0. JSA Risk Assessment Preview: Underground Tunnel Blasting and Drilling Operations

1. On-Site Incident & Hazard Analysis

A. [Hypothetical Sample Case] Unexpected Detonation During Drilling Due to Striking a Misfire (Socket)

Note: The following is an illustrative, hypothetical incident designed solely for risk assessment training.

During the excavation of a deep mountain rail tunnel in the Scottish Highlands, a night shift crew was conducting drilling operations for the next blast cycle. A portion of the rock face contained a "socket"—the remnant of a borehole from the previous blast that still contained unexploded gelignite and a live detonator. To accelerate the programme, the crew bypassed the mandatory high-pressure washdown and visual inspection of the face. The drilling jumbo operator began advancing the drill bit according to the pre-marked pattern.

As the rotating drill bit directly struck the live detonator hidden in the socket, the residual explosive immediately detonated. The sudden, localised explosion in the confined heading obliterated the drilling jumbo's boom. Flyrock shattered the operator's cab glass, instantly killing the operator and a surveyor who was standing nearby checking the alignment. The Health and Safety Executive (HSE) investigation cited gross breaches of the Explosives Regulations 2014 (ER 2014) and BS 6164 standards. This hypothetical scenario starkly illustrates that washing down the face and inspecting for misfires is an absolute, non-negotiable lifeline. Drilling blindly without this check is essentially equivalent to striking a detonator with a hammer.

B. Structural, Mechanical, and Regulatory Hazard Mechanisms

Underground tunnel blasting is a maximum-risk engineering operation that uses immense chemical explosive energy to mechanically fracture rock. The most catastrophic hazard in this process is "premature detonation" or striking unexploded ordnance (sockets/misfires). During jumbo drilling, the primary physical mechanism of disaster is the drill bit intersecting residual explosive energy from a previous blast cycle. To prevent this, washing down the face with high-pressure water and thoroughly inspecting for remnants of old boreholes is a mandatory control before any drilling commences.

During the explosives charging phase, micro-electrical energy such as static electricity, lightning, or stray Radio Frequency (RF) currents can easily trigger sensitive electric detonators. Static from worker clothing, improper earthing of excavation plant, or even the transmission energy from a handheld radio can induce a fatal current. Immediately following a blast, the chemical reaction of the explosives leaves a highly toxic cloud of carbon monoxide, nitrogen dioxide, and other noxious gases trapped in the heading. Entering this zone without prior mechanical air displacement and quantitative gas testing by a Competent Person directly results in mass asphyxiation fatalities.

🚨 UK Statutory Regulations & Safety Standards (HSE, BS 6164 & ER 2014)

Explosives Regulations 2014 (ER 2014): Mandates that any operation involving explosives must be strictly controlled to prevent accidental initiation. Charging must be done carefully using non-sparking stemming rods, and RF transmitters (mobile phones, radios) must be excluded from the blast area.

BS 6164 (Code of practice for health and safety in tunnelling): Explicitly prohibits drilling into or near any socket (remnant hole) from a previous blast to prevent striking misfired explosives. It also requires the rock face to be washed down and inspected before drilling.

Control of Substances Hazardous to Health Regulations 2002 (COSHH): Requires exposure to toxic blast fumes (CO, NOx) and Respirable Crystalline Silica (RCS) to be adequately controlled through forced ventilation and strict re-entry procedures.

Construction (Design and Management) Regulations 2015 (CDM 2015): Requires that the Principal Contractor ensures a Safe System of Work (SSoW) is in place for all blasting operations, including appointing a competent Shotfirer and establishing secure exclusion zones.

2. Standard Data Entry Guide for Smart JSA Bridge

To ensure the Smart JSA Bridge platform generates safety control measures fully compliant with UK HSE guidelines and BS 6164 standards, enter the following standardised job steps into the system:

• [Step 1] Face Surveying and Drill Pattern Marking

  • Detailed Description: Mandate mechanised scaling prior to marking; utilise MEWPs; physically separate surveyors from tramming heavy plant using banksmen.

• [Step 2] Drilling Jumbo Tramming and Setup

  • Detailed Description: Deploy dedicated banksmen for movement; verify backup alarms; inspect outrigger stability and check hydraulic lines for leaks.

• [Step 3] Face Drilling Operations

  • Detailed Description: Wash down the face and visually inspect for sockets (misfires); activate LEV; mandate face-fit tested respirators and hearing protection.

• [Step 4] Explosives Transport and Charging

  • Detailed Description: Wear anti-static PPE; turn off all two-way radios and mobile phones (RF hazard); use only wooden stemming rods; do not force explosives.

• [Step 5] Blast Circuit Wiring and Firing

  • Detailed Description: Shotfirer tests the circuit with an approved ohmmeter; sound warning sirens; physically verify complete evacuation beyond the safety radius.

• [Step 6] Post-Blast Ventilation and Gas Testing

  • Detailed Description: Operate forced ventilation fans; a Competent Person must measure O2 and toxic gases (CO, NOx) before granting re-entry clearance.

3. Recommended Final JSA Document (Database Sample)

Below is the final JSA document generated based on automated system recommendations and adapted for UK civil tunnelling and explosive engineering standards:

4. JSA Engineering Mechanism for Tunnelling: Explosives and Toxic Gas Control

Underground tunnel blasting and drilling are maximum-risk operations that directly handle the explosive energy of blasting agents alongside the persistent threats of ground collapse and gas poisoning. Vague instructions such as "be careful with explosives" or "don't breathe the gas" are entirely inadequate for HSE compliance audits and fail to prevent mass-casualty events in confined headings.

Smart JSA Bridge utilises an automated risk analysis algorithm calibrated against the Explosives Regulations 2014 (ER 2014), BS 6164 (Tunnelling Safety), and COSHH standards to deliver real-time, actionable hazard controls.

By inputting 6 structured job steps, the algorithm calculates required technical controls—including mandatory washdown and inspection protocols to prevent striking sockets, strict RF and static electricity control zones to prevent premature detonation, absolute safe clearance radii for personnel protection from blast overpressure, and specific ventilation timing and gas testing parameters for re-entry.

Principal Contractors, Appointed Shotfirers, and Tunnel Site Managers can customise these parameters with a single click to match specific geological conditions and explosive load designs across UK tunnel construction projects.

Streamline your safety documentation workflow while ensuring total statutory compliance for high-risk blasting operations. Generate your customised risk assessment today.

👉 Enter job steps on Smart JSA Bridge and generate your custom JSA (smartjsabridge.com)