Introduction to Risk Assessment on Helicopter Operations

Helicopter operations play a crucial role in oil & gas exploration, drilling and production facilities located offshore, hence, safe operations of helicopters during landing and take-off assume great significance. As compared to land operations, operation of helicopters from offshore helidecks involve greater risks due to increased distances between landing sites and adverse weather conditions offshore. Environmental conditions on the offshore helidecks like wind turbulence and hot gas exhaust fumes also pose risk to the safe operations of the helicopters. Helidecks should be designed to improve the environmental conditions for safe landing and take-off.

Helicopter operations on offshore sites act as one of the main sources of risk for offshore workers. Even on highly modernized offshore sites, helicopter operations pose a serious threat to the safety of the man and material.

Bell Energy provides consultancy services for management of helicopter operation risks which include:

• Helideck Inspections (Structural, Mechanical & Fire Fighting)
• Quantitative Risk Assessment of Helicopter Operations
• Development of Emergency Response Plans

Major incidents on offshore platforms

A number of fatal incidents have taken place on the offshore sites. Offshore oil & gas installations in North Sea witnessed a series of severe accidents in 1973, 1977 and 1978, resulting in 34 fatalities.

Offshore helicopter crashes have caused loss of many lives around the globe. During 1970-2000 in Western Europe, almost 145 deaths were caused due to 19 helicopter related accidents. Out of these, almost 14 incidents occurred due to crashing of helicopters in the sea, killing almost all the people on board. The Chinook helicopter crash off Shetland in 1986 was the most devastating, resulting in the death of 44 people. The Mumbai High incident occurred in November 2015 resulting in the death of two helicopter pilots, while conducting a night landing test. In April 2016, Helicopter carrying 13 offshore workers crashed near Bergen, offshore Norway. Similar helicopter crash accidents have been reported in Nigeria in 2015.

Helicopter hazards at an offshore installation

The incidents related to the crashing of helicopters at offshore Oil & Gas sites may be attributed to many factors:

• Excessive wind turbulence due to adjacent tall structures.
• Process thermal effects e.g. turbine hot exhausts, normal and emergency hydrocarbon cold venting.
• Obstructions in the approach and departure sectors.
• Fuel spillage during refueling requiring rapid emergency response.
• Engine or cabin fire requiring emergency response by aircrew and helideck and firefighting crews on the installation.
• Personnel contact with main or tail rotors while on deck.
• Accident on the helideck, with associated passenger injuries and/or fuel spillage, requiring rapid emergency response.
• Loose items (of baggage, equipment, etc.) being sucked into rotors or air intakes by structure-induced turbulent airflow or rotor downwash.
• Flying debris e.g. from disintegrating rotor, hitting personnel following a crash.
• Aircraft or rotor-plane movements while the helicopter is on the deck after landing, (especially when the deck is subject to significant movements as on mobile installations and FPSOs in bad weather).
• Human related factors, especially, pilot error, affecting helicopter performance.
• Adverse weather conditions, including low cloud at helideck level and poor visibility.
• Mechanical failure of a helicopter on the approach, past the decision point.
• Obstructions related to the layout of the topsides structures and equipment.
• Strong vibration from collision with external structures, explosion or mechanical failure or failure of aircraft systems.
• Operational hazards such as a badly placed crane or unsecured items on or near the helideck (plastic bags, tarpaulins).
• Any deficiencies in the design and construction of the helideck.

Risk Assessment Methodology

The risks associated with the helicopter operations at offshore Oil & Gas installation are:

• Risks to personnel while they are in the air (passengers and aircrew) from collision impact, fire or drowning.
• Risks to personnel onboard an installation due to helicopter impact with the installation and possible hydrocarbon events such as fuel fires escalating to fires and explosions elsewhere.

For helicopters, In-flight risk is often assumed to be proportional to distance (or time), but there are additional components due to take-off and landing, which are assumed to be proportional to the number of flight-stages. The overall individual risk per journey is then:

Individual Risk Per Journey = Individual Risk per hour in flight x Flying Time + Individual Risk on take-off or landing x Flight Stages

Helicopter incidents statistics presented by International Oil & Gas Producers (IOGP) database provides the following values for calculation of Individual Risk

• Accident frequency in-flight: 8.5 x 10-6 per flight hour.
• Probability of fatal accident in-flight: 0.74.
• Probability of death in a fatal accident in-flight: 0.87.
• Accident frequency during take-off/landing: 2.7 x 10-6 per flight stage.
• Probability of fatal accident during take-off/landing: 0.24.
• Probability of death in a fatal accident during take-off/landing: 0.49.

Individual risk due to helicopter transportation is calculated as, the combination of the number of helicopter operations on the offshore installations and flight duration.

Apart from the risk to helicopter crew, there could be accidents involving helicopters which can cause damage to the offshore platforms. Based on the accident outcomes in North Sea, the below event tree shows the probabilities of such accidents:

The helideck is away from the process platform and such accidents resulting in helicopter crash into process equipment is highly unlikely.

The threats and consequences of a helicopter crash accident is presented below in form of Bowtie diagram: (left side represents threats which can lead to helicopter crash; right side represents the consequences due to helicopter crash)

Risk Reduction Measures / Safety Measures

The following safety measures or barriers have been identified to reduce risk of helicopter crash:

• Detailed design review of the offshore installations (Placement of tall buildings, structures, cranes, drilling derrick, hot air exhausts, flare tower, etc.).
• Detailed assessments of helideck environmental conditions for turbulence, wind conditions, emissions from turbines, hot gases and hydrocarbon gas releases.
• The helideck should be designed to provide the most favorable direction for obstacle free approach and take-off sector in relation to the prevailing wind sector through careful assessment of wind flow impact near the helideck for wind directions (installation of windsock) and conditions.
• Mechanical turbulence created by wind hitting buildings, structures and obstacles, and is in most cases predictable. A helideck location at the same level, or above surrounding structures, is therefore recommended.
• Pilot workload assessment.
• Incorporation of new improved helicopters for transportation.
• Passenger and crew wind comfort.
• Sharing/exchange of information related to incidents/accidents worldwide.
• Wind Tunnel assessment and Computational Fluid Dynamics to assess helideck environmental conditions.
• Improved maintenance of aircraft.
• Influencing human factors that affect the behavior of aircrew, helideck crew, radio operators, logistics staff and others.

The threat barriers or safety measures have been presented below:

Conclusion

The risk related to the operation of the helicopters for transportation in offshore installations is inevitable, but in recent times the accident rates have fallen worldwide due to incorporation of several safety measures. Risks to passengers and aircrew on board helicopters flying offshore are similar to those from scheduled flights in comparably-sized fixed-wing aircraft. The main risk is to helideck crew.

The risks associated with helicopter operations for transportation have come to be accepted by many workers as part of the occupational risk of working offshore. Alternatively, ships may be used for transportation, but that would involve much greater risk with increased costs and inconvenience.

A global consensus to share information related to past incidents and accidents may help all the Oil & Gas companies to learn from those incidents and mitigate the risk more effectively.

References

• BTM Fluid Mechanics
• CAA 437 - Standards for Offshore Helicopter Landing Areas, Feb 2013
• Norsok Standard, C004 – Helicopter Deck on Offshore Installations, Rev. 1, 2004
• Offshore Risk Assessment Vol 1, Principles, Modelling and Applications of QRA studies
• Offshore Technology Report 2000/089, Helicopter Safety Offshore, HSE-UK
• A Guide to Quantitative Risk Assessment for Offshore Installations, CMPT, 1999
• OGP Risk Assessment Data Directory, Report No. 434 – 11.1, March 2010