Oklahoma City is the textbook case you point to when someone says a cheap fertilizer bomb cannot do catastrophic damage. A truck parked outside the Alfred P. Murrah Federal Building detonated a device made from agricultural ammonium nitrate and diesel fuel that killed 168 people and destroyed a large portion of the nine story building. The blast properties and the human cost of that attack still set the baseline for vehicle borne improvised explosive device planning.

The technical reason ammonium nitrate stays relevant is simple. In the right form and quantity it is energetic, easy to conceal, and widely available because it is a legitimate agricultural commodity. That combination makes it attractive to anyone who wants a high yield with low cost and low technical training. The National Academies reviewed precursor chemicals used in homemade explosives and explicitly placed ammonium nitrate and similar nitrate products in the highest priority group because of their history of use and availability. That is not academic. It is the baseline threat assessment.

Policy makers have not ignored the problem. Congress directed the Department of Homeland Security to develop an Ammonium Nitrate Security Program that would require registration of purchasers, point of sale checks, vetting against watchlists, record keeping and reporting of thefts and losses. DHS and its successor implementation elements issued proposed rulemaking and public materials laying out those measures. The intent is to block misappropriation while preserving legitimate commerce. The scope and the administrative costs are real, and the proposed program would regulate transactions at the point of sale and require two year recordkeeping among other controls.

Those proposals matter because the regulatory landscape has gaps. Chemical security authorities have shifted in recent years and some programs have lapsed or been restructured. For example, statutory authority for some chemical facility security rules lapsed in 2023, creating practical enforcement and coverage gaps that complicate a simple national fix. That absence changes how regulators and industry have to compensate.

History also shows the hazard is not just intentional terrorism. Storage and handling failures or criminal acts at facilities can produce equivalent devastation. The West, Texas fertilizer plant explosion demonstrated how large stockpiles of ammonium nitrate can be catastrophic when a fire reaches stored material. Investigators later concluded the fire that triggered the explosion was incendiary, and the event exposed failures in reporting, storage, and oversight that any security program must address.

So where does that leave us today, operationally? First, the fundamental threat calculus has not changed. Ammonium nitrate based explosives remain an accessible option for large scale damage. Second, the tools available to reduce that accessibility are known: registration and vetting at the point of sale, mandatory recordkeeping and reporting, thresholds for regulated concentrations, and physical and operational controls at storage sites. Third, implementation is hard because legitimate commercial use is widespread and because any regulation that is too blunt will harm farmers, landscapers, and industry. The National Academies studied those tradeoffs and emphasized that restricting precursors can reduce risk but cannot eliminate it, and that controls must be layered and targeted.

If you are a decision maker, here is the short, practical checklist to close the obvious gaps:

  • Implement a national point of sale registration and vetting system for bulk ammonium nitrate purchases, with clear thresholds for what counts as bulk. Make the process low friction for legitimate buyers but auditable and enforceable for sellers.
  • Require two year transaction records and mandatory immediate reporting of theft or loss. Audit a statistically significant sample of sellers annually.
  • Tighten storage standards and emergency response integration for facilities that store large quantities of nitrate products. Combine safety and security inspections so operators cannot hide poor practices behind regulatory silos.
  • Fund outreach and technical assistance for rural sellers and cooperatives so compliance does not become an untenable cost that drives noncompliance. The threat is national; the fixes must be practical for the people who rely on the product.
  • Maintain an intelligence and information sharing channel between law enforcement, CISA, state agricultural extensions, and industry so suspicious purchase patterns can be caught early. Do not wait for a headline.

There is no miracle technology that eliminates the threat while leaving supply chains unchanged. Physical security, sensible regulation, auditing, and targeted intelligence are the only way forward. Treat ammonium nitrate the way you treat any dual use material that has already shown it can be weaponized: assume it will be sought by bad actors and deny them the easy path. That approach is inconvenient. It is also realistic. The Oklahoma City attack is the lesson that will not bend to sentiment. We either build the controls that trade availability for safety or we repeat the same terrible outcomes in a new place and time.