Anyone who has worked in a high-risk environment has probably heard the terms ISSOW, COW and PTW - like many terms used in industry it's easy to just carry on with your day job without really thinking much about how similar (or different) these are.
In this post I'll give a brief definition of each term and we'll look at how it's getting harder to tell at least two of them apart!
ISSOW stands for 'Integrated Safe System of Work'
It's a digital platform that combines:
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Risk assessments
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Isolation management
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Task planning and templates
The key word here is 'combine' - rather than having to switch between multiple systems to access the various components you need, ISSOW should have them all readily available in the same package. Having an ISSOW in place should reduce paperwork, improve efficiency and minimise error - which should all lead to improved safety.
PTW: The Core Component
Permit to Work (PTW) is the foundation that ISSOW builds on. It’s the formalised process that ensures hazardous work:
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is clearly defined
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is properly risk-assessed
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is authorised before the task can commence
Traditionally, PTW was a paper-based system. Paper forms would capture task details and a manual sign-off w0uld allow work to proceed.
Now, most sites are moving toward electronic Permit to Work (ePTW) systems—and that’s where the lines with ISSOW start to blur.
Modern PTW: Now With Risk and Isolation Features
Many modern Permit to Work systems have evolved to include:
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Built-in risk assessment tools
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Isolation tagging and management
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Integrated SIMOPS handling
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Digital signatures and audit trails
In other words, they’re looking a lot like ISSOW.
The terms do appear to be becoming interchangeable - when we talk to potential customers most of them use the term 'Permit to Work' to find us, and we hardly every encounter the term ISSOW - this is likely because it's very clear at an early stage that our system basically does at least everything that traditional ISSOW does (and more)!
Control of Work (CoW): The Bigger Picture
Control of Work is the overarching framework that both PTW and ISSOW fit inside. It’s not a single system—it’s a coordinated approach to managing:
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Permits
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Isolations
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Risk assessments
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SIMOPS
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Work scheduling
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Personnel tracking
- And any other activity which could affect site safety
It’s how a site maintains situational awareness and avoids conflict—especially during high-risk or simultaneous operations. CoW could be a combination of different systems, paper based and digital.
In Summary
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PTW is the core process for authorising high-risk work, and many modern systems include Risk and Isolations management
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ISSOW is a digital system that integrates PTW with risk and isolation management.
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Control of Work is the strategy and structure behind them both.
In many cases today, PTW and ISSOW are almost interchangeable—because ISSOW and PTW often share the same functionality.