Narrator: On August 19, 2004, an explosion at the
Sterigenics International Facility in Ontario, California injured four workers and caused extensive
damage to the 66,000 square foot facility. The blast occurred when ethylene oxide gas, used
in the sterilization process, ignited and exploded. The U.S. Chemical Safety and Hazard
Investigation Board investigated the accident. Bresland: This was an incident involving a chemical
that is both highly flammable and toxic to humans. It is fortunate that no one was in
the immediate vicinity of the explosion, because it was likely there would have been
more serious injuries and possibly fatalities. McClure: The CSB investigation revealed several
factors that led to the explosion at Sterigenics. This video digest is intended
to graphically show what happened and how such accidents may
be prevented in the future. Narrator: Sterigenics International uses
ethylene oxide to sterilize medical products such as syringes, catheters and bandages
and then ships them to medical suppliers. Products arrive at the plant prepackaged and stacked on
pallets, ready to be sterilized in large steel chambers. The plant contains eight
sterilization chambers, operated and monitored by personnel
using a computer system in the control room. Packaged medical products are added to
the chamber and the doors are sealed. The chamber is then
filled with ethylene oxide, which penetrates the packaging
over a period of several hours, killing any germs and
sterilizing the products inside. After the sterilization phase,
ethylene oxide is removed from the chamber and the packaged products
in several steps. First, about half the gas is pumped from the chamber
to a pollution control device called a scrubber, where it is removed by chemicals. Next, virtually all of the remaining ethylene oxide
is removed in a step called "gas washing." This involves injecting air and nitrogen into the chamber,
where they mix with the ethylene oxide. This mixture is then pumped
from the chamber to the scrubber. This process is critical to reducing the
concentration of ethylene oxide to below explosive levels and is repeated several times, until there is
only a trace amount of ethylene oxide remaining. This trace amount of
gas is not explosive, but it is toxic and must be removed by
ventilating the chamber before workers can enter. The front door is raised a few inches, which
automatically opens a vent at the rear of the chamber. Air is drawn through the chamber to another
pollution control device called a "catalytic oxidizer." Once the air enters the catalytic oxidizer,
it is heated as it passes over open flames. Any remaining traces of ethylene oxide are
removed as the air passes over a metal catalyst. After the chamber has been ventilated for several
minutes, operators can safely enter to remove the products. McClure: During the sterilization process, gas washes are key to removing
ethylene oxide and preventing explosions. But on the day of the accident,
this critical step was bypassed. Narrator: On August 19, 2004, the
computer alerted operators to a possible error in the amount of ethylene oxide that
had been injected into Chamber Number 7. Operators in the control room instructed the computer
to abort the sterilization cycle and remove the gas. The system automatically
performed the normal series of gas washes, which removed virtually
all of the ethylene oxide. Finally, the chamber was
ventilated to the oxidizer. Operators then removed the
products from the chamber. Maintenance technicians arrived and
performed tests, which did not reveal any problems. They then ran a test cycle that injected 120
pounds of ethylene oxide into the empty chamber. And again, they could
not identify a problem. As the system performed the first step
of pumping ethylene oxide to the scrubber, the technicians asked the supervisor for
permission to bypass the time-consuming gas washes. The supervisor agreed. All of them incorrectly believed that because there
were no products in the chamber to absorb ethylene oxide, all the gas would be removed in the first step,
making the gas washes unnecessary. They did not realize that about half of the ethylene
oxide originally injected still remained in the chamber. There was no monitoring system to alert
them to this explosive concentration of gas. The supervisor provided a technician with his
special computer password to manually advance the cycle, bypassing the gas washes. A short time later, the front door was raised,
activating the chamber ventilation system. This drew a large amount of
ethylene oxide from the chamber, through the back vent, to the
open flames in the oxidizer. The explosive gas ignited. A flame front traveled back through the ducting,
into the sterilization chamber, igniting the remaining ethylene oxide
and causing a powerful explosion. It destroyed the sterilization chamber, bulging the chamber walls outward,
blowing off both of the two-ton chamber doors, sending one of them 75 feet away,
knocking out this hole in the north wall. The force of the blast caused widespread
structural damage throughout the building. The control room was showered
with flying glass from the windows. Debris, including the computers that control
the process, littered the inside of the room. McClure: While the accident would seem to have been
caused by a single event, bypassing the gas washes, the CSB investigation actually
revealed several causes for the explosion. Narrator: The supervisor with the critical password
did not understand why the gas washes were essential, whether the chamber was
empty of products or not. Next, the sterilization chamber was
not equipped with a gas monitoring system to warn employees of
explosive levels of ethylene oxide. And the company's process hazard analysis program
never thoroughly evaluated the hazard presented by the oxidizer, despite a history of
oxidizer explosions in the sterilization industry. Narrator: The CSB investigation noted that the control
room had glass windows that were not shatter-resistant. The control room suffered
significant damage in the explosion and all the injuries
occurred to workers inside the room. Selk: If your control facility is located
in an area where an explosion could occur, consider using reinforced window materials
or replacing any windows with video cameras. Another lesson from this incident is
the importance of regular training. Maintenance technicians had last been
trained about the need for the gas washes in 1997, seven years before the incident. The maintenance supervisor, who was
authorized to use a password to skip the gas washes, was hired after 1997 and
never received the training. Selk: So a very important
lesson is, be sure personnel are fully trained on process hazards before
authorizing them to override automatic systems. Narrator: The CSB made several recommendations
to the company, government agencies and others. Bresland: Oxidizers are commonly
used for reducing air pollution. However, they have been the
source of numerous explosions. Our recommendations are
aimed at reducing this hazard. Inside an oxidizer, fuel, air and
an ignition source are all present. There is a serious risk if the
fuel/air mixture is too concentrated. Facilities with oxidizers should
use multiple layers of protection, such as gas monitors, safety interlocks and alarms, to
prevent a single mistake from leading to an explosion. Bresland: The CSB recommended that the
National Fire Protection Association, which creates fire codes
used around the country, require additional safeguards to prevent
explosions at ethylene oxide facilities. Specifically, we recommended the
codes require the use of gas concentration monitoring equipment, alarms and
explosion damage control devices. We also recommended that
Sterigenics install similar safety devices and improve its employee
training and hazard analysis programs. Finally, we recommended that the National
Institute for Occupational Safety and Health or NIOSH work with the ethylene oxide industry to promote
the use of gas monitoring and other safety measures. Bresland: CSB recommendations
are aimed at preventing accidents. If followed, we believe these recommendations will
go a long way towards developing safer workplaces. Bresland: To read the full report on the
CBS's investigation, visit our website at CSB.gov. Thank you for watching
this CSB Safety Video.
