IMCA M 140 Explained: The Safety Standard Every ROV Pilot Must Know

IMCA M 140 ('The Inspection, Maintenance and Repair of Subsea Structures Using Diving and ROV Techniques') is the principal IMCA document governing ROV operations safety. If D 036 tells you how to qualify people, M 140 tells you how to run safe operations. Here's what it actually says and what it means in practice.

Scope and Purpose

M 140 covers the planning, execution, and documentation of ROV-based inspection, maintenance, and repair (IMR) operations on subsea structures. It is not an equipment standard or a training document — it is an operational guidance document that defines safe working practices.

Like D 036, M 140 is guidance rather than mandatory regulation. But IMCA member contractors apply it, and clients cite it in their specifications. Deviation from M 140 practice requires documented justification.

Key Requirements: Planning

M 140 places significant emphasis on pre-dive planning. The document requires that the following be established before any ROV operation commences:

• Written dive program or work scope — what is to be done, in what sequence, to what standard
• Environmental assessment — currents, visibility, seabed conditions, obstructions
• Equipment check — vehicle and topside systems confirmed fit for purpose before deployment
• Personnel competency confirmation — all operating personnel hold the required IMCA grade for the work
• Emergency and contingency planning — defined responses to vehicle loss, entanglement, or equipment failure
• Communication protocol — clear lines between pilot, supervisor, vessel bridge, and client representative

Key Requirements: Execution

During operations, M 140 requires:

• Continuous monitoring of vehicle and umbilical status
• Real-time logging of operational data (depth, time, observations)
• Defined abort criteria communicated to the operating team before dive commencement
• Supervisor authority over operational decisions — not subject to override by client representatives on safety matters
• Fatigue management — crew rotation and rest periods are an operational requirement, not a preference

Key Requirements: Documentation

The documentation requirements in M 140 align with and reinforce what was discussed in the IMCA dive log requirements article. Key points:

• Dive logs must be completed for every operation, including aborted dives
• All required fields must be completed — partial logs are non-compliant
• Supervisor sign-off is mandatory
• Records must be retained for a minimum period (client contract requirements often extend beyond IMCA minimums)
• Equipment maintenance records must be maintained in parallel with dive logs

What M 140 Says About Client Pressure

One of the most important aspects of M 140 is its clarity on the relationship between operational safety decisions and commercial pressure. The document is explicit: the ROV Supervisor has the authority to stop or limit operations for safety reasons, and this authority cannot be delegated away or overridden by contractual or commercial considerations.

Applying M 140 in Daily Operations

M 140 compliance is not primarily about the audit — it's about running operations that don't result in incidents. Teams that internalize the planning requirements, maintain proper documentation habits, and respect operational decision-making authority tend to have better safety records and better client relationships over the long term.

Using structured tools like ThrusterLog for dive logging, shift notes, and certification management supports M 140 compliance by making the documentation discipline easier to maintain consistently — including on long campaigns when administrative fatigue sets in.