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11050 Chemical accident in Senegal with ammonia anhydrous
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General accident information
Class/Quality * * * * *
Year 1992
Summary Physical explosion of parked road tanker carrying
Ammonia caused major accident due to overfilling
And 1279 casualties
Country SN
Activity USE/APPLICATION
Location FACTORY
Chemicals Ammonia anhydrous
Cause Human-failure
Fatalities/Injuries 129 / 1150
Occurrences or events Blow-away, Crack, Dismount/Disconnect, Drive,
Evacuation, Fill, Fire fighting/Emergency response, Fire fighting/Emergency response,
Overfill/Overload, Overfill/Overload, Overheating, Overpressure,
Physical-explosion, Pollution/Contamination, Release, Traffic-interruption,
Welding/Cutting, Wrong-action
 
 
Full accident information 
download accident report Click here to view a document containing the full accident information

Country: SENEGAL (SN)
Date : 1992 0324


The oilseed processing facility involved in the accident is owned by one of the largest companies in Senegal, which has the monopoly on the seed cake and peanut oil market.
The unit in question was located in the industrial sector of the harbour zone. The unit performed the detoxication of peanut cakes (through the elimination of aflatoxin) by a hexane extraction process which also uses formaldehyde and ammonia.
The ammonia is imported by boat by a fertilizer manufacturing company which is also located in the harbour. The latter stores the ammonia required for its manufacturing process in three 3E+6/kg spheres, that are refrigerated to a temperature between -5 and -2/C. Part of the ammonia is sold to the food processing plant which sends its tanker trucks to the fertiliser plant's storage installations.
During the processing of oil from peanuts ammonia was used to detoxify the product. The ammonia was stored in a tank on a semi trailer. The specifications of the tank were:
contents : 33.5/m3
diameter of the tank : 2.2/m
thickness of the wall : 11/mm
material : anneal hardened steal
year of construction : 1983
year of last maintenance : 1991.
In the period from 1983 till 1991 the tank was frequently overfilled. Due to the overfilling a little crack was detected and repaired. The crack was welded and the weld did not get an annealing treatment. After this the tank was again frequently overfilled. Some time before the accident the tank was filled with 22180/kg liquid ammonia and the tank was placed on the factory yard.
The environmental circumstances during the accident were:
temperature : 25.7/C
winddirection: north
windspeed : 4/m/s

The eve of the accident, the tank in question was loaded at 1600 hours from a storage unit belonging to the fertiliser plant, then transported to the seed cake treatment plant and placed near the detoxication unit's unloading station. It was not connected as an identical tank was already being unloaded. The detoxication unit is not equipped with a storage unit specifically for ammonia; it is supplied directly from the transport tanks. The next day at 1330 hours, the tank suddenly burst open along the central shell which rolled out completely flat.
The front and rear of the tank, while only very slight deformed, were propelled by the force of the reaction.
In a more or less horizontal trajectory, the front of the tank clipped part of the installations then smashed into the wall of an electrical service building. The trajectory of the rear of the tank is more difficult to establish.
Based on the findings, it appears that it was propelled upward at approximately a 45?? angle. After colliding violently with a massive reinforced concrete lintel, it ricocheted toward the detoxication installation, causing significant damage to the unit's upper levels.
The force of the first impact caused the running gear to separate from the tanker chassis. The axle was found in a neighbouring street roughly fifteen metres away and the second axle was thrown 200/m into a neighbouring establishment.
Part of the ammonia contained in the tank (22E+3/kg) spread into the installation. Another part, carried along with the back of the tank, was thrown outside the establishment (according to the doctors, numerous bodies found in this sector had received burns through direct contact with the liquefied ammonia).

The consequences
A month after the accident, 116 deaths and 1,150 injured were declared; in all, the accident claimed 129 lives. The medical teams which followed up on the victims observed, as with chlorine intoxication, that individuals with seemingly minor lesions developed a fatal pulmonary oedema in the days following the accident.
Due to the normal weather conditions the tank was heated up. The internal pressure increased and due to a physical explosion, the tank was blown away in 2 parts. Several buildings and units were damaged. A part of the tank damaged the control room of the factory.
There were 129 fatalities and 1150 injuries. Due to the inhalation of the ammonia vapours the woundings were respiratory lesions and lung edema.
The fire brigade had no masks enough, so rescue attempts were seriously hampered by a lack of breathing equipment and several firemen collapsed after inhaling caustic ammonia gas. They were assisted by the army and the French navy.
Due to the Ramadan and the holiday of nearby schools the amount of fatalities and injuries was fortunately not higher.
The information collected allowed a few elements to be established relevant to the risk analysis:
1.
Liquid ammonia was projected up to 30/m. These projections could have been greater if the back of the tank had not been stopped by the building.
2.
The whitish cloud, most likely be attributed to the aerosol, spread very rapidly and developed upward. According to witnesses, the cloud moved 250/m then was "relatively rapidly reabsorbed" (within 10 to 15/min.). The description of the ammonia aerosols, observed during other accidents as being very dense and well-defined, does not correspond exactly to the testimonies gathered. The cloud was described as turbulent and allowing someone to stay in it over a distance of ten or so meters with only a handkerchief as protection. Nevertheless, the unbreathable atmosphere prevented the rescue services from intervening owing to a lack of sufficient protective equipment (masks, oxygen cylinders...).
3.
The majority of the people killed in the moments following the explosion were in the semi-confined areas of the establishment (installation, streets, and rooms where the windows had been blown out...), or in the port's restaurant sector located nearby. A plant manager who was blocked in his office for 25 minutes (as the door was jammed due to the blast from the explosion) was not injured.
4.
The "cloud" was practically reabsorbed in 15/minutes in and along the establishments streets near the site of the accident, despite the liquid NH3 leak caused by the ruptured hoses of the neighbouring tank that was being unloaded, and which was stopped only a half hour after the explosion. After a half-hour, the French military who were providing assistance to the Senegalese authorities, entered the establishment's courtyard without masks approximately 100/m from the accident location.
5.
There was no fire.
Despite the special meteorological characteristics at the time of the accident (temperature 28/C, high humidity, low winds with unstable direction), it appears that the risk zones were short of the forecasts given by the habitual models.
The victims were between 3 months and 74-years-old. Among the 91 dead there were 15 women and 76 of the male sex. The recent lesions were discovered in the subjects who died during the first three days. The consisted of some extended cutaneomucous burns, a sharp lung oedema sometimes associated with a pulmonary emphysema. Later on, results show that deaths are rather caused by the after effects of a pneumopathy (pulmonary infection, bronchiectasis, pulmonary fibrosis). Ammonia belong to the irritating and caustic gas. The intensity of the lesions and the mortal risk are proportional to the quantity of gas per m3 of air. If the lesions described in our research have similarities with the published description, the latter mentions only a few cases of death. The originality of our series is particularly found in the intensity of the lesions and the number of deaths. This shows the insufficiency of both means of prevention and emergency assistance.

Cause
The tank was built in 1983 by a French company. Its construction was monitored by the French administration and was certified in compliance with French regulations relative to the transport of dangerous materials. However, it had been repaired in 1991 after a leak was discovered during hydraulic testing. According to the findings, it appears that the tank ruptured in the location where the repair had been made.
The inquiry conducted by the Senegalese authorities established that the tank that ruptured had been overfilled several times. The day before the explosion, it was loaded with 22.18E+3/kg of ammonia instead of the 17.685E+3/kg authorised by the tank's original specifications and the maximum filling level established by land transport regulations (TDG - 0.95).
Furthermore, this load corresponds to an ammonia volume of 34.37/m3, more than 1/m3 of the tank's original volume.
This confirms the previous deformations of the tank associated with the overfillings.
The time (1.30 ??? shift change) and location of the accident (near the industrial port's restaurant sector) are aggravating factors which partly explain the serious consequences of the accident. According to the press, certain individuals who came to investigate the source of the explosion were also among the victims.

In the emotional climate that inevitably follows a catastrophe of this magnitude, the local representatives of the International Labour Office (ILO) and a French mission of the Classified Installations Inspectorate were able to reach the site rapidly. The very lax attitude of the Senegalese governmental authorities and the management of the establishment concerned should be noted.

Ammonia-gas poisoning: respiratory troubles evaluated by functional exploration
The objective of research is first to evaluate the defects in the respiratory function which have been noticed among patients suffering from ammonia poisoning during the accident. Secondly it is to set precisely the seriousness of the problem. This retrospective study is carried out on 50 patients examined at the Physiology and Functional Exploration Laboratory of the faculty of Medicine of Dakar University from March 1993 to October 1995. These patients have been submitted to at least two respiratory functional explorations. Ten of them have been treated for two years, thus benefiting from a spirographic control of these respiratory troubles already noticed. 58% of the patients have developed an obstruction syndrome with the following specifities: fourteen patients out of 29 revealed a serious stoppage of the bronchi, twelve had a moderate bronchial obstruction, and three showed a minor bronchial obstruction. Besides, 34% of the patients have developed a mixed syndrome with a minor restrictive component and a severe obstructive component. 8% of the poisoned have presented a normal lung function testing. About the localisation of the respiration disorders at the level of the bronchial system, 61% of the patients have shown an obstruction of the proximal, medial and distal bronchi. 26 % have presented obstruction of the distal bronchi, 13% have shown an attack at their medial and distal bronchi. 5 patients out of 10 have shown any modification in their respiratory troubles while 3 of 10 have shown significant improvement. Then 2 out of 10 have shown degradation in their respiratory problems with an extension of bronchial obstruction. The ammonia poisoning has caused serious respiratory disorders related to the general and local toxic action of ammonia on the respiratory tract, its retention at their level and its effects on the respiratory function. The severity of the patent injuries incites to issue recommendations concerning the prevention of ammonia poisoning and the quick and efficient taking charge of the casualties in case of any accidental intoxication.

Lessons learned
Following the accident, the establishment's procurement procedures underwent extensive modifications:
The ammonia is imported from Europe in 12.5-tonne containers and the maximum storage quantities at a site are:
- one container at the oilseed detoxication facility,
- a dozen containers in a storage area on property near the plant.
This new storage method offers significant greater security, owing to:
- unitary capacity less than that of the former tanks (18E+3/kg),
- filling is performed by the production plant with respect to a load limit,
- protection by rupture disk and valve,
- bottom closure valves upstream from the shut-off valves, capable of being operated remotely by cable.


L'??tablissement qui traite des ol??agineux, est la propri??t?? de l'une des soci??t??s les plus importantes du S??n??gal, qui dispose du monopole de la commercialisation des tourteaux et des huiles d'arachide.
L'unit?? accident??e est implant??e dans le secteur industriel du port. Elle permet la d??toxication des tourteaux d'arachide (??limination de l'aflatoxine) par un proc??d?? d'extraction ?? l'hexane utilisant Sous l'effet du premier choc le train roulant se d??solidarise du ch??ssis de la citerne. Un essieu est retrouv?? dans la rue voisine ?? une quinzaine de m??tres et le second essieu est projet?? ?? deux cents m??tres dans un ??tablissement voisin.
Une partie de l'ammoniac contenu dans la citerne (22,18 t) se r??pand dans l'installation. Une autre, entra??n??e avec l'arri??re de la citerne, est projet??e hors de l'??tablissement (de nombreux corps retrouv??s dans ce secteur portaient, selon les m??decins, des traces de br??lures dues au contact direct avec l'ammoniac liqu??fi??).??galement du formol et de l'ammoniac.
L'ammoniac est import?? par bateaux par une soci??t?? de production d'engrais ??galement implant??e sur le port.
Cette derni??re stocke l'ammoniac n??cessaire ?? ses fabrications dans trois sph??res de 3000 t chacune, r??frig??r??es ?? une temp??rature comprise entre -5 et -2??C. Une part de l'ammoniac est vendue ?? l'usine d'agroalimentaire qui vient s'approvisionner par camion citerne aux installations de stockage de l???usine d???engrais.

La veille de l'accident, la citerne en cause avait ??t?? charg??e ?? 16 h ?? partir du stockage de l???usine d???engrais, puis conduite ?? l'usine de traitement de tourteaux et mise en place au niveau du poste de d??potage de l'unit?? de d??toxication.
Elle n'avait pas ??t?? raccord??e, une citerne identique ??tant d??j?? en d??chargement. L'unit?? de d??toxication qui ne dispose pas de stockage propre d'ammoniac, est aliment??e directement ?? partir des citernes de transport.
Le lendemain ?? 13h30 la citerne s'ouvre brutalement au niveau d'une virole centrale qui se d??roule compl??tement ?? plat. L'avant et l'arri??re de la citerne, peu d??form??s, sont propuls??s par r??action.
Dans une trajectoire vraisemblablement horizontale, l'avant de la citerne "fauche" une partie des installations puis d??fonce le mur d'un local ??lectrique. La trajectoire de l'arri??re de la citerne est plus difficile ?? ??tablir.
Compte tenu des constatations effectu??es, il est semble-t-il propuls?? vers le haut avec un angle d'environ 45??. Apr??s avoir heurt?? avec violence un important linteau en b??ton arm?? du b??timent voisin, il ricoche en direction de l'installation de d??toxication et provoque les importants d??g??ts constat??s dans les niveaux sup??rieurs de l'unit??.
Sous l'effet du premier choc le train roulant se d??solidarise du ch??ssis de la citerne. Un essieu est retrouv?? dans la rue voisine ?? une quinzaine de m??tres et le second essieu est projet?? ?? deux cents m??tres dans un ??tablissement voisin.
Une partie de l'ammoniac contenu dans la citerne (22,18 t) se r??pand dans l'installation. Une autre, entra??n??e avec l'arri??re de la citerne, est projet??e hors de l'??tablissement (de nombreux corps retrouv??s dans ce secteur portaient, selon les m??decins, des traces de br??lures dues au contact direct avec l'ammoniac liqu??fi??).

Les cons??quences
Le bilan de cet accident apr??s un mois est de 116 morts et de 1150 bless??s; 129 morts seront finalement ?? d??plorer.
Les ??quipes qui ont assur?? le suivi m??dical des victimes ont observ??, comme pour les intoxications par le chlore, que des personnes atteintes de l??sions jug??es sans gravit?? dans un premier temps, d??veloppaient un oed??me pulmonaire fatal apr??s quelques jours.
Les informations recueillies permettent d'??tablir quelques ??l??ments utiles ?? l'??valuation des risques:
1.
Des projections d'ammoniac liquide ont atteint une trentaine de m??tres. Elles auraient probablement ??t?? beaucoup plus importantes ?? l'ext??rieur de l'??tablissement si l'envol de l'arri??re de la citerne n'avait ??t?? arr??t?? par un b??timent.
2.
L'expansion d'un nuage blanch??tre que l'on peut attribuer ?? l'a??rosol, a ??t?? tr??s rapide, et s'est d??velopp??e vers le haut. Le nuage s'est d??plac?? sur 250 m puis, selon les t??moins, s'est "assez rapidement r??sorb??" (10 ?? 15 min). La description des a??rosols d'ammoniac, faite ?? l'occasion d'autres accidents, tr??s denses et bien d??limit??s ne correspond pas exactement aux t??moignages recueillis ici. Le nuage est d??crit comme turbulent et permettant un s??jour court sur une dizaine de m??tres de profondeur avec un mouchoir comme seule protection. N??anmoins, l'atmosph??re irrespirable a g??n?? l'intervention des secours qui ne disposaient pas d'??quipements de protection suffisants (masques, bouteilles d'oxyg??ne...).
3.
La plus grande partie des personnes tu??es dans les premiers instants l'ont ??t?? dans les zones semi-confin??es de l'??tablissement (installation, rues, locaux dont les vitres avaient ??t?? bris??es...), ou dans le secteur des restaurants du port situ??s ?? proximit??. Un responsable de l'usine qui s'est trouv?? enferm?? 25 min dans son bureau (porte coinc??e par le souffle de l'explosion) n'a pas ??t?? bless??.
4.
Le "nuage" s'est pratiquement r??sorb?? en un quart d'heure, au niveau des ruelles de l'??tablissement proches du lieu du sinistre, malgr?? la fuite de NH3 liquide due ?? la rupture des flexibles de la citerne voisine qui ??tait en d??chargement, et qui n'a ??t?? arr??t??e qu'une heure environ apr??s l'explosion. Apr??s une demi-heure, les militaires fran??ais, qui apportaient leur appui aux autorit??s s??n??galaises, ont p??n??tr?? sans masque dans la cour de l'??tablissement ?? environ
100 m du lieu du sinistre.
5.
Aucun incendie ne s'est produit.
Malgr?? les particularit??s du contexte m??t??orologique de cet accident (temp??rature de 28??C, forte humi dit??, vents faibles et instables en direction), il semble que les zones de risques se situent en de???? des pr??visions donn??es par les mod??les habituels.

La citerne a ??t?? construite en 1983 par une soci??t?? fran??aise. Sa construction a fait l'objet d'une surveillance de la part de l'administration fran??aise et elle ??tait conforme au r??glement fran??ais de transport de mati??res dangereuses.
Cependant, elle avait ??t?? r??par??e en 1991 ?? la suite d???une fuite constat??e lors d'une ??preuve hydraulique. Selon les constatations effectu??es, il semble que la rupture de la citerne se soit amorc??e au niveau de cette r??paration.
L'enqu??te men??e par les autorit??s s??n??galaises a ??tabli que la citerne qui s'est rompue avait ??t?? l'objet de urremplissages ?? plusieurs reprises. Le 23 mars, elle avait ??t?? charg??e de 22,18 t d'ammoniac au lieu des 17,685 t permises compte tenu des sp??cifications d'origine de la citerne et du niveau maximum de remplissage fix?? par le TMD (0,95). Ce chargement correspond d'ailleurs ?? un volume d'ammoniac de 34,37 m3, sup??rieur de plus de 1 m3 au volume d'origine de la citerne. Ceci confirme les d??formations ant??rieures du r??servoir li??s aux sur-remplissages.
L'heure (13h30 - changement de quart) et le lieu de l'accident (?? proximit?? de la zone de restauration du port industriel) sont 2 facteurs aggravants qui expliquent en partie le lourd bilan. Selon la presse, des curieux alert??s par le bruit de l'explosion, et qui se seraient ru??s vers la zone accident??e, compteraient parmi les victimes.

Dans le climat passionnel, qui in??vitablement fait suite ?? une catastrophe de cette ampleur, la repr??sentation locale du Bureau International du Travail a particip?? ?? l'enqu??te et une mission fran??aise de l'Inspection des installations class??es a pu rapidement se rendre sur place. Il faut souligner l'attitude tr??s ouverte des Autorit??s gouvernementales s??n??galaises et de la Direction de l?????tablissement concern?? dans ce contexte.

Les enseignements tir??s
Suite ?? l'accident, les modalit??s d'approvisionnement en ammoniac de l'??tablissement ont profond??ment ??volu??:
L'ammoniac est import?? d'Europe en conteneurs de 12,5 t et les quantit??s maximales susceptibles d'??tre pr??sentes sont
de:
un conteneur au niveau de l'atelier de d??toxication des tourteaux,
- une douzaine de conteneurs sur une aire de stockage sur un terrain proche de l'usine.
Ce nouveau mode de stockage pr??sente un degr?? de s??curit?? substantiellement accru, du fait:
- d'une capacit?? unitaire inf??rieure ?? celle des anciennes citernes (18 t),
- d'un emplissage effectu?? par l'usine de production en respectant un taux limite de charge,
- d'une protection par disque de rupture et soupape,
- de clapets de fermeture de fond en amont des vannes de sectionnement, actionnables ?? distance par c??ble.



 
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