What are the 3 most important changes to maritime gas detection rules?

  • Door Lavastica

The 3 most important recent changes to maritime gas detection rules are: CO2 is now a mandatory pre-entry testing parameter, connected and adjacent spaces must be independently assessed, and the Permit to Work system now has a strict 8-hour validity limit. These changes stem from IMO Resolution MSC 581(110), which was endorsed on 3 December 2025 and officially replaces the older Resolution A 1050(27). The sections below break down each change and explain what they mean for your vessel and your crew.

Which regulatory bodies govern maritime gas detection requirements?

Maritime gas detection requirements are governed primarily by the International Maritime Organization (IMO), which sets binding international standards through SOLAS (Safety of Life at Sea) and IMO Resolutions. Classification societies such as DNV, Lloyd’s Register, and Bureau Veritas translate these standards into technical requirements for individual vessels, while Port State Control authorities enforce compliance during inspections.

SOLAS Regulation XI-1/7 requires ships to carry portable gas detection systems, and SOLAS Regulation III/19 mandates enclosed space entry and rescue drills. For many years, the industry relied on IMO Resolution A 1050(27) as the practical guide for enclosed space entry procedures. That resolution has now been superseded by MSC 581(110), which closes the gap between basic SOLAS requirements and modern technical realities.

RightShip has also moved quickly. Its RiSQ version 3.2 inspection framework has already integrated the MSC 581(110) requirements into its scope, meaning vessels are being assessed against the new standard during commercial vetting processes as well as official Port State Control inspections.

What are the 3 most important recent changes to gas detection rules?

The three most important changes introduced by IMO Resolution MSC 581(110) are the mandatory inclusion of CO2 as a pre-entry testing gas, the expanded definition and independent assessment of connected and adjacent spaces, and the tightened Permit to Work rules. Together, these changes represent a significant shift from the previous regime and require action from every fleet engineer and technical superintendent.

Change 1: CO2 is now a mandatory pre-entry testing parameter

Under the previous standard, a standard 4-in-1 detector measuring O2, LEL, CO, and H2S was considered sufficient for enclosed space entry. That is no longer the case. MSC 581(110) requires CO2 to be confirmed below 0.5% (5,000 ppm) before any entry is permitted.

The problem is that most legacy 4-in-1 units cannot detect CO2 at all. Standard electrochemical sensors also lack the resolution to accurately measure concentrations at the ppm level. Non-Dispersive Infrared (NDIR) technology is now the benchmark for compliance, as it provides the high-resolution ppm monitoring needed to detect dangerous CO2 buildup before it becomes fatal. The regulation also highlights a risk that many crews underestimate: ordinary rusting in a damp, confined space can rapidly consume oxygen and elevate CO2 to lethal levels. A space does not need to carry hazardous cargo to become dangerous.

Change 2: Connected and adjacent spaces must be independently assessed

MSC 581(110) significantly expands the definition of what counts as a risk area. A connected space is any area linked by a door, trunk, manhole, pipe, or even a small gap, because an airtight seal cannot be verified from the outside. An adjacent space is any area sharing a common bulkhead with a hazardous atmosphere, where gas can migrate through corrosion, coating damage, or weld seepage.

Both types of space must be treated as hazardous until proven otherwise, independently ventilated, and individually tested. Even after a main compartment has been cleared, gas can remain trapped in vertical trunks or structural dead-ends. Every connection point requires its own risk assessment and its own confirmed atmospheric test before entry is allowed.

Change 3: Permit to Work rules are now significantly stricter

The Permit to Work system has been tightened to eliminate human error. Key hard rules now include:

  • Maximum permit validity of 8 hours — if the work team takes a break or ventilation stops, the permit is immediately void
  • Full re-assessment and re-test required before work may continue after any interruption
  • Entrances must be physically marked with SAFE or UNSAFE signs
  • Hazardous entry points must be physically locked when no active permit is in place
  • Solo entry is prohibited — a trained attendant must always be stationed at the entrance
  • Unplanned rescue attempts are strictly prohibited — EEBDs are for escape only, never for rescue entry

For Port State Control inspectors, an unrecorded atmospheric test is treated as a test that did not occur. Every re-entry result must be formally recorded.

Which vessel types are most affected by these rule changes?

Bulk carriers, tankers, and general cargo vessels are most directly affected by MSC 581(110), because their operations involve frequent enclosed space entry into cargo holds, tanks, and void spaces where oxygen depletion and CO2 buildup are most likely to occur. However, the regulation applies to all vessel types covered by SOLAS.

Vessels carrying cargo that depletes oxygen or emits toxins face the highest immediate risk, but the regulation specifically draws attention to the fact that any vessel with damp, confined steel spaces is at risk. A cargo of scrap metal, or simply the ship’s own structural steelwork in a humid hold, can create an asphyxiation hazard within days through the oxidation process. This means the new rules are relevant to a much wider range of vessels than many fleet engineers initially assume.

How do the new rules affect existing onboard gas detection systems?

The new rules mean that most existing 4-in-1 gas detectors are no longer sufficient on their own for enclosed space entry compliance. Ships that rely exclusively on legacy units measuring LEL, O2, CO, and H2S will need to add CO2 detection capability to meet the requirements of MSC 581(110).

The recommended compliance path is practical and cost-effective: rather than replacing an entire fleet of functional, calibrated 4-in-1 detectors, you can supplement existing equipment with a dedicated standalone CO2 detector. This bridges the regulatory gap without the capital expenditure of a full fleet replacement. The standalone unit must use NDIR technology to accurately measure CO2 at the 5,000 ppm threshold.

Beyond the detector itself, MSC 581(110) introduces two important administrative requirements that affect how you manage your systems. First, a mandatory vessel-specific Enclosed Space Register must be maintained both on board and synchronized with the shore-side office in real time, updated immediately whenever cargo changes or the purpose of a space is altered. Second, a dedicated Enclosed Space Emergency Response Plan must be documented and verified by the master before any entry permit is issued. Your service and repair schedule should be reviewed in light of these new documentation requirements.

What should fleet engineers do to stay ahead of gas detection compliance?

Fleet engineers should take five immediate actions to align with MSC 581(110): audit existing gas detection equipment, update the Safety Management System, formalize the Enclosed Space Register, strengthen training and drills, and enforce entrance control. Acting now avoids costly deficiencies during Port State Control inspections and protects crew safety.

  1. Audit all gas detection equipment — confirm whether your current units can test CO2 in the 0-5% volume range. If you only have 4-in-1 detectors, procure standalone NDIR-based CO2 detectors immediately.
  2. Revise your Safety Management System (SMS) — update shipboard procedures and risk assessment forms to align with MSC 581(110), including the expanded definitions of connected and adjacent spaces.
  3. Formalize the Enclosed Space Register — ensure it includes all connected and adjacent spaces with their specific ventilation requirements, hazard sources, gas testing points, and estimated gas exchange times.
  4. Conduct training and drills every two months — drills must go beyond simple muster to include practical use of atmospheric testing instruments and resuscitation techniques. Crew members must understand that connected spaces require independent atmospheric testing.
  5. Enforce entrance control — ensure all manholes are locked or sealed unless an active permit is in place, and that SAFE/UNSAFE signage is physically present at every entry point.

How we help with gas detection compliance

At Lavastica, we work with fleet engineers and technical superintendents every day who are navigating exactly these kinds of regulatory changes. Here is what we can do for you:

  • Supply standalone CO2 detectors with NDIR technology that integrate with your existing 4-in-1 setup, so you achieve compliance without replacing functional equipment
  • Advise on compatibility between new detectors and your current onboard systems and panels
  • Deliver fast, worldwide from our Rotterdam warehouse to minimize port days
  • Provide technical support on which products meet MSC 581(110) requirements and classification society standards
  • Support retrofit and commissioning when you need hands-on assistance with installation and system integration

Want to know exactly which CO2 detector works with your current setup? Get in touch with us directly. Learn more about who we are or contact us for fast, no-nonsense advice from people who know maritime safety inside out.

Phone: +31 (0) 10 265 5070Email: [email protected]

Related Articles