Trigger Action Response Plans: What They Are and How They Work

A trigger action response plan (TARP) is a pre-defined set of actions that must be taken when a specific measurable condition is reached. It is not an emergency procedure. It is the step before the emergency — the mechanism that activates a response while there is still time to prevent the worst outcome.

TARPs are common in Australian mining, construction, and heavy industry, particularly for principal hazards where conditions can deteriorate progressively. Ground movement, gas concentration, water inflow, equipment temperature — all of these can be monitored, and a TARP defines exactly what happens when a reading crosses a threshold.

What a TARP Is Required to Define

A TARP has three components. Without all three, it is not a TARP — it is a note.

The trigger condition: A specific, measurable value or observation that activates the plan. “Ground movement exceeding 5mm in 24 hours” is a trigger condition. “Ground looks unstable” is not. The condition must be objective enough that two different people observing the same data reach the same conclusion about whether it has been met.

The action sequence: The specific steps to be taken, in order, by named roles. “Supervisor notifies the shift manager and suspends work in the affected area” is an action sequence. “Take appropriate action” is not. Each step must specify who does what and by when.

The escalation path: What happens if the condition continues to deteriorate, if the initial actions do not stabilise it, or if the condition is met again within a defined period. Most TARPs have two or three levels — a first trigger that suspends non-essential activity, a second that evacuates personnel, a third that initiates emergency response.

What Conditions Qualify as TARP Triggers

Not every hazard condition suits a TARP. The method works where the hazard deteriorates through observable, measurable stages. Where it moves from safe to catastrophic without warning, a TARP cannot provide a useful response window.

Conditions that work well as TARP triggers:

• Ground monitoring readings: Settlement, convergence, or crack displacement exceeding defined thresholds in underground or open-cut workings
• Gas concentration: Methane, carbon monoxide, or hydrogen sulphide levels crossing defined ppm thresholds in underground mines
• Water inflow rates: Volume per unit time in dewatering systems, shaft sumps, or open-cut pit floors
• Rainfall accumulation: Millimetres in a defined period, used for slope stability and surface drainage TARPs
• Equipment parameters: Bearing temperature, oil pressure, hydraulic pressure, or vibration readings outside design tolerances
• Seismic events: Magnitude thresholds from seismic monitoring systems in underground hard rock mining

Each trigger must have a defined measurement method, a defined frequency of measurement, and a defined person responsible for reading and recording the measurement. A trigger that is not measured consistently is a trigger that will not activate when it should.

What the Response Sequence Must Specify

The response sequence is where most TARPs are poorly written. The common failure is specifying the outcome without specifying the action.

“Reduce exposure to the hazard” is an outcome. It does not tell a supervisor what to do, in what order, or by when. When conditions are deteriorating and time is limited, ambiguity in the response sequence produces delays or inconsistent responses.

A well-written response sequence specifies:

• Who: The role responsible for each action — not “the team” but “the shift supervisor”
• What: The specific action — “suspend all work within 50 metres of the affected area and withdraw personnel to the muster point”
• When: The timeframe — “immediately upon confirmation of the trigger condition” or “within 15 minutes of notification”
• Notification: Who must be informed, and through what channel — “notify the mine manager by radio and record the time of notification in the shift log”

The response sequence should be short enough to be followed under pressure. A TARP that requires reading 12 steps while a stope is showing signs of failure will not be followed as written. Three to five clear steps per trigger level is the practical limit.

What Separates a TARP From a Standard Emergency Procedure

Emergency procedures activate after the event. A TARP activates before it.

The distinction matters because the response options are fundamentally different at each stage. Before the MUE, the options include suspension of work, withdrawal of personnel, repair of a failing control, and increased monitoring frequency. After the MUE, the options are emergency response — evacuate, rescue, contain.

A TARP is a preventive control. It sits on the left side of the bowtie diagram — between the threat and the material unwanted event. An emergency procedure sits on the right side — between the event and its consequences.

This is why TARPs are sometimes described as a “last line of defence” before the event. If the TARP fails to prevent the MUE — because the trigger was not recognised, the response was not executed, or the condition deteriorated faster than anticipated — the emergency procedure activates.

Both are necessary. They address different points in the hazard sequence.

Where TARPs Fit in the Critical Control Framework

In critical control management, TARPs often function as critical controls in their own right. For a principal hazard where progressive deterioration is the failure mode — ground instability, water inflow, gas accumulation — the TARP is frequently the barrier that prevents the hazard from reaching its catastrophic consequence.

If the TARP is a critical control, it must be treated as one:

• Performance standard: The trigger conditions are defined, measurable, and documented. The response sequence is specific and assigned to named roles. Personnel are trained and can demonstrate they know the trigger levels and their response obligations.
• Verification: At a defined frequency, someone confirms the TARP is operational — trigger conditions are being measured, records are being kept, and personnel can describe the response without referring to the document.
• Response to failure: If a TARP activation fails — the trigger was met but the response was not executed — that is a critical control failure. It warrants investigation, not just a corrective action note.

A TARP that exists on paper but is not verified, not understood by the personnel responsible for executing it, and not connected to the monitoring system that generates the trigger readings is not a functioning critical control. It is documentation.

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For a breakdown of how RiskSight manages critical controls — including TARP verification schedules and control degradation alerts — see Critical Risk Software for Mining & Heavy Industry.

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