Combined Operations – Simultaneous Different Operations – Operations

Definition

Combined Operations refer to the strategic integration of two or more distinct activities at a single workstation or within a unified process step. The main objective is to streamline workflows by reducing the number of separate setups, machines, or process steps necessary to achieve production or maintenance goals. For example, in machining, a combined operation might involve drilling, tapping, and milling a part without moving it between different machines or setups, leading to substantial reductions in cycle time, material handling, and the likelihood of errors.

Simultaneous Operations (SIMOPS), on the other hand, are defined as the execution of two or more activities concurrently, either on the same workpiece, in the same workspace, or within the same facility. Unlike combined operations (which may be sequential), SIMOPS are characterized by temporal overlap—multiple operations occur at the same time. This is especially relevant in industries such as oil and gas, chemicals, aviation, and construction, where unrelated but potentially interacting tasks can introduce new hazards.

Operations in this context include any activity related to production, maintenance, construction, commissioning, decommissioning, inspection, or testing—carried out by plant personnel, contractors, or third parties.

SIMOPS is a specialized risk management term referring to scenarios where concurrent operations may interfere with each other, creating risks not present when activities are performed separately. Examples include conducting hot work near flammable materials transfer, or performing confined space entry while nearby systems are operational. Regulatory frameworks such as those of the International Civil Aviation Organization (ICAO) underscore the necessity of systematic hazard identification and risk mitigation for such scenarios.

Background and Conceptual Overview

The principles of combined and simultaneous operations stem from industrial engineering and risk management. In production and maintenance, efficiency is often achieved by combining operations—integrating assembly steps or automating sequential processes. Such practices lead to gains in productivity, quality, and cost control, especially in advanced manufacturing environments with flexible systems (like CNC machines and robotics) performing multiple steps in a single cycle.

Simultaneous operations (SIMOPS) arise when multiple activities need to be carried out concurrently, often due to tight schedules, maintenance requirements, or the need to keep legacy systems running during upgrades or expansions. This is typical in brownfield projects, plant turnarounds, and large-scale construction, where new and existing operations must coexist.

ICAO documentation and other industry standards highlight that overlapping activities introduce complex hazards. The interaction between teams, tools, and processes can create emergent risks—those unique to the simultaneous execution of tasks. This has led to the development of rigorous SIMOPS identification, assessment, and control processes, including integrated permit-to-work systems, multidisciplinary planning, and detailed risk assessments.

Key Terminology

ICAO and other industry guidance further define these terms for aviation, manufacturing, and process environments, emphasizing their application in airside construction, maintenance, and emergency response.

Types of Combined and Simultaneous Operations

Combined Operations

• Sequential Combination: Multiple operations executed in a specific order within one setup—e.g., drilling, tapping, and deburring a part without moving it.
• Integrated Combination: Equipment or process design allows several tasks to run in parallel within a single machine cycle—e.g., CNCs milling and boring features simultaneously.

Combined operations are prevalent in automotive and aerospace manufacturing, where throughput and accuracy are critical. Automation reduces manual handling, improving both efficiency and safety.

Simultaneous Operations (SIMOPS)

• Parallel Operations: Distinct teams perform different tasks in proximity—e.g., aircraft maintenance while refueling and baggage handling.
• Overlapping Work: Activities occur on the same asset—e.g., hot work on a pipeline while adjacent lines remain active.
• Multidisciplinary SIMOPS: Various teams (operations, maintenance, contractors) work at once, requiring strong coordination.

In aviation (per ICAO), SIMOPS are managed during runway maintenance, terminal construction, or emergency response, ensuring aircraft and ground operations remain safe.

How Combined and Simultaneous Operations are Used

Combined Operations in Manufacturing

• Machining and Assembly: Single CNCs execute drilling, threading, and milling in one setup, minimizing errors and cycle time.
• Automation: Robots and PLCs execute overlapping tasks (e.g., welding, painting, inspection) in a single cell.
• Assembly Cells: Automotive lines integrate wiring, sensors, and trim installation into one operation, increasing throughput.

SIMOPS in Industrial and Construction Settings

• Plant Turnarounds: Hundreds of maintenance, inspection, and modification activities run concurrently, maximizing downtime use but increasing risk.
• Construction Projects: New facilities built while existing operations continue—e.g., airport runway resurfacing during regular flights.
• Routine Maintenance: Critical infrastructure often requires ongoing operations during maintenance, managed with careful SIMOPS controls.

ICAO standards require SIMOPS controls in airport construction and maintenance, where aircraft and construction activity must be safely coordinated.

Typical Scenarios and Use Cases

Manufacturing Examples

• Combined Machining: Multi-axis CNCs perform drilling, tapping, and milling in one setup, critical for aerospace and precision industries.
• Simultaneous Assembly: Multiple robots in an automotive cell install doors, wiring, and dashboards concurrently.

Process Industry Examples

• Oil & Gas Platforms: Maintenance like welding or electrical work occurs alongside hydrocarbon production—requiring strict SIMOPS planning.
• Chemical Facilities: Construction and tie-ins near live operations, such as crane lifts over storage tanks, demand careful integration and controls.
• Paper Mills: Maintenance in connected vessels can result in hazardous interactions if not properly coordinated.

Construction and Maintenance

• Shutdowns/Turnarounds: Multiple contractors perform overlapping repairs and calibrations in close quarters.
• Commissioning: Bringing new systems online while others remain operational—e.g., electrical testing affecting adjacent plant areas.
• Emergency Response: Repairs after incidents must be managed alongside ongoing operations for safety.

Risks and Hazards Associated with SIMOPS

SIMOPS create unique risks from the interaction of activities, people, and equipment. Poor management can lead to severe incidents—injuries, fatalities, property damage, or environmental harm.

Potential Hazardous Consequences

• Personnel Injury: Overlapping activities can expose workers to falls, burns, toxic fumes, or impact.
• Property Damage: Fires, explosions, or equipment damage from unintended activity interactions.
• Environmental Impact: Releases of toxic gases or flammable liquids may occur if containment is compromised.

Common Risk Factors

• Lack of coordination and central authority.
• Unrecognized interactions between activities.
• Permit overlaps not accounting for SIMOPS.
• Multiple contractors with differing safety cultures.
• Restricted egress or blocked escape routes.

Notable Incidents

• Wacker Polysilicon (2020): Fatal HCl release during simultaneous maintenance and insulation work; inadequate coordination and escape planning.
• Evergreen Packaging Mill (2020): Fatal fire due to incompatible maintenance methods in interconnected vessels.

SIMOPS Identification and Review Process

A SIMOPS Review is a structured process required by ICAO and other standards for any planned simultaneous activities.

Key Steps

1. Identify Overlapping Activities: Map schedules and permits to detect concurrent work.
2. Collect Activity Information: Assemble safety data, procedures, and hazard analyses.
3. Identify Potential Interactions: Analyze direct and indirect hazards between activities.
4. Assess Risks: Use risk matrices tailored for SIMOPS.
5. Review Existing Controls: Check if current safeguards are sufficient.
6. Develop Additional Controls: Specify new procedures, supervision, or scheduling changes.
7. Document and Communicate: Ensure all controls are recorded and understood by stakeholders.
8. Monitor and Audit: Continuously review effectiveness and capture lessons learned.

ICAO recommends integrating SIMOPS reviews into routine and non-routine planning, especially for airside projects.

Lifecycle and Stepwise Management of SIMOPS

Effective SIMOPS management follows a lifecycle approach paralleling hazard identification and risk analysis, but focuses on activity interactions.

SIMOPS HIRA Process Steps

1. Identify SIMOPS Activities: Use planning tools and meetings to highlight overlaps.
2. Collect Information: Gather technical specs, hazard analyses, and team lists.
3. Identify Interactions: List possible mechanical, chemical, or access interferences.
4. Analyze Hazardous Consequences: Consider worst-case scenarios.
5. Review Existing Safeguards: Assess current controls—isolations, alarms, emergency plans.
6. Specify New Controls: Add fire barriers, detect systems, new work sequences, or extra supervision.
7. Plan SIMOPS Governance: Define integrated procedures and emergency responses.
8. Communicate the Plan: Conduct briefings and toolbox talks with all parties.
9. Execute and Monitor: Carry out activities under carefully managed controls.
10. Conclude Activities: Safely wrap up and remove temporary controls.
11. Audit and Improve: Review incidents and near-misses for future learning.

SIMOPS Management Checklist

Conclusion

Combined Operations and Simultaneous Operations (SIMOPS) are essential concepts in modern industrial, manufacturing, and construction environments. While combined operations streamline workflows and improve efficiency by integrating multiple steps, SIMOPS require robust risk management to prevent hazardous interactions between concurrent activities. Adhering to international standards—such as those outlined by ICAO—and implementing structured SIMOPS review processes are critical to ensuring safety, minimizing downtime, and maintaining operational integrity.

Further Reading

• International Civil Aviation Organization (ICAO) Safety Management Manuals
• International Association of Oil & Gas Producers (IOGP) SIMOPS Guidelines
• OSHA Process Safety Management Standards

For guidance on implementing combined operations and SIMOPS controls in your facility, contact our operations safety experts.