Permit to Work and Job Safety Analysis for a Slickline Job: A Practical HSE Guide for Engineers and Supervisors

Educational content only: procedures and operating values vary between companies and wells. Always follow your company’s approved procedures, your supervisor’s instructions and the permits in force at your site.

Why do we need a formal system?

Well intervention, such as slickline and e-line, is often carried out on a producing well connected to an operating facility. There is live pressure in the christmas tree, flammable and possibly toxic gases, a service crew unfamiliar with the facility, and a facility crew unfamiliar with the service tools. In these conditions individual care is not enough. We need a system that ensures everyone knows what will happen, where and when; that energy sources are isolated; that the work does not clash with other nearby work; and that the plant returns to a safe state at the end.

The UK Health and Safety Executive (HSE) notes in its HSG250 guidance that many major accidents in the hazardous industries have been linked to failures of permit-to-work systems, such as poor communication at shift handover, incomplete isolation, or simultaneous activities that were not coordinated.

The permit-to-work cycle, step by step

1. Request and planning: the performing party (service supervisor) defines the scope, location, duration and equipment, and submits it to the facility's responsible person.
2. Risk assessment: the job safety analysis is prepared and the cross-referenced certificates identified, such as an isolation certificate, gas test or hot-work permit if needed.
3. Isolation and preparation: the facility crew isolates the well from the production system as required, applies locks and tags to valves (lock-out / tag-out), and verifies the isolation.
4. Issue: the authorised person reviews and signs the permit, and the performing party signs to confirm understanding of the conditions. The permit is explained to the crew at the pre-job meeting.
5. Execution and monitoring: the permit is displayed at the worksite and its conditions, such as continuous gas monitoring, are maintained. Any change triggers a stop and review.
6. Handover or suspension: at shift change or when work stops, the permit is handed over clearly between supervisors, stating the status of the job and the well.
7. Close-out: when the work is finished, both parties confirm the site is clean, isolations have been correctly removed, and the well is in the agreed state. The permit is then closed and filed.

Job safety analysis (JSA): the method

A JSA breaks the work into sequential steps. For each step we ask: what can go wrong? Who could be hurt? What controls are in place? What additional controls are needed? Who is responsible for each? OSHA's sample JSA worksheet for oil and gas offers a simple three-column structure: job step, potential hazard, and preventive action.

The order of controls matters. Start by eliminating the hazard if possible, then substitution, then engineering controls such as barriers and valves, then administrative controls such as procedures, permits and training, and finally personal protective equipment. PPE is the last line of defence, not the first.

Hazards and controls table for a typical slickline job

Hydrogen sulphide (H2S): the numbers you must know

H2S is colourless, heavier than air, and smells of rotten eggs at low concentrations. But it deadens the sense of smell at higher concentrations, so smell must never be relied upon. The UK workplace exposure limits table EH40 sets:

• 5 ppm: 8-hour time-weighted average (TWA).
• 10 ppm: 15-minute short-term exposure limit (STEL).

Companies usually set detector alarm levels at or below these values and define in the emergency plan what to do at each level. Legal limits differ between countries. The UK HSE document OCE6 explains H2S hazards in the offshore industry, why it forms, and how to monitor and protect against it.

In sour wells, the effect of H2S on metals must also be considered: it can embrittle some steels. Pressure equipment and wire must be suitable for sour service.

Isolation and bleed-off: the heart of slickline safety

OSHA's eTool for special services lists among key practices bleeding off lubricator pressure before breaking connections, securing pressurised equipment, and careful handling of stored energy. In practice:

• No connection is broken until the gauge confirms zero pressure, with the bleed valve open and routed to a safe place.
• Isolated valves are locked and tagged, and only the person named in the permit operates them.
• It is clear who owns each valve: the facility crew or the service crew.
• When in doubt, stop until the situation is clear.

Roles and responsibilities

A permit system works only if everyone knows their role. Titles vary between companies, but the core roles are similar:

• Issuing / area authority: a facility person who knows the area and its systems. Approves the work, verifies isolation and oversees simultaneous operations.
• Performing authority: the service crew supervisor. Responsible for carrying out the work per the permit, briefing the crew on the conditions and reporting any change.
• Isolating authority: carries out, verifies and records isolations, usually from the facility crew.
• Gas tester: tests the atmosphere before and during the work as the conditions require.
• Crew members: attend the meeting, understand the hazards, follow the controls and use their stop-work authority.

A worked JSA line in detail

Take the step "tools out and breaking the lubricator" and analyse it in depth, because many incidents happen here:

• Step: pull the tools into the lubricator, close the upper tree valve, then break the quick union to remove the tools.
• What can go wrong? The tools may not be fully inside the lubricator, so the valve closes on wire or tool. The valve may not seal, leaving pressure. Someone may forget to bleed off, so the connection parts under pressure, releasing components and fluid.
• Who could be hurt? The person breaking the connection and anyone nearby, as well as anyone working below the equipment.
• Controls: confirm the tools are in by a wire mark, the depth counter and the feel of the tool reaching the stuffing box. Close the valve the correct number of turns. Bleed off through the bleed valve to a safe place and watch the gauge reach zero and stay there. Stay out of the line of the connection. Use the proper breaking tool.
• Responsible: the slickline unit operator for bleed-off, and the service supervisor for verification before breaking.

Simultaneous operations (SIMOPS)

On large facilities, slickline may run on one well while lifting, welding or maintenance happens nearby, or while neighbouring wells produce. The issuing authority must look at the full picture: does nearby hot work conflict with a possible gas release from the well? Will the facility crane pass over the slickline crew? A SIMOPS matrix is commonly used to define what may run together and what may not.

Dropped objects

Working on the tree and lubricator means tools and equipment above the crew's heads. The DROPS programme offers practical resources for preventing dropped objects, including tethering hand tools when working at height, inspecting fixed equipment before and after the work, and setting a drop zone below the work.

When the gas alarm sounds

Each site's emergency plan defines the exact steps. The general idea: on alarm, work stops, the well is made safe if this can be done safely, the crew moves upwind to the muster point, and nobody returns except with breathing apparatus and permission from the person in charge after the atmosphere has been tested.

Pre-job meeting: a short checklist

• Explain the scope, the permit and its conditions, and who signs what.
• Review the JSA steps, the controls and who is responsible for them.
• Well status: pressures, presence of H2S, valve positions and isolation.
• Exclusion zones, wind direction and the muster point.
• Emergency and communication plan, and the location of breathing apparatus and fire equipment.
• Nearby simultaneous operations and how they will be coordinated.
• A reminder of every crew member's stop-work authority.

Common mistakes in permit systems

• Treating the permit as paperwork signed without visiting the site.
• Copying an old risk analysis without adapting it to the current well.
• Rushed verbal shift handovers without reviewing the status of the work.
• Starting work before isolation has actually been verified.
• Closing the permit before the well and plant are returned to a safe state.

Summary for the engineer and supervisor

A permit system and a risk analysis do not prevent accidents on their own. What prevents them is real application: being at the site, verifying with your eyes and the gauge, clear communication, and the courage to stop the job. See the gauge cutter article to understand the operation itself, and the christmas tree valve sequence article to understand isolation.

Test your understanding

Glossary terms

• Slickline
• E-line
• Lubricator
• Christmas Tree
• BOP

Related lessons

• Slickline in detail: tools and fishing
• What is E-line and how does it work inside the well?
• Workover operations: from well failure to production restart
• What Is a BOP? Quick Introduction

Sources

1. UK HSE - HSG250: Guidance on permit-to-work systems
2. UK HSE - Human factors: permit-to-work systems
3. UK HSE - EH40/2005 Workplace exposure limits (H2S: 5 ppm 8-h TWA, 10 ppm 15-min STEL)
4. UK HSE - OCE6: Hydrogen sulphide in the offshore industry
5. OSHA eTool - Job Safety Analysis sample worksheet
6. OSHA eTool - Special services: wireline operations hazards and controls
7. Energy Safety Canada - IRP 13: Wireline Operations (Ed. 2, 2020)
8. DROPS - Dropped Objects Prevention Scheme (resources)