1984 - Rio Neuquen

The Argentine M/V Rio Neuquen arrived alongside city dock 9 in the Port of Houston, Texas on the morning of July 27, 1984. Longshoremen were unloading the last container in the number two 'tween deck hold (UTD) when the container exploded. The 20-foot steel container bulged and strained at the seams blowing both doors from the hinges and littering the deck with cargo. One man was killed by a flying container door and the other men in the hold and on deck were exposed to a strong garlic-scented gas. The first responders to arrive after the explosion were from the Houston City Fire Department and the U.S. Coast Guard from the Port Safety Station in Houston. Initially, no hazardous materials were reported to be aboard and the crew could not account for the source of the explosion. The dead and injured were removed from the hold, but the presence of the irritating gas aroused suspicion that the situation was more serious than was apparent. The hold and vessel were cleared of response personnel and bystanders, but the captain and crew of the ship refused to leave.

The Argentine M/V Rio Neuquen arrived alongside city dock 9 in the Port of Houston, Texas on the morning of July 27, 1984. Longshoremen were unloading the last container in the number two 'tween deck hold (UTD) when the container exploded. The 20-foot steel container bulged and strained at the seams blowing both doors from the hinges and littering the deck with cargo. One man was killed by a flying container door and the other men in the hold and on deck were exposed to a strong garlic-scented gas. The first responders to arrive after the explosion were from the Houston City Fire Department and the U.S. Coast Guard from the Port Safety Station in Houston. Initially, no hazardous materials were reported to be aboard and the crew could not account for the source of the explosion. The dead and injured were removed from the hold, but the presence of the irritating gas aroused suspicion that the situation was more serious than was apparent. The hold and vessel were cleared of response personnel and bystanders, but the captain and crew of the ship refused to leave.

A chemical response team from the fire brigade entered the hold in protective equipment and found the containers' cargo to be cardboard boxes, each containing 14 aluminium flasks. All seemed intact, including the flasks strewn about on deck. An identification of the cardboard boxes identified the product as Gastoxin with aluminium phosphide listed as the active ingredient. However, early information from the scene was conflicting or incorrect and the product was variously reported as aluminium sulfide and ammonium phosphide as well as aluminium phosphide.

Aluminium phosphide is a toxic biocide used in fumigation for the control of insects and rodent pests. It reacts with water or atmospheric moisture to emit phosphine (PH3) according to the reaction: AlP + 3H2O ---> Al(OH)3 + PH3. Phosphine is a colourless gas with a garlic-like odour. It has a TLV-TWA of 0.3ppm, a TLV-STEL of 1.0ppm and an IDLH of 200ppm. It is spontaneously flammable and is often contaminated by small amounts of diphosphane that is likely to auto-ignite in air (auto-ignition temperature reported for phosphine is 38ºC) and cause an explosion even at ambient temperature in an enclosed or confined space. Aluminium phosphide has a low aquatic toxicity due to its reaction with water to form phosphine which will eventually form phosphoric acid. No evidence exists to support bioaccumulation.

When transported as a cargo, aluminium phosphide belongs to the IMDG Code Class 4.3 and must be labelled as "dangerous when wet". Yet it should also be noted that aluminium phosphide pesticides are Class 6.1 and must be labelled as "toxic", yet most pesticides formulations contain at least 50% AlP and the hazard of a water reactive cargo still remains.

By the early evening of July 27, specialized response units were at the scene or en route. The vessel was evacuated with the exception of the captain and crew who still refused to leave. A series of "Hot" "Decon" and "Safe" zones had been established along with the appropriate security measures. Due to the substantial threat to the port and public, the response was designated a federal action under the National Contingency Plan.


By late morning of July 28, the following actions had been undertaken:

1. Technical information had been assembled and disseminated to the various agencies.

2. Traps were put in place to cover the open hold since rain and high humidity could potentially further activate the damaged cargo.

3. Detection equipment (colourimetric Indicator tubes and a photoionization detector) were field-tested with reacting Gastoxin and phosphine gas of known concentration. (The colourimetric indicator tubes were found not to be sufficiently accurate above 50ppm.)

4. A supply of indicator tubes were obtained to monitor phosphine at 50 to 100ppm concentration levels.

5. Initial inquiries were made to locate an appropriate disposal site.

By late morning of July 29, the master and crew were forcibly removed from the vessel and the following course of action taken:

1. The daily work schedule was set to maximize the use of cool morning hours. Work was suspended when the temperature in the hold approached 38ºC.

2. Liquid nitrogen was used to cool the hold and cargo after personnel had evacuated the ship.

3. Flasks were overpacked in recovery drums to organize and aid future handling. Powdered lime was added as a packing buffer and desiccant material within the overpacking. Lids were left loose on the drums to avoid accumulation of gas and further explosion.

4. Constant air sampling was conducted and readings were constant in the 10 - 40ppm range indicating that a reaction was underway. An inadvertently sealed drum contained 300ppm in its head space and gas was observed to "burp" from the lime in numerous drums.

5. The vessel owners and importer made repeated attempts to reclaim the cargo for transport by container truck even though there was evidence that a reaction was in progress in the flasks.

Disposal options were then considered as follows:

1. Landfilling at an approved waste site; flasks would be packed in drums filled with lime to be buried in trenches with clay and plastic liners. Any escaping phosphine gas would slowly percolate through the soil to be rendered inert by soil chemistry or emerge at concentrations well below threshold values. However, each potential site was eliminated due to public safety and health concerns.

2. High temperature combustion; although possibly very effective, the explosive nature of the material did not make this a viable option.

3. Exposing the substance for a controlled air reaction so that gas could disperse harmlessly and the resulting residual ash would be non-hazardous and could be left on-site; since this method would have involved transporting the material long distances over public routes near population centres with much handling of the cargo, it was not considered a safe option.

4. Using modern incendiary explosives such as those used in demolition work; this would consume the product in the same manner as a rotary kiln but without the risk described in option 2; as in option 3, due to the requirement of transport to remote areas through populated routes, it was not considered a safe option.

5. Repackaging and stabilizing the product for shipment; since the product was undergoing an uncontrolled reaction producing high levels of phosphine gas, this option was dismissed.

6. Ocean dumping, which although was the leas popular since it would require a vessel, specialized equipment, potential of exposure of response personnel during the operation and possible environmental effects, it had the advantage that the product be removed from populated areas and that the disposal would be final.

The request for an ocean dumping permit addressed:

1. Selection of an appropriate site.

2. Fate of the product in the marine environment.

3. Environmental impact associated with ocean dumping to commercial and endangered species.

4. Details to ensure that the cargo would not leave the disposal site at a later date.

5. Safety of response personnel during the operation.

The ocean disposal site selected was one which previously had been used for disposal of biological sludge from an industrial waste water treatment system and measured an area of 26km by 30km. The proposed dump site was located over a portion of the sea floor continental slope. Biologically, this environment is of low diversity and biomass. No commercially or recreationally sought species of fish or shellfish are found at the bottom of the dump area. Other species found in this area were common, widely distributed, seasonal and recolonize frequently. The mid-depth and surface waters are used by the pelagic species of tuna, swordfish and cetaceans common to the Gulf waters of the U.S.A. but not frequently or exclusively.

The most serious environmental effect was the depletion of oxygen. Once the aluminium phosphide reacted with sea water to form phosphine, the gas would dissolve in sea water to react with dissolved oxygen to form phosphoric acid which in turn would disassociate into dissolved salts of sodium and magnesium biphosphate. Thus it was predicted that there would be a short-term depletion of dissolved water as phosphine converted to phosphoric acid. However, this was not considered to be biologically significant given the large mass of dissolved oxygen in the water.

On August 3, the dumping permit was granted and an offshore supply vessel was leased to carry the drums of Gastoxin which had been placed in containers. A Coast Guard vessel accompanied the supply vessel. A trial using inert material was performed to test if the flasks would sink since it was feared that empty flasks would refloat and be washed ashore creating alarm if anyone found flasks with hazardous labels being washed ashore.

All commercial traffic was excluded from the dumping zone and personnel equipped with protective equipment began the ocean dumping procedure. Each of the 7000 flasks was manually punctured several times with a horn of a fire axe before releasing the flask overboard. This was done to ensure that the flasks were negatively buoyant.

An analysis of the way the accident was handled was carried out. A wrong choice was made in the selection of one of the monitoring equipment since although intended for explosive atmospheres, it was intended to detect explosive atmospheres of hydrocarbon products and not phosphine. The use of lime as a packing agent was unwise since it gave tremendous dust problems and did not serve the intended purpose. Ocean dumping was shown to be a safe and satisfactory option that could be recommended for aluminium phosphide and other similar chemicals which produce toxic and flammable hydrides such as arsine, diborane, germane, silane and stibine.