At around 8:20 p.m., a runaway reaction occurred with the release of ammonia in the sifting/granulation workshop of a pharmaceutical manufacturing plant. At the time of the accident, a calibration operation was being performed on a 500-litre stainless steel tank containing hydroxycarbamide (hydroxyurea) and silicium dioxide. White smoke, followed by black smoke billowed from the workshop via the tank’s vent following the removal of the filtration unit. A technician shut down the equipment and covered the vent with a bag to limit the release.

A smoke detector was triggered, resulting in the automatic shutdown of the workshop; the building was evacuated. The emergency services measured an ammonia concentration in the building of more than 600 ppm (measuring tubes saturated). They were able to neutralise the releases using water curtains placed on the roof and water was injected into the 500-litre tank. The intervention was completed the next at 5 a.m.

Consequences and actions taken

Two firefighters sustained chemical burns during the intervention and three employees, intoxicated by the smoke, were taken to the hospital. Other employees exposed to the fumes received a medical examination at the site.

The water used to neutralise the ammonia (80 m³) entered the rainwater network.

The 500-litre tank containing the residual product was processed by a specialised company.

Production operations were stopped for more than a week. Manufacturing operations using hydroxycarbamide were suspended in all of the site’s production facilities. The resumption of operations is conditional on the results of a technical study integrating the accident feedback and the adoption of measures to avoid the recurrence of such an event.

Causal analysis

The operator conducted a study on the chemical reactivity of hydroxycarbamide to determine the cause of the accident. Considering the facts observed (release of ammonia and an increase in the tank’s temperature), the assumptions are as follows:

• hydrolysis of hydroxycarbamide. In the presence of water, hydroxycarbamide forms carbon dioxide, hydroxylamine and ammonia. Water may have come from the detergent used to clean the tank;
• thermal degradation of hydroxycarbamide. This unstable compound decomposes when exposed to heat, forming ammonia, carbon dioxide and isocyanic acid. On the day of the accident, the stainless steel tank containing the product had been left out in the sun the entire afternoon.

The risk of decomposition, starting at 50 °C, is indicated in its material safety data sheet (MSDS). The temperature reached during the decomposition reaction is unknown because the tank was not equipped with a temperature measuring device.

Furthermore, the Classified Facilities Inspection Authorities noted several anomalies:

• the MSDS was out of date;
• the sprinkler system was not triggered;
• the building concerned was not connected to the containment basin;
• no shut-off valve on the rainwater network.

Measures taken

Facility operator proceeded to:

• the inspection of the sifter by a certified body;
• the review of the cleaning procedure for mobile equipment and components in the manufacturing sectors (drying of the 500-litre tanks and calibrators using disposable cloths and compressed air, record of cleaning operations and inspection of these operations);
• application of solar protection films to the workshop’s windows to avoid heating of the tanks;
• updating of the internal emergency plan;
• updating of the unique risk evaluation document;
• study of the installation of sectional valves on the site’s rainwater network (which recovered the water used to neutralise the ammonia fumes).