A NFPA 1123(2000) question?

[SoonerKid]

A.2.6.1.2
Aboveground racks should be constructed to withstand a catastrophic
malfunction in a mortar. Wooden racks should have sides and bottom plates of at least 2 in. (5 cm) nominal thickness. The racks should be boxed on both sides at the top and bottom by 1 in. x 6 in. (2.5 cm x 15 cm) nominal thickness boards or 1/2 in. (1.3 cm) thick plywood. Blocks of 2 in. (5 cm) nominal thickness should be attached to the horizontal boards between each mortar of inside diameter greater than 3 in. (76 mm). Boards should be fastened by nails, screws, or other fasteners that penetrate a minimum of 1 in. (2.5 cm) into the member to which a board is attached. Racks should be secured to prevent tipping over by attaching stakes or spikes driven into the ground, banding, using A-frames, or other equivalent means. Aboveground wood frame mortar racks with lightweight mortar materials such as paper, HDPE, or fiberglass generally will not withstand a catastrophic aerial shell malfunction in a mortar.

Ok most of the 1.3g racks I've seen didn't have 2 x's in between the mortars. There was maybe a 3/4 board in between the mortars if any. I know this probably makes them safer but i imagine it makes the racks allot heavier.

EDIT: OK my bad i just realized this was part of the Appendix and was for informational purposes but this still is a good question on whether to have space between the mortars.

[lamrith]

The important thing is the SIZE of the mortar. Notice they do not say it is in a ratio, Xcm per inch Diam.. Anything under 3" and they do not have those rules.

I did not realise we had to have such a thick spacer between mortars. I will have to bring tht up at the next class. Thanks for the teacher stumping question!!:twisted:

[SoonerKid]

At the end of that it also states that it generaly won't withstand catastrophic aerial shell malfunction. So i guess there saying build the rack as strong as possible.

[wrtiii]

In my experience, putting wood between the tubes only produces shrapnel. HDPE is not intended to contain the explosion, but is used because it ruptures gracefully (indeed, often artistically) and produces no shrapnel. However, the wood on the rack does indeed become shrapnel, and I know of one incident where a pyrotechnician ended up in the hospital having the splinters picked out of him (but fortunately no other injuries) - and that was a 3" shell. So I would say NOT to add extra wood, and the bigger the shell, the less I would want extra wood. Shells that are sensitive (large salutes) we usually fire from separate, in-ground mortars.

[carp]

The individual separation is intended to help reduce the risk of mortars spilling out of the rack. If i can find them I will post a link to some pictures where the benefit of doing this is shown. I use 3/4" plywood for my top, bottom, and middle side boards. California also has laws where the separation must be equal to the diameter of the mortars.

Here's a link:
http://groups.msn.com/NorthEastOhioPyro/spencer2003after.msnw?action=ShowPhoto&PhotoID=750

Check out the rest of the pics too. They also show the shrapnel that was mentioned and pictures of the damage. Both shooters got a trip to the hospital. Here is the description of the event.

http://groups.msn.com/NorthEastOhioPyro/general.msnw?action=get_message&mview=0&ID_Message=14&LastModified=4675429501245048025

Some people glue and screw or nail. Some like to omit the glue to let the racks give a little.

I like Advanced Technique Fireworks aluminum racks. Each mortar is individually secured by HDPE clamp rings.

[pyrocasto]

I think nails should never be used in building racks. They can come out much easier over time and just make it that much more dangerous.

Screws and good wood, that rack isnt coming apart...

[dfluke]

I was reading on another website and this builder of mortar racks suggested the basic box like frame, but to also screw down the HDPE tubes from the bottom of the rack.

So, in other words the screw would go into the bottom of the base board through the base and into a wood plug which resides in each mortar.

Now I planned on making wooden plugs for my hdpe mortars and screwing them in by placing screws on each side to hold in the plug.

I would think that by screwing the plug/hdpe tube into the base of the rack that there would be too much rigidity. However, by simply placing the tubes into the rack without fastening them down might present a hazard correct? Would the tubes bounce out or is simply placing them into the rack good enough?

[SoonerKid]

dfluke i did that exact thing on my 1.4g racks(running a screw from underneath the base up into the plug).
IMO it wouldn't be very safe to screw 1.3g tubes down incase of a hangfire or lodged shell! Im pretty sure there left loose.

[wrtiii]

The racks I've used in professional shoots (supplied by the company) do not have the mortars fastened into the racks other than by the friction between the sides and the spacers. I have never seen one that moved during firing. Occasionally during setup we will see one tube that came up slightly, usually because somebody grabbed the tube when picking up the rack, but we just shove it back down before loading. We have never had a problem with this.

If something catastrophic happens, I can't believe that having a screw into the bottom plug from either the side or the bottom is going to help.

[Pyroman6000]

All of our tubes are screwed to the bases plate from the bottom up. Not only does this elininate the need for a toe board, but if there is a cato, the tubes will not simply spill out.

IMO, toe and middle boards are a bad idea, as that's where the mortar usually ruptures whae a detonation occurrs. One of our shooters carries the scars form a butt load ( literally!!)of wooden shrapnel that came from a 3" rack full of salutes that had a detonation. the original blast pinched off and damaged adjacent tubes and also lit the shells in them! Wood DOES NOT show up on X-rays!!!! The hospital had to probe EVERY wound for debris... it was excruciatingly painful according to him. To avoid this outcome NEVER put yourself broadside to a rack with a lit shell in it. We train our shooters to light and move on down the line to put themselves past the ends of the racks( the strongest point).

The other thing is to use the minimum of wood in building the racks, ours have bottom plates, uprights at the end, and 1x slats on each side at the top to hold the ends together, and keep the mortars upright. Aside from the legs, that's it! Other than that top slat, which is unavoidable, there is NO wood alongside the mortars. We use poly and paper only. When a tube blows the energy is dispersed to the sides. Any wood wood in the way simply becomes shrapnel. Due to the way our racks are built, it is extremely rare that one of the racks blows apart partially or entirely. Usually the tube just blows-sometimes crimping or otherwise damaging the one next to it. If the explosive force has to blow through a structural member, the chances of a total rack failure go way up.

Interestingly, the only racks we have that have a spacer between the tubes ARE the 2.5 and 3"ers! I think he bought those to use for finale's to help keep the leaders away from the mouths of the tubes. They are also a HELL of a lot easier to foil individually! Nothing like walking up on a rack full of shells with comets and have one go up in your face because the comet got ingited by flaming debris!

With that much separation, those Kalifornia racks must be HUGE and really heavy! That or they're only a few tubes, meaning there are that many more to lug around and set up!

A rack that has a malfunction occur is avoided for the rest of the show. If there is an extra pyro available, it is his/her job to watch the shooters and look for shells that don't leave, blowouts, low breaks and duds. It's the jobs of all the lighters to watch each others backs also.