Page 24 - MGPI_Case_Study

Designing and installing automated systems for chemical unloading Other than a particulate filter, the fresh air intake that supplies
areas provides additional safeguards to unloading processes as the air to the control room does not include filtration or cleaning
systems automatically shut down valves supplying chemicals to bulk systems to effectively remove the chlorine gas or other gases from
or day tanks in the event of an unintended reaction or tank overflow. the outside air. Though shutting off ventilation systems during a
At MGPI, such an automatic shutoff device would have stopped the toxic release can the reduce impact on control room occupants,
flow of sulfuric acid that was reacting with the sodium hypochlorite the cloud had entered through the Mod B building intake before
in the bulk tank long before emergency responders closed the operators became aware of the release. MGPI had outdoor air
discharge valve on the Harcros truck nearly 45 minutes later. monitors near the Mod B tank farm to detect concentrations of

propylene oxide only. If the propylene oxide concentrations reached
5.3 MOD B VENTILATION a predefined set point, an alarm would sound in the control room

The CSB found that the pre-incident design of the Mod B and operators were required to shut down the ventilation system
building and ventilation system allowed for the intake of per the emergency action plan. The HVAC intake system had no
the cloud produced by the reaction, which forced operators toxic gas alarms that would have warned operators to don escape
to evacuate. Because the gases produced by the reaction respirators before the gases could enter through the vents.
overwhelmed the operators in the control room, they were forced

to evacuate and did not have time to retrieve their emergency In 2003 the CSB investigated a release of chlorine gas from the
escape respirators to protect them from respiratory hazards Honeywell International, Inc. (Honeywell) chemical plant in Baton
associated with even higher chemical concentrations outside. Rouge, Louisiana, which resulted in injuries to seven workers and
the issuance of a shelter-in-place advisory for residents within
85
The Mod B building has a positive pressure control room, a 0.5-mile radius. The chlorine was released from a failed
designed only to prevent harmful gases from the adjacent indoor coolant system and, as in the MGPI incident, entered an occupied
process area from entering the control room. Positive pressure is control room through the ventilation system. The CSB found
achieved by maintaining a higher air pressure in the control room that the Honeywell release lasted 3.5 hours, partly because
than in the indoor process area. MGPI’s heating, ventilation, and operators were forced to evacuate the area before they could

air conditioning (HVAC) system for Mod B has a 4-ton air handler diagnose the problem and isolate the source of the leak.
with a high-speed motor that draws air from two intakes located
on the exterior of the Mod B building. One of these intakes is As with MGPI, the Honeywell control room was positive pressure and
located on the first level of the structure, adjacent to the tank farm designed to prevent the infiltration of hazardous gases. However,
and bulk chemical transfer area. A gauge constantly reads and unlike the Mod B building at MGPI, which only maintained positive
compares the air pressure inside the control room to that in the pressure relative to the production area, the Honeywell control
production area. If the pressure in the control room drops below room was designed to maintain a higher pressure than the outside

that in the production area, an alarm alerts operators to evacuate. atmosphere. Because Honeywell attempted to prevent vapors from
outside entering the control room, the ventilation system intakes
Although MGPI designed the control room to protect were located at the highest point of the plant to pull in fresh air. The
occupants from harmful vapors inside the production area, CSB found, however, found that the positive pressure control system
design considerations did not include protecting occupants did not protect personnel or equipment during the 2003 release.
from harmful gases or vapors from outside the building. At Honeywell, the CSB observed holes and gaps in the HVAC intake
Because MGPI received and stored a number of hazardous ducts located on the roof, which allowed chlorine to be drawn into
chemicals in the chemical unloading area and tank farm, the building during the release. In addition, the Honeywell control
any vapors from tank trucks unloading or from any vents or

pressure release devices on the tanks could enter the control 85 CSB. Honeywell Chemical Incidents. August 8, 2005. http://www.csb.gov/
room through any doors, open crevices, or air intakes. investigations/completed-investigations/?F_InvestigationId=54 (accessed October 3,
2017).
24 CSB MGPI Processing Case Study