Dropped Object Risk Assessment

What is a dropped object risk assessment?

A dropped object risk assessment (DORA) is a quantitative analysis of the likelihood and consequence of an object being dropped during marine lifting operations and impacting subsea or surface assets — pipelines, manifolds, wellheads, vessels, or personnel.

It is a core deliverable for offshore operators in oil & gas, offshore wind, and decommissioning campaigns where heavy lifts occur over critical infrastructure.

Why dropped object risk matters

Dropped object incidents during offshore lifts can cause:

• Loss of pipeline integrity and unplanned hydrocarbon release
• Damage to subsea trees, manifolds, or other production equipment
• Personnel injury and lost time
• Significant repair and downtime cost — often into the tens of millions for subsea repair campaigns

Quantifying this risk before a campaign begins lets operators make informed decisions about lift planning, exclusion zones, target protection, and contingency arrangements.

Standards and methodology

The de-facto industry standard is DNV-RP-F107 (Risk Assessment of Pipeline Protection). It defines a structured methodology covering:

• Drop frequency derivation from lift counts and lift type
• Object trajectory and landing distribution modelling
• Target intersection and hit frequency calculation
• Damage and release frequency by category

Supporting standards include DNV-RP-F111 (interference between trawl gear and pipelines) and operator-specific risk acceptance criteria. See the full DORAS methodology documentation for calculation detail.

Concentric rings vs grid-based analysis

Traditional implementations of DNV-RP-F107 use concentric rings around drop points to approximate the spatial distribution of landing locations. Each ring averages risk across a large band — typically 10 metres wide.

This approximation works for simple cases but loses fidelity when:

• Targets are smaller than the ring width (e.g., a wellhead or a narrow umbilical)
• Multiple drop points overlap
• Drop points are irregular shapes (e.g., a long lift path rather than a single point)

A grid-based analysis (typically 1m × 1m cells) eliminates these limitations by computing landing probability per cell and intersecting against the actual target geometry — a 100x improvement in spatial resolution over traditional concentric-ring methods.

How to conduct a defensible study

1. Define the scope — campaign location, lift types, lift counts, exposure period, targets to be assessed, and applicable risk acceptance criteria.
2. Catalogue the drop sources — every lift, drop point, and object type that contributes to the risk picture. Aggregation across sources is essential.
3. Catalogue the targets — pipelines, equipment, and any other assets at risk. Capture geometry (linear vs polygon), depth, and damage capacity.
4. Apply the calculation methodology — drop frequency, landing distribution, hit frequency, damage and release frequencies per DNV-RP-F107.
5. Compare against acceptance criteria — operator-specific or regulatory thresholds for damage / release frequency.
6. Document inputs and assumptions — every input value, assumption, and source must be traceable for review and audit.

Run your assessment with DORAS

DORAS implements every step of this workflow as a web-based platform — from drop source definition through to grid-based calculation and reporting. The 1m grid, Monte Carlo engine, and multi-source aggregation deliver materially higher fidelity than spreadsheet-based approaches.

Start a free 30-day evaluation or get in touch to discuss a specific campaign.