Why Phosphoric Acid is in the News

Phosphoric acid is used across a wide range of products, mostly to add acidity. It plays that role in popular cola-style sodas and in agriculture as a soil stabilizer and fertilizer. It is used in ceramic binding, fire-control agents and make-up.

It can also kick off a hazmat response when released.

In late April, hazmat teams were called to an Orange County, Calif. aerospace facility when five gallons of phosphoric acid spilled. Several news agencies reported that the facility floor was designed to absorb the acid. Employees closed the door to the room and evacuated the facility.

One employee suffered skin irritation and was transported for evaluation. Firefighters also evacuated neighboring businesses.

Learn more about the Orange County Fire Authroity’s hazmat team here.

Phosphoric acid can be transported in both solid and liquid by pipeline, rail and truck. In December 2019, a semi rolled over on I-80 in Illinois and began leaking the material. There, about 100 gallons leaked, closing the interstate for nearly a day, as CBS reported.

And in 2020, hazmat teams were called when it was leaking from the ground and ignited once it reacted with the air. That land was once a fruit orchard and the phosphoric acid may have been held in the ground since that time.

When stockpiled, it can trigger significant federal fines, as J.R. Simplot learned in 2020.

At 20°C at a concentration between 50% and 75% it is an odorless, colorless liquid. At 85% strength it becomes syrupy, and turns to crystals at 100%. It is usually transported at 85%.

On its own, the corrosive will cause burns to skin, but remains stable and nonflammable. But when heated it can produce toxic fumes and ignite other combustibles. And, of course, when it contacts metal, can emit flammable hydrogen gas — and it is an explosive and fire hazard when mixed with incompatible materials.

When it does catch fire, ERG says to isolate the area for a half mile in all directions and consider evacuating that area.

NIOSH recommends a supplied air source with full face piece for any concentrations of phosphoric acid between 25 and 1,000 micrograms per cubic meter. It calls for full SCBA for levels above 1,000 or when entering in an emergency or suspected IDLH environment. ERDSS puts TWA at 0.25 ppm and considers an IDLH at 249.5 ppm. 

For more on when firefighters can enter a hazmat scene with normal PPE and when they need to activate a hazmat team, read “Quick Guide: When to Call Hazmat Teams, and When not to.”

And here’s a deep dive into the chemical properties, uses and precautions put out by PubChem.

Phosphoric acid may not leak and spill with the frequency of, say, chlorine. However, it is used in an array of consumer and industrial products and is dangerous enough to keep fresh on how to handle it when it does escape into the environment.

Phosphoric Acid Properties:

Chemical formula: H3O4P
CAS number: 7664-38-2
pH: 1.5
Vapor pressure: 0.03 mmHg
Vapor density: 3.4

Response Tips:

  • Phosphoric acid can be detected in the field using pH paper, colorimetric tubes and detectors using flame spectrometry.
  • When neutralizing, add neutralizer slowly and check the pH frequently to ensure you are not overshooting the target pH.
  • Ensure your PPE and absorbent materials are compatible with the product.

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