On March 4, 2005, Employee #1 (leadman) was performing a
hydrostatic pressure test on a large stainless steel pressure vessel at a plant
which manufactures pressure vessels. The tank was cylindrical, about 14 in.
diameter and 24 in. long. The tank was pressurized to 150 psi for the test.
Upon successful completion of the test, he was draining the water from the
tank. He soon discovered that the water would not drain very quickly, as the
internal configuration of the tank was such that a vacuum was being created here
were inadequate air openings to displace the draining water. After consultation
with the plant supervisor and plant manager, it was decided that compressed air
would be pumped into the tank to force the water out for a short time, then
more openings would be exposed and the water could drain by itself. 110
psi air was pumped into the tank by Employee #1 and supervisor, and the
water began draining. The supervisor turned the job back to Employee #1.
Sometime later, the air hose was disconnected, and the compressed air was also
allowed to bleed off. About an hour after the draining began, Employee #1
ordered another coworker to close the drain valve. Employee #1 then went to the
area of the drain valve and is presumed to have begun to remove the quick-closure
clamps used to seal a tank portal several inches higher than the drain.
Normally, the water would be pumped from an opening near, but above the drain
when the water levels had dropped to near the drain level. This employee
apparently had seen air bubbling out in the drain line and assumed (correctly)
that the water level had dropped to near the drain level.
The air pressure,
however, had not completely off, and when the clamp was loosened, it flew off
at him accompanied by a massive air pressure release. Employee #1 received head
and neck injuries when being struck by the blanking plate and when his head was
snapped back from the release. Employee #1 was paralyzed in the hospital for
several days before he died of respiratory and other complications. The
employee and the supervisor were very experienced at hydrostatic pressure
testing, but pneumatic pressure testing was extremely rare at the plant. They
had never had to pump in air to drain a tank before. The company had procedures
for both hydrostatic and pneumatic tests, and each employee was trained several
years earlier on these procedures. Several days earlier, an attempt to fill the
tank with water for the test was unsuccessful, as the same lack of tank
openings near the top of the tank would not allow for this to be filled. An
extra hole was drilled to allow for filling. Quick-closure clamps are very
rarely used during these tests, but the type of clamp used for the test is
dependent on the type of clamp that will be used once the tank is put into
production. A witness said that the employee was hurried during the draining
process. It was Friday, and the tank needed to be shipped on Monday, and there
was more work to be done on the tank. He was also working on another tank
nearby. The tank had two pressure gauges mounted at the high point of the tank,
these both should have read water and air pressure as well. Both were working
before and after the test. The gauges were on the same line as was used to
force compressed air into the tank. To read these gauges, the worker would have
to walk to the end of the tank away from the drain and climb up a
shortstepladder. There was no procedure or training for doing the work in this
particular manner. How long to pump in the air, what steps were needed to ensure
that the pressure was dissipated, what measures were needed to avoid
reintroduction of pressure or how safely release the pressure was not
specified? The normal hydrostatic test calls for the employee to make sure that
the pressure is at zero before opening the tank. In a normal hydrostatic test,
the tank pressure would drop to zero very shortly after the tank draining
began.
Source: Osha.gov
