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Vented Gas Detection

Vented Gas Detection

The venting of combustible gas from OCS facilities during emergency drilling and production upsets is a BSEE approved safety precaution and a routine occurrence on offshore oil and gas facilities. Over 400 of the OCS's 2000 plus offshore facilities have helidecks designed for the safe transport of facility personnel, BSEE inspectors, emergency responders and other essential personnel and supplies by helicopter. One of the dangers of helicopter flight to and from OCS facilities is the potential for vented gas ingestion by helicopter engines during landing and takeoff. Ingestion of methane gas (and other associated petroleum gases) are known to cause surging, compressor stall, and/or flameout of helicopter engines.

On August 26, 2014, a Safety Recommendation issued by the National Transportation Safety Board (NTSB) included five safety recommendations to BSEE, one of which was to identify and develop a comprehensive system and procedures to mitigate the risk of ingestion of platform vented gas by helicopters operating in the vicinity of offshore oil and gas facilities.

In response, BSEE funded Study No. 733 under the BSEE Technology Assessment Program (TAP), titled “Aviation Safety Support Services for the Bureau of Safety and Environmental Enforcement2. The contractor, PWC, performed multiple tasks including Subtasks C.4.5.1, C.4.5.2 and C.4.5.3 (below) which apply to this BAST Assessment.

Subtask C.4.5.1 – review and assess helideck construction standards: In this subtask a review of current U.S. and international regulations and standards was performed addressing the placement of gas vents in relation to helidecks. A comprehensive examination of U.S. regulatory agencies and statutes revealed that there are no regulatory requirements or guidance promulgated by these agencies for mitigation of hazards posed by associated petroleum gas (APG). However, it was noticed that the recommendations provided in API 14-J: Recommended Practice for Design and Hazard Analysis for Offshore Production Facilities 2nd edition and the draft version of API 2L-1: Recommended Practice for Planning, Designing, and Constructing Heliports for Fixed Offshore Platforms are sufficiently comprehensive to ensure that hazards presented by APG are considered and mitigated. Additionally it was noted that placement of helidecks, cranes, living accommodations and flare discharge locations varies widely from one OCS facility to another.

Subtask C.4.5.2 – technical analysis: As discussed in this Subtask, the maximum permissible concentration of hydrocarbon gas within the helicopter operating area is 10% of the lower flammable limit (LFL). According to the report, the LFL for methane is 4.4% by volume; thus 10% LFL for methane is 0.44%. Additionally, as mentioned in the report, this low methane concentration (0.44%) has the potential to cause helicopter engines to surge and/or flameout. Based on PWC findings regarding the threat posed by vented gas, it was concluded that until a computational fluid dynamics (CFD) gas dispersion model is constructed for each facility, in accordance with the recommendation in Subtask C.4.5.1, helidecks should be considered contaminated with APG whenever the wind direction is within 10 degrees of the platform’s designated flaring/venting critical wind zone and the facility is cold venting APG.

Subtask C.4.5.3 - monitoring and warning systems: This part of the study identified and evaluated (1) technologies to monitor combustible gases that could adversely affect helicopter operations in the vicinity of an OCS facility; (2) how a sensor for vented gas can be devised/installed around the helidecks and oil rigs to advise pilots of the quality of the environment they intend to fly through on takeoff and landing; and (3) mitigation strategies such as installing diffusers or other systems on vent stacks that would reduce the risk of methane or combustible gases.

The PWC report concluded that several mature hydrocarbon gas detection technologies were being used in offshore, petrochemical, and other hydrocarbon facilities that could also address concerns with helicopter engine safety issue.  Furthermore, the study showed (1) that installation of point and open-path gas detectors could be installed on the helideck perimeter and in the path from the APG source (e.g., emergency boom) to the helideck and (2) that installation of a helideck visual warning indication system as discussed in API RP 2L-1: Recommended Practice for Planning, Designing, and Constructing Heliports for Fixed Offshore Platforms, 5th Edition, should be considered. More information on these monitoring technologies is provided later in this report.

In summary, the PWC report recommended that, in order to minimize or eliminate the risks presented to helicopter operations due to the release of methane or other combustible gases on OCS facilities, BSEE should explore the use of methane gas detection devices as a way to provide early warning to helicopter pilots and facility personnel.

In response to PWC’s recommendation and in the interest of safety the Chief of the Office of Regulatory Programs (ORP) proposed to the BSEE Director by memo dated November 13, 2015, that an assessment under the BSEE BAST Determination Process be initiated on gas detection technologies for possible use on the OCS during helicopter transportation of personnel. The Director concurred and the ORP initiated an MGD assessment in January of 2016. The following timeline illustrates the individual steps of the BAST Process.

MGD Timeline

To date, the first five steps of the BAST DP have been completed or are in process of completion, as follows:

STEP 1.1: SAFETY ISSUE: BSEE’s review of related OCS incidents to determine whether sufficient evidence supports earlier BSEE findings that a potential safety issue exists on the OCS. BSEE concluded that such a safety issue exists.

STEP 1.2: ASSESSMENT AND FINDINGS: BSEE initiated Step 1.2 – Assessment of the BAST DP to determine whether technology solutions exist that could mitigate the safety issue identified from Step 1.1 above. BSEE met with a variety of stakeholders, including operators and Original Equipment Manufacturers (OEMs) of gas detection equipment, to evaluate systems on the open market with applicability to OCS operations that can be installed at/near the point of methane gas release or at/near the helideck to provide early warning to helicopter pilots. From these discussions BSEE determined that various MGD systems were commercially available to mitigate the inherent danger of the release of gas to approaching or departing helicopters.

STEP 1.3: BAST FEASIBILITY ANALYSIS: BSEE Directors’ finding from the BAST Assessment conducted in Step 1.2.  Director concluded that it is likely that there are cost-effective technologies that will mitigate the potential safety issue and to proceed with the BAST Determination.

STEP 1.4: TECHNOLOGY IMPROVEMENT OBJECTIVE: BSEE developed the following Technology Improvement Objective (TIO) which has the potential to improve safety, health or environmental protection associated with the ingestion of methane gas into helicopter turbine engines during landing and departure from OCS platforms.

Based on an evaluation of commercially available technology, what is the lowest level of methane (at or above the Lower Flammability Limit) that can be detected in a cost effective and feasible manner in the vicinity of the helidecks?

STEP 1.5: PUBLIC NOTICE DOCUMENT: BSEE’s Public Announcement of intent to evaluate MGD under the BAST Determination Process. BSEE presented their work to date and the MGD TIO at the April 17th BAST Technology Solutions Forum in Houston to allow for open dialogue and stakeholder feedback. The Forum generated a series of questions which BSEE provided answers to during the Forum.

STEP 1.6. EVALUATE COMMENTS: Upon the receipt of public comments under Step 1.5 above, BSEE evaluated all comments and incorporated many in order to improve the quality and direction of the BAST Determination Process.

STEP 1.7. CONTINUE BAST DETERMINATION: Based on BSEE’s review of the TIO comments and on comments received during and after the April 17th BAST Technology Solutions Forum, the Director will decide whether to continue the BAST Determination Process.


Comments on the BAST Program and/or on the VGD BAST Determination can be provided via BSEE’s BAST webmail address (

1 NTSB recommended to USCG to work with BSEE to identify and develop comprehensive systems and procedures to mitigate the risk of ingestion of raw gas discharges, such as methane, by helicopters operating in the vicinity of offshore oil platforms: