Most emergency responders know that NH3 loves water and well-placed fog pattern will go a long way to “scrubbing” a large NH3 cloud. But after what we witnessed on Thursday morning, I do wonder if we all know the do’s and don’ts of using water around NH3. Yes, the incident Thursday was catastrophic and impacted hundreds of citizens and responders, but does this permit actions that are not in-line with “recognized practices”? This past week I was at a power plant working with them in their storage and handling of their NH3. In the power industry, their RAGAGEP of choice for their “covered process” is the Compressed Gas Association (CGA) 2.1 – Requirements for the Storage and Handling of Anhydrous Ammonia. And this RAGAGEP contains some specific advice on how to handle vapor releases from containers and some may find this advice very different in how they have been trained in ER training sessions…
4.2 Accidental release
4.2.1 In the event of an accidental release neither due to fire nor any other heat impingement, the concentration of ammonia vapor in the air can be reduced effectively by the use of adequate volumes of water applied through spray or fog nozzles. Downwind control should be achieved from a safe location, outside the cloud, by directing water fog nozzles toward the point of ammonia release from a downwind position in order to prevent the ammonia plume from moving away from the water fog. See 3.3.
4.2.2 Water should not be used on liquid ammonia spills. Water should only be directed in the form of fog or spray at the cloud emanating from the liquid pool. See 3.3.
4.2.3 In the event of a large vapor release from a container, THE TANK SHOULD NOT BE SPRAYED WITH WATER. Under these circumstances, water fog or spray should be applied to the vapor following the procedures outlined in 4.2.1.
The primary reason this is in the code is depending on the leak point, water could find its way inside the container and this would cause a significant pressure increase within the container which could have truly catastrophic consequences, making a bad situation much worse very quickly. As stated above, our water/fog should be directed to toward the release point from a DOWNWIND position. Essentially we should direct our water pattern into the path of the ammonia and let the ammonia drift into the water fog, WITHOUT getting water onto the container.
If the container is NOT leaking from a point of failure on the container (release via the RV is outside the scope of a “failed container” release) and is EXPOSED TO FIRE, the code states:
4.3 Fire exposure
If an ammonia container is exposed to fire and cannot be moved, WATER FOG OR SPRAY SHOULD BE USED TO COOL IT. Use caution if flame impinges on the container because violent rupture of the container is possible. If the fire cannot be controlled and it appears the tank can rupture, the surrounding area should be evacuated to a safe distance in all directions.
SPECIAL CARE should be taken to avoid water from entering the RV discharge vents; this is one reason why most RV design basis will include vent lines that extended 8-10′ from the top of the tank. This allows for proper relieving and venting of the NH3 gas while being able to apply water to the vessel with little risk of getting water into the vent pipes.