pipe system.

We have researched NFPA 13, 2019 edition. It looks as if Chapters 20 and 21 will allow a dry pipe system for this application using CMDA sprinklers.

Anyone else have experience with a scenario like this? What path would you recommend?

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4 Comments

Franck

2/15/2021 10:57:36 am

The issue may come from the height of the building and the clearance between the top of storage and building roof.

When the clearance is too high (excessive clearance), then other adverse effect may occur: delay in the activation of sprinkler heads (resulting on the operation of more sprinklers at the ceiling level), larger heat plume impact at the ceiling level (resulting again on the operation of more sprinklers at the ceiling level), poor penetration effect to the fire area and possible inadequate droplet size distribution when the water distribution pattern reaches the fire area (the fire plume that the sprinkler discharge must penetrate to reach the burning materials increases).
Most performance tests are realized with a clearance between 1.8 and 3 m (6 to 10 feet), and the ideal target is between 0.9 m (3 ft) and 3 m (10 ft).

The maximum allowed clearance for CMDA sprinklers (Control Mode Density/Area) (standard spray sprinklers) to storage should be:
• 6.1 m (20 ft) for palletized, solid-piled, bin box, shelf, or back to back shelf storage of Class I to IV commodities and Group A Plastic.
• 6.1 m (20 ft) for rack storage up to 7.6 m (25 ft) of Class I to IV commodities
• 3.1 m (10 ft) for rack storage of Group A plastic commodities and for rack storage above 7.6 m (25 ft) of Class I to IV commodities.

The storage protection requirements for a given height of storage in a given height of building are also implicitly adequate to protect any lesser storage height in that building. This requirement is necessary as within a warehouse, the storage is never completely full and storage height can fluctuate widely in both the short term and the long term.

When the actual clearance exceeds the limitations indicated above, the situation is at higher risk and complementary measures should be considered to avoid resulting in an inadequately protected storage configuration.

So in your case, 20 ft storage inside a 40 ft building, you may still be in good conditions for an adequate fire protection system.

You can use the CMDA curves for a class III occupancy, with adding 30% to the design area for a dry system.

I would suggest you to use high temperature sprinklers in your case, becuase of the high clearance and the dry pipe system, to avoid opening too many heads before the operation of your system.

You can also use CMSA protection with a dry system (table 22.2 in 2019 Edition)

Be aware about the possible size limitation for the dry pipe system (you need water to be delivered to the most remote point in less than 1 minute!), depending on the size of the building (square footage).

Just one comment: is the roof flat ? Remember that if the roof has a slop exceeding 1:6 (16.7%), then NFPA 13 does not apply for storage occupancies.

Jesse

2/15/2021 01:21:43 pm

Back in the day, I inspected a lot of forest products workers for insurance. 2016 NFPA 13 Table A 5.6.3.3 notes storage of dimensional lumber as a Class III Commodity. So you can protect it as you would any C-III. Dry ESFR is relatively new to our world, so pay attention to 13s restrictions and allowances.

Also, note that there are some insurers that impose more stringent classifications on the product. I know of 3 major High Protected Risk insurers that designate "stuck" lumber as C-IV Commodity. "Stuck" lumber consists of lumber stacks that have 1" sticks between each stacking tier. This is done downstream of the first bin sorter in the mill, and upstream from the kilns. The purpose is to allow for even drying of the stack by allowing air movement in the kiln across all surfaces of the dimensional lumber boards, as opposed to just the exterior of the solid unit load. This is great for the drying process. But frequently, mills leave the sticks in for quite some time in storage after the kilns. Now we have kiln dried lumber with a moisture content conducive to combustion with the ability to get convective air all around to aid pyrolysis and combustion. Think of stacks of pallets burning as opposed to solid unit load.

ESFR gives you most flexibility if you can do it. But if you go CMDA or CMSA and design for a C-III density and then find out their insurer won't accept it and it needs to be reinforce to a C-IV density, you'll have a really unhappy client.

Hope this helps. J

Bubaface

2/18/2021 06:11:55 am

Thanks for the input!

Jesse

2/18/2021 11:32:50 am

You got it!

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