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12137 Chemical accident in Canada with hydrogen (gas)
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General accident information
Class/Quality * * * *
Year 1994
Summary Due to low concentration of h2
A tank of 35/M3 exploded
Country CDN
Chemicals Chlorine, Chlorine, Hydrochloric acid, Hydrochloric acid,
Hydrochloric acid, Hydrogen (gas), Hydrogen (gas), Hydrogen (gas),
Hydrogen (gas), Hydrogen chloride, Hydrogen chloride
Cause Op/Others-ext/Fail
Fatalities/Injuries 0 / 1
Occurrences or events Blow-away, Burn, Burst/Rupture, Chemical reaction,
Clog, Cooling, Damage, Defective-working,
Explosion, Fire fighting/Emergency response, Ignition, Insufficient ventilation,
Mix, Overpressure, Penetrate/Puncture, Pollution/Contamination,
Pollution/Contamination, Pollution/Contamination, Pump-over, Pump-over,
Release, Static-electricity, Wrong-action, Wrong-composition,
Wrong-composition, Wrong-composition, Wrong-composition
Full accident information 
download accident report Click here to view a document containing the full accident information

Country: CDN
Date : 1994 1102

A contractor, who delivered hydrogen gas to a chemical factory, did not
advise about the low concentration of hydrogen. The minimum hydrogen
concentration should be 98 instead of 80%. The operator of the chemical
factory had no indicator of the hydrogen quality at the control station, so
he did not know that the hydrogen concentration (80%) was below the
criteria (>98%).

The process was described as follows.
Chlorine gas burns in a combustion chamber (synthesis 1) with hydrogen gas
(concentration >98%) to produce hydrogen chloride gas. The hot hydrogen
chloride gas goes through a cooling absorbing system (synthesis 2) and
another absorbing system (synthesis 4). In the absorbing system (synthesis
4) low acid of tank nr. 1 and water separately has been added. After this
the hydrogen chloride liquid has been carried back to absorbing unit
(synthesis nr.2). Together with some hydrogen gas, which normally
penetrated through a seal joint, the generated hydrochloric acid, with a
concentration between 32-36% has been stored in tank nr. 2.

What went wrong.
Tank nr 1, which contained low acid (concentration 0-22%), had no
filtration of acid entering in tank nr. 1. So residues present at the
bottom of the tank were probably carried by the low acid pump to the
adsorbing unit (synthesis 4). The low acid flow became too low at the
adsorbing unit (synthesis 4) and the inflow of low acid to absorbing unit
(synthesis 4) stopped.
The seal joint, which was not conceived to resist such a pressure, damaged
(broke). An important quantity of chlorine gas went through the seal joint
and also an important quantity hydrogen gas possibly went through the seal
The design criteria of the tank nr. 2 ventilation system were established
to evacuate soluble hydrogen contained in the hydrogen chloride. In tank
nr. 2, contents 35/m3, hydrochloric acid (concentration 32-36%) had been
The ventilation system of tank nr. 2 did not eliminate the entering
explosive mixture of hydrogen/chlorine.
Possibly static electricity generated by the flow of liquid hydrochloric
acid in tank nr. 2 ignited the explosive mixture. A violent explosion
occurred and tank nr. 2, filled with hydrochloric acid, ruptured. The top
of the tank was thrown 200/meters and manhole was ruptured. 38/m3
hydrochloric acid spilled out as liquid and a worker was bothered by
hydrogen chloride fumes. The ground had been polluted with liquid and the
production interrupted 6/days.
Material damage of 1.8E+6 USA dollars.

Lessons learned (preventive measures taken):

1. Hydrogen quality meter installed at the DCS.
2. Ventilation system of tank with nitrogen (purging) flow was installed.
3. Operation procedure was reviewed.

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