At SMS, we review, prepare, and consult on site plans of all shapes and sizes. Whether it’s for government work or purely commercial, HD 1.1 or HD 1.4, we’ve seen almost everything. Continually we see the same errors pop up, specifically when the site plan needs to follow the “Contractor’s Safety Manual for Ammunition and Explosives,” or DoD 4145.26-M. These errors, oversights, or omissions can cause delays in site plan approval and stress for process owners and reviewers.

  1. Not taking into account fragmentation hazards

When dealing with HD 1.1 articles and substances, fragmentation is a major concern. For quantities under 30,000 pounds the distance for IBD and PTRD is controlled by debris and fragments (DoD 4145 para C5.5.1). Above this quantity, fragments are still an issue, but the major hazard in the far field is overpressure. There are two major types of fragmentation to consider: primary fragments and secondary fragments.

Primary fragments

These fragments are generally in intimate contact with the article and move at speeds of thousands of feet per second. If these fragments are not properly stopped by a qualified barricade or other surface, then they must be taken into account for quantity distance (QD) purposes. QD calculations for primary fragments are found in the “Open” column of Table AP2.T2 of DoD 4145. Primary fragmentation is the primary hazard in HD 1.1 quantities up to 450 pounds.

Secondary fragments

 Tables, chairs, desks, building debris, etc. are considered secondary fragments, and are sometimes referred to as hazardous debris. These fragments move initially at hundreds of feet per second and are not stopped by barricading because the debris can be lobbed great distances. When primary fragments are stopped, but secondary fragments are still a concern, then the “Structure” column of Table AP2.T2 is used for QD calculations. Above 450 pounds of HD 1.1, the differentiation between primary and secondary fragments is no longer made.

Hazardous fragment distance, or HFD, is highly dependent on the quantity of material, the type of material, the PES-ES pair, and a few other factors. The error we see most frequently is only taking into account overpressure hazards for HD 1.1 and not fragments. Additional guidance for this concept is found in paragraph C5.8 of DoD 4145.

  1. Incorrect application of ILD and IBD

Businesses and processes change over the years. Increasingly, we are noticing an uptick in companies that have merged, split, been bought, or sold off property for a variety of reasons. This can create significant site planning issues in some cases. IBD, or inhabited building distance, is the distance required from an explosive location and an exposed site unrelated to the explosives mission. ILD, or intraline distance, is the distance required between two sites that are related to the explosives mission. When a building that was previously “related to the explosives mission” is sold off, it is now considered outside of the plant boundary, to which IBD is required. Even if the purchasing company is also an explosives manufacturer, the two companies remain completely separate in the eyes of the reviewer. Where ILD was once the requirement, IBD now governs. This can severely limit the capacity of both buildings and in some cases, cause the operations to be relocated. Prior to any purchasing or selling deals, SMS highly recommends analyzing the implications to the facility site plan.

  1. Disregarding HD mixing rules

Energetic processes often require multiple types of substances and mixtures to make an article function as intended. Time delays, igniters, flight termination devices, warheads, inflators, and other components often make up a final product. Each of these components contains a different material designed to function in a different way, and when they are all stored or processed together, certain rules apply.

Rules for mixed HD storage are found in paragraph C5.3.2 of DoD 4145. Perhaps the most common mistake is when HD 1.1 is stored with other hazard divisions. HD 1.3 is the hazard division containing propellants or other articles where the primary hazard is a mass fire. But some HD 1.3, when boosted by a detonating donor charge, can act as an HD 1.1, or mass detonating. This is why when HD 1.1 and HD 1.3 are stored or processed together, the entire mixture is summed and treated as HD 1.1. For example, if you have 500 pounds of propellant together with 1 pound of HD 1.1, that entire mixture would be treated as 501 pounds of HD 1.1 for an IBD distance requirement of 1,250 feet. Compare this to as little as 200 feet separation distance for the single pound of HD 1.1 or 75 feet for just the HD 1.3 and you can see how disregarding this mixing rule can cripple a process. When determining net explosive weight for QD (NEWQD) it is imperative to factor in all forms of HD mixing located in and around the PES.

Facility siting based on DoD 4145 can be a complex process for some sites. Finding and correcting errors early on in the preparation, preferably before a site is even constructed, will allow for greater operational flexibility and most importantly, provide a safe working environment for employees and keep the public safe.

If you have any questions about your site plan or want to schedule a review, please contact SMS.