Human Engineering Factors Result in Increasing Number of Riser Disconnects

Effective Date: 5/31/2005

U.S. Department of the Interior
Minerals Management Service
Gulf of Mexico OCS Region

Safety Alert No. 231
31 May 2005

Contact: Glenn Woltman
 (504) 736-2438

Human Engineering Factors Result in Increasing Number of Riser Disconnects

A significant number of accidental riser disconnects have been experienced in deepwater operations during the last five years.  Each event had the potential for causing serious well-control issues. 

After the first incident in 2000, MMS issued a Notice to Lessees and Operators (NTL),

No. 2000-G07, which clarified 30 CFR 250.107 (a) and 250.400 (July 2002) and prescribed measures to prevent the accidental disconnect of the lower marine drilling risers from floating drilling rigs.  The NTL addressed ergonomic measures to prevent human error and offered measures focused on technological improvements.   

Since the issuance of this NTL, nine accidental drilling riser disconnects and one accidental production riser disconnect have occurred.  Two riser disconnects have occurred thus far in 2005.  Investigation results indicate human error as the cause for both incidents.    

uman error contributed to over 50 percent of the total number of events.  Failure to implement the written operating procedures to function-test the lower marine riser package (LMRP) and the BOP stack while in the moon pool or prior to water entry has resulted in many of these events.  Historical information is provided in the attached table. 

The MMS recommends that you review NTL No. 2000-G07, which states in part the following:

a.      Lock out any LMRP disconnect that is not part of a sequential disconnect process before the BOP/LMRP enters the water (ensuring that a well is secured by blind or blind-shear rams before the riser disconnects).

b.      Ensure that the sequential LMRP disconnect process, including the isolation of the wellbore, is designed so that the LMRP can be disconnected only as the result of a deliberate act.

c.      Ensure that human engineering measures such as labeling the panel button are clearly distinguishable from other functions, and fit LMRP and wellhead connector functions with securable protective covers. 

d.      Remove confusing metal tags temporarily used to identify functions, as they may have been incorrectly placed.  Rely on stamped receptacle identifications to ensure that the control circuits on the wellhead or LMRP connectors have not been disturbed.  The subsea engineer must first ensure that proper Subsea Function Test Checklist Procedures are in place, and then observe, verify, and document all function testing of the BOP’s in the moon pool.      

e.      During BOP function and pressure testing on the stump, all functions should be operated through the test stinger to confirm the hoses are installed appropriately on both pod receptacles.