The Permit to Work (PTW) system formally controls potentially hazardous work. Safe electrical isolation protects workers from electrical hazards and prevents accidental energisation during maintenance. This unit covers PTW essentials, the TEST-PROVE-reTEST method, Lock Out Tag Out, and CVT assessment procedures for EX01–EX04.
Learning Objectives
Define a Permit to Work system and its essential features
State the types of work that require a PTW
Describe the TEST-PROVE-reTEST safe isolation method and explain why each step is essential
Describe Lock Out Tag Out (LOTO) and multi-trade isolation requirements
State the hand-back procedure for PTW closure
Complete a PTW and gas free test certificate for a CVT scenario
Permit to Work — Purpose
A Permit to Work is a formal recorded process used to control potentially hazardous work. It is both a safety management tool and a communication system between installation management, plant supervisors, and those performing the work.
Essential features:
Clear identification of who may authorise work and who specifies precautions
Training in issue, use, and closure of permits
Monitoring and auditing to confirm the system works as intended
Standardised identification of tasks, risks, duration, and control measures
When is a PTW Required?
PTWs are required for work that may adversely affect safety of personnel, plant, or environment:
Work generating heat, sparks, or other ignition sources
Breaking containment of flammable, toxic, or pressurised systems
High voltage electrical work
Entry into tanks and confined spaces
Work at height, diving operations, pressure testing
Work affecting evacuation or rescue systems
Any other potentially high-risk operation
TEST-PROVE-reTEST (Sandwich Test)
TEST (Prove the instrument) — confirm voltage tester works on a known live supply before testing the isolation
PROVE dead — test the isolation point; confirm zero volts on all conductors including neutral
reTEST (Re-prove) — confirm the instrument still works on the known live supply after the test
Both checks on the known live source are essential — a faulty instrument that reads zero on a live circuit would not be detected without the sandwich structure.
⚠ All Conductors Including Neutral Must Be Isolated
The neutral conductor must be isolated and confirmed dead. Under fault conditions, an isolated neutral can still carry current through other fault paths.
Lock Out Tag Out (LOTO)
After proving isolation:
Each person working applies their own personal padlock to the isolation point
The isolation device cannot be closed until ALL padlocks are removed
Tags identify who has isolated and why
Multi-trade: all trades apply their own locks simultaneously — no single trade can re-energise while another's lock remains
No person may remove another person's padlock
PTW Display and Hand-back
PTW copies must be displayed at: (1) the work site; (2) the central/main control room; (3) with the issuing authority or area authority.
Hand-back procedure — three confirmations before PTW closure:
Work completed — confirmed by performing authority
Plant returned to safe condition — isolations removed and verified; confirmed by responsible authority
Production staff acknowledges — return of plant to their control confirmed
Then the permit is formally cancelled and signed by the authorised person.
Quick Check — 5 Questions
Test key concepts from this unit before moving on.
Q1Summary
Primary purpose of a PTW system?
A PTW formally manages the communication and control between all parties — ensuring safety precautions are specified, implemented, and verified before work begins, and that plant is safely returned to service after completion.Ref: PTW System
Q2Summary
Why must the neutral conductor be isolated during Ex installation maintenance?
The neutral conductor must be isolated and confirmed dead. Under certain fault conditions (broken neutral in another circuit, backfeed, floating neutral), the neutral can be live even when the supply is isolated. All conductors must be confirmed dead.Ref: IEC 60079-17 / Safe Isolation
Q3Summary
A second trade (mechanical) arrives at an already-isolated motor. What LOTO action is required?
Each trade applies their own personal padlock. Neither can re-energise while the other's lock remains — even if one trade thinks their work is complete. Protects each trade independently.Ref: PTW / LOTO
Q4Summary
Where must copies of a PTW be kept during work?
Three locations: work site (with performing authority if multiple locations), central control room (so operators know which plant is under permit), and with the issuing authority.Ref: PTW Display
Q5Summary
What is the PTW hand-back procedure and when is it completed?
Hand-back: (1) work confirmed complete; (2) plant returned to safe condition with isolations verified removed; (3) production staff acknowledge return of plant control. Then PTW formally cancelled by authorised person.Ref: PTW Hand-back
EX Academy — independent CompEx-style preparation. Not official CompEx course materials.
Unit 14 · CVT & Assessment · Full Manual
Permit to Work & Safe Isolation
The Permit to Work (PTW) system formally controls potentially hazardous work. Safe electrical isolation protects workers from electrical hazards and prevents accidental energisation during maintenance. This unit covers PTW essentials, the TEST-PROVE-reTEST method, Lock Out Tag Out, and CVT assessment procedures for EX01–EX04.
Learning Objectives
Define a Permit to Work system and its essential features
State the types of work that require a PTW
Describe the TEST-PROVE-reTEST safe isolation method and explain why each step is essential
Describe Lock Out Tag Out (LOTO) and multi-trade isolation requirements
State the hand-back procedure for PTW closure
Complete a PTW and gas free test certificate for a CVT scenario
14.2 Permit to Work
A Permit to Work (PTW) is a formal documented process controlling work identified as potentially hazardous. It is both a safety management tool and a communication system between installation management, plant supervisors, and those performing the work.
Essential Features
• Clear identification of who may authorise work and who specifies precautions • Training of all personnel in issuing, using, and closing permits • Monitoring and auditing to confirm the system works as intended • Clear identification of types of hazardous work covered • Standardised identification of tasks, risks, permitted duration, simultaneous activities, and control measures
14.2.3 When is a PTW Required?
Work generating heat, sparks, or other potential ignition sources in or near hazardous areas
Breaking containment of flammable, toxic, or pressurised systems
High voltage electrical work or work giving rise to electrical danger
Entry into tanks and confined spaces
Work at height; diving operations; pressure testing
Work affecting evacuation, escape, or rescue systems
Use of portable electrical tools in hazardous areas
Any other potentially high-risk operation
14.4 Safe Isolation — TEST-PROVE-reTEST
Before any work involving opening Ex equipment, all connections including neutral must be safely isolated. The sandwich test:
TEST — Prove the instrument on a known live source: Confirm voltage tester works correctly before testing the isolation. A faulty instrument that reads zero on a live source is detected here.
PROVE — Test the isolation point: Apply the proven instrument to the isolated circuit. Confirm zero volts on all conductors including neutral. Any reading above zero indicates failed or incomplete isolation.
reTEST — Re-prove the instrument on the known live source: Confirm the instrument still gives a live reading after the test. An instrument failure between steps 1 and 2 is detected here.
⚠ Why reTEST is Essential
A voltage tester can fail during use — particularly under high-fault-current conditions. Without the reTEST step, a failure that occurs after step 1 would go undetected — the operator would believe the circuit is dead when it remains live. The sandwich structure confirms the instrument was working both before and after the isolation test.
Lock Out Tag Out (LOTO)
After confirming isolation is complete:
Apply personal padlock to the isolation device — prevents anyone else closing it
Apply warning tag identifying who has isolated and why
Each person working applies their OWN personal padlock — the isolation cannot be released until ALL personal padlocks are removed
No individual may remove another person's padlock
In multi-trade scenarios (electrical + mechanical + instrument), all trades apply their locks simultaneously. The equipment cannot be re-energised until the last lock is removed — each trade is protected independently.
14.2.4 PTW Display and Hand-back
During work, PTW copies must be at:
The work site (or carried by the performing authority if multiple locations)
The central or main control room — so operators know which plant is under permit
The issuing authority or area authority
Hand-back — confirming work completion and PTW closure:
Confirm work is complete (performing authority)
Confirm plant returned to safe condition — isolations removed and verified (responsible authority)
Production staff acknowledge return of plant to their control
PTW formally cancelled/closed — signed and timed by authorised person
Gas Free Test Certificate
A gas-free certificate is required from the assessor (authorised person) before:
Performing the zero voltage check and safe isolation (confirms area safe for instrument use)
Final instrument testing when the installation is re-energised (confirms area remains gas-free for live work)
The gas-free certificate specifies: the candidate name; the specific actions authorised; the bay number; the assessor signature; date and time. It is a specific authorisation — not a blanket clearance for the entire assessment.
Unit 14 Knowledge Check — 10 Questions
CompEx-style questions covering the full unit content.
Q1Unit {num}
What does the reTEST step in TEST-PROVE-reTEST specifically detect?
The reTEST confirms the instrument was working correctly after the actual isolation test. A failure that occurs between step 1 and step 2 would produce a false "dead" reading at step 2. The sandwich structure eliminates this risk.Ref: Safe Isolation
Q2Unit {num}
An isolated motor has one electrical padlock applied. A mechanical engineer arrives to work on the pump. What must happen?
Each trade applies their own personal padlock. Neither can re-energise while the other's lock remains. This protects each trade independently even if communication breaks down.Ref: LOTO
Q3Unit {num}
A PTW is displayed only at the work site and not in the control room. Sufficient?
Control room copy is mandatory. Operators unaware of a live permit could inadvertently operate plant items that are under work — defeating the PTW safety controls.Ref: PTW Display
Q4Unit {num}
When is a gas-free certificate required during CVT EX01?
Two endorsements required: (1) before zero voltage test/isolation; (2) before final instrument testing when installation will be re-energised. Both from the assessor acting as authorised person.Ref: CVT EX01 — Gas Free Certificates
Q5Unit {num}
Correct sequence for returning a motor to service after completing maintenance?
Correct: (1) confirm work complete; (2) obtain de-isolation authorisation from authorised person; (3) remove all locks and tags; (4) confirm de-isolation complete to authorised person; (5) obtain formal PTW closure signed. Removing locks before authorisation is incorrect.Ref: PTW Handback
Q6Unit {num}
What is the significance of including the neutral conductor in safe isolation?
The neutral must always be isolated and confirmed dead. Under fault conditions — a broken neutral elsewhere in the system, a floating neutral in an IT-earthed system, or backfeed from another circuit — the neutral can be live. All conductors must be confirmed dead before work begins.Ref: IEC 60079-17
Q7Unit {num}
A PTW isolation has been issued for a Zone 1 motor for electrical maintenance. What document must be obtained before the zero voltage test is performed?
Before using electrical test instruments (including voltage testers) in a hazardous area, a gas-free certificate must be obtained. The voltage tester itself is a potential ignition source — it must only be used after the area is confirmed gas-free by the authorised person.Ref: CVT PTW / Gas Free Certificate
Q8Unit {num}
What must be confirmed during PTW hand-back before the permit can be closed?
All three confirmations are required before PTW closure. Missing any one leaves ambiguity about equipment status and who is responsible for the plant.Ref: PTW Hand-back Procedure
Q9Unit {num}
What is the minimum PPE specified for CVT assessments?
Section 2 of the CVT PTW specifies minimum PPE: coverall, appropriate footwear (safety boots), hard hat, eye protection, and gloves. PPE is mandatory in the designated training bay areas throughout all CVT assessments.Ref: CVT PTW — Safety Requirements
Q10Unit {num}
A mechanical engineer is working under a PTW isolation when additional electrical work is found necessary. The electrical engineer needs to start immediately. What is the correct process?
A PTW covers specific defined work. Additional work types require either a separate PTW or a formal amendment process depending on the site PTW procedures. In either case, the electrical engineer must apply their own padlock before starting electrical work — ensuring both trades are independently protected on the same isolation.Ref: PTW — Scope and LOTO