plastic mortars continues unabated. In making their points for and against, many arguments are focusing on only certain strengths and weaknesses and only for what- ever application the individual happens to use themselves. While arguing the physical properties of each is important, it is often forgotten as to who, what, where, when, how and how often these mortars have been or will be used by people.
No one type of mortar will be the best for all applications under all conditions by all op- erators. Economics have the most to do with the choice and that is often determined by availability. Close behind is the personal preferences of each operator as to how they wish to shoot their show, the terrain and climate of their area, and the amount of space and travel they do between shows. So too the number of shows, the sizes and the methods used.
The risks associated with using different materials and constructions are often as- sumed and are based on simply what has been done in the past. Most of the materials have not been manufactured for use in the pyrotechnic industry but rather h a s been used in plumbing, oil and gas, paper or other uses and have been adapted to fireworks use.
Thus most of the hard scientific data regard- ing the properties of each has been basic physical properties of the substances them- selves for their primary use. Tensile strengths, bursting pressures, temperature and moisture variations, flow rates, weight capacity and so on are important, but only when taken in context with the many other variables when used for shooting displays.
What type of plugs are used? How are the mortars installed? How old is the substance? What was it designed for? Is it new or used? What is the source? How h a s it been stored? Cleaned? How long will it be used? What other factors h a s it been exposed to?
How will it be used? Will the shells used in the mortars be hand or electronically fired? What kind of climate conditions? How will they be placed? Above ground in racks? What types of racks? In the ground? What type of soil? How often will they be used? How close will the operators be? The crowd?
Where will the mortars be stored? Indoors? Outdoors? What climate? What types of shells will be fired from them? Salutes? Color? Multi break? Experimental? Under what conditions?
STEEL MORTARS
Each h a s pluses. Steel h a s been used for generations. It's strong, stands up to lots of abuse and will last a long time. Some opera- tors even brag about being so confident in their mortars they'll stand right next to every shell that goes up!
But steel means massive amounts of weight and high cost which mean that small opera- tors or those who use electric firing where hundreds of mortars are required will be less likely to want to use steel mortars. They are also hard to clean and in humid climates tend to rust. There are some questions on some types of seamed pipe and the thinwall steel.
The other problem is that one manufacturer's well made steel mortar is not the same as another's. There are no standards for plugs or welds. There are no standards for aging or cleaning. Some operators will pick up inferior grades or used pipe to make into mortars. They'll use cast iron pipe and even use screw on plumbing plugs!
Clearly the biggest plus for steel is its strength, when properly constructed. But just as dashboards are no longer hard steel, it doesn't mean that strength guarantees automatic safety. When steel does burst, rare but more frequently with more use and more powerful shells, it is more dangerous. The shrapnel from a steel mortar carries a long
distance and can be as deadly as a claymore mine.
This is especially true when the mortar is above ground in a rack. In my opinion, even with the proposed NFPA 1123 guidelines of 150 feet distance from the crowds for a 3" mortar, that is taking too much risk.
Still, I feel that for hand firing, and for large shells and experimental shells, steel that is properly made and placed is the only way to go.
PAPER MORTARS
As for cardboard it's light and it's cheap. Available in the last few decades, mostly be- cause of the increase in the use of cardboard tubes for rolling paper and plastics on, its been great for barrage and finale racks and electronically fired shells. They certainly are not to be used for individual hand firing, al- though many operators do it.
Cardboard's drawbacks are that it will wear out quickly as the core burns out and wid- ens, and the plug is pushed out, if the moisture and handling don't get to it first. They've been accepted for finale racks and barrages as shows grew in size and the GRAND FINALE grew in popularity.
One major drawback is, cardboard was made to hold massive rolls of weight and the stan- dards are for that. Some are weaker and should only be used to fire one or two times. And again the plugs and how they are in- stalled can be a problem
While cardboard shrapnel is not as danger- ous and won't carry as far, I feel that it can cause damage. As larger bores became avail- able we now see 8", 10" and 12" cardboard mortars on the market, with operators plac- ing it above ground. Plugs and racks can blow out, racks and mortars tip over.
Cardboard does have it's place. Salutes, I feel, should be fired from it, as the shrapnel
from a buried cardboard mortar that has a shell detonate is not likely to be seriously harmful to even the operator. Finale and bar- rage racks properly made, secured and sand- bagged, with enough distance from the op- erator and the crowd, are also the most eco- nomical and feasible way to go.
HDPE MORTARS
Plastic is another matter. The first efforts with PVC, which is readily available and still used by some, have met with failure. PVC is cheap and light, but very brittle and doesn't stand up to handling abuse as well as card- board mortars.
The other efforts with HDPE have met with greater success. Slightly more expensive than cardboard but not as easy to find, its pluses are it is light, won't rust and is easy to keep clean. Wooden plugs are easy to install and if cut long enough even when the plug blows out it can be replaced by cutting off the end of the mortar and putting a new plug in. Storage is a breeze as each size will fit into the next and moisture isn't a problem.
It can be placed in racks, buried, or put in troughs. For electronic firing, it will be easier to set up and care for than steel, but last longer than cardboard. Unlike PVC, it is not as brittle, even when the temperature is be- low zero. When a shell detonates in it, early tests show it will only split or bend.
HDPE has drawbacks though. Made for fluids to flow through, the inside diameter is not always exact to shell specifications, which also vary from supplier to supplier and type to type. If stored outdoors, some legitimate doubts are raised regarding how pliable if left in the sun or extreme heat, as in the south- west or north, that would freeze and thaw the plugs and rust the fasteners.
And j u s t as with cardboard, I feel that HDPE should only be used for finale and barrage racks and electronic firing, never hand fired.