Spark, Fire and Explosion Control

Chapter objectives

After this chapter, the reader should be able to:

• distinguish fire conditions from dust-explosion conditions;
• identify abrasive-process ignition sources and potential fuels;
• map the complete travel path of sparks, hot particles and heat;
• decide whether work should be eliminated, relocated or controlled as hot work;
• prepare an area and protect adjacent levels, cavities and equipment;
• control grinding and cutting on tanks, drums, pipes and enclosed sections;
• recognise when dust may be combustible or reactive;
• explain how accumulated layers can support a secondary explosion;
• separate incompatible dusts and processes;
• coordinate extraction, collectors and spark control;
• use suitable housekeeping without re-suspending dust;
• apply fire-watch, close-out and restart controls;
• recognise conditions requiring an immediate controlled stop; and
• troubleshoot fire and explosion hazards systematically.

Fire requires fuel, oxygen and a sufficiently energetic ignition source. A dust explosion additionally requires combustible particles dispersed in air within a hazardous range and sufficient confinement for pressure to develop. Removing any required element interrupts the event.

The absence of a visible cloud does not prove that dust deposits are harmless. A layer can burn, conceal hot material or become dispersed by an initial fire, pressure wave, cleaning jet or equipment failure.

Visible grinding sparks are only one ignition source. Inspect the whole process for:

• incandescent particles, hot swarf and cut-off fragments;
• hot workpieces, sharp offcuts and recently ground edges;
• friction from binding, rubbing, poor tracking or seized components;
• overheated bearings, motors, brakes, drives and cables;
• damaged electrical equipment, loose connections and arcing;
• static discharge from powders, hoses, filters, containers or clothing;
• welding, gouging, flame cutting, brazing and soldering nearby;
• smoking, open flames, heaters and vehicle exhausts;
• chemical reaction, self-heating or contaminated waste; and
• hot particles transported through extraction ducting.

Abnormal heat, odour, smoke, colour change, noise or vibration is a warning condition. Stop and investigate rather than increasing airflow, contact force or production speed to continue the task.

Sparks rarely stop where they first land. They can bounce from floors, pass through grating, enter cable trenches, settle behind machines, lodge in insulation, travel inside hollow sections or be pulled into extraction.

Observe the process from first contact to shutdown and ask:

1. What direction does the wheel or belt throw particles?
2. How does the direction change as the tool or workpiece moves?
3. Can sparks fall through openings or reach another floor?
4. Are there hidden cavities, wall penetrations, roof spaces or combustible linings?
5. Can extraction carry hot particles to ducts, filters or collectors?
6. Can wind, fans or vehicle movement extend the travel path?
7. Where will hot offcuts and spent abrasives be placed?
8. What could smoulder after visible work ends?

Inspect the opposite side of partitions, floors and workpieces where heat may conduct through. Spark screens should contain and direct particles toward a controlled landing area without trapping heat, blocking ventilation, obstructing escape or creating rebound toward the operator.

Treat grinding, abrasive cutting and any other process that produces sparks or significant heat as hot work wherever combustible, flammable or explosive material may be affected. A designated grinding bay can simplify control, but designation alone does not make it safe when fuel, dust or process conditions change.

Use this decision sequence:

1. Eliminate: Can the part be replaced, unbolted, mechanically separated or repaired without ignition-producing work?
2. Relocate: Can the item be moved to a prepared hot-work area away from fuel and occupied operations?
3. Isolate: Can connected equipment, lines, energy, material flow and hazardous atmosphere be positively controlled?
4. Prepare: Can combustibles, residues and dust be removed or protected and receiving areas inspected?
5. Authorise: Does the site hot-work system release the defined task, location, time, personnel and precautions?
6. Monitor: Are fire watch, communication, alarm, extinguishing readiness and post-work inspection established?

If the task changes location, material, tool, duration, atmosphere, collector connection or spark direction, return to the decision point. Do not extend an authorisation by assumption.

Keep the work zone orderly. Hoses, leads, screens and extinguishing equipment should remain accessible without crossing escape routes or creating trip hazards.

Flammable material may be present in containers, process equipment, drains, pits, coatings, cleaning stations, fuel systems, aerosols or nearby storage. Vapours can travel away from a leak or open container and ignite at the hot-work location.

Before work:

• identify products, residues and decomposition hazards;
• stop transfer, spraying, cleaning and dispensing that can release vapour;
• close, remove or isolate portable containers;
• prevent leakage from connected pipes, valves and equipment;
• control low points, drains and enclosed spaces where vapour may collect;
• use suitable atmospheric testing where the assessment requires it;
• maintain ventilation without spreading vapour toward ignition; and
• prevent reintroduction while hot work and close-out remain active.

Oxygen enrichment increases the ease and intensity of combustion. Keep oxygen equipment, hoses and fittings clean and suitable for oxygen service, protect them from sparks and oil contamination, and never use oxygen for ventilation, cooling or blowing dust from clothing or equipment.

Drums, tanks, vessels, pipes, ducts and hollow sections can retain flammable vapour, combustible residue or pressure after appearing empty. Rinsing, leaving a lid open or waiting several days does not by itself establish safe conditions.

HSE identifies grinding and disc cutting as hot work capable of igniting residues in drums and containers, including materials such as oils, solvents and fuels. [S323] Use cold cutting or dismantling methods wherever they remove the ignition hazard.

Many finely divided materials can burn even when the bulk material appears difficult to ignite. Relevant materials may include aluminium, magnesium, titanium and other metals; polymer, paint and coating dust; wood, textile or organic material; polishing lint and compound; and mixed process residues.

Combustibility cannot be decided reliably from:

• whether the parent metal normally burns;
• spark colour or quantity;
• particle colour or visible fineness;
• a previous job that did not ignite;
• the absence of a warning on an unrelated product; or
• an ordinary dust-extraction rating.

ISO/IEC 80079-20-2 specifies test methods for identifying combustible dust and dust-layer characteristics used in hazardous-area and equipment decisions. [S321] Material identity, process history, representative testing and competent engineering determine the required controls.

A primary event may begin inside a machine, enclosure, duct or collector. The pressure wave can disturb deposits on beams, lights, cable trays, roofs and equipment, creating a larger secondary cloud. Ignition of that cloud can produce a more destructive secondary explosion.

DOSH’s motorcycle-rim manufacturing alert describes a polishing-machine fire followed by a chain of dust explosions and highlights dust control, ignition-source control and explosion-damage control. [S319]

Prevent escalation by:

• containing dust release at the process;
• preventing deposits on horizontal and elevated surfaces;
• inspecting concealed and difficult-to-reach areas;
• keeping collectors and ducts suitable and maintained;
• avoiding work that disperses accumulated dust;
• controlling ignition throughout the connected system; and
• providing engineered fire and explosion protection where the assessment requires it.

Do not wait for a thick visible layer. The significance of a deposit depends on the material, area, process and potential for dispersion.

Mixing dusts can change combustibility, reactivity, waste classification and extinguishing strategy. Keep collection routes separately assessed where processes involve:

• different combustible metals;
• metal and organic or polymer dust;
• reactive metal and water or aqueous slurry;
• iron or steel sparks entering a light-metal dust system;
• oil-, solvent- or compound-contaminated dust;
• oxidising materials; or
• residues with unknown composition.

Use dedicated tools, extraction, containers and cleaning equipment where cross-contamination would create a hazard.

Label waste by source and prevent hot material entering the receptacle. A container suitable for ordinary steel swarf may be unsuitable for fine reactive metal dust.

When an exact abrasive, collector, filter, container or extinguishing-system value is required, Refer to the product label, Technical Data Sheet, or MKTECH representative.

Good application control reduces unnecessary heat and erratic particle throw:

• select the correct tool and abrasive type for the material and operation;
• keep the guard installed and correctly positioned;
• mount the abrasive with clean, compatible components;
• secure the workpiece and support offcuts;
• maintain a stable contact angle and controlled entry;
• avoid binding, twisting, side loading and excessive force;
• replace damaged, loaded, glazed or inefficient abrasives;
• maintain bearings, belts, contact wheels and drives; and
• allow hot workpieces and offcuts to cool in a controlled non-combustible location.

A spark-reduction measure must not weaken guard coverage, cause tool overload, reduce visibility or direct fragments toward people. Wet methods require full compatibility with the abrasive, electrical tool, workpiece, reactive dust and waste system.

Local extraction can control airborne dust while also transporting hot particles and combustible material into a confined system. Ordinary capture performance does not establish fire or explosion suitability.

Do not connect a new polishing, sanding or metal-grinding process to an existing collector because the hose fits. Review material, spark loading, dust properties, branch balance, collector location, protection systems and waste route before change.

Housekeeping is an explosion-control measure when it removes deposits without dispersing them.

Use a planned method that:

• captures dust at the source before it settles;
• defines accessible and elevated inspection areas;
• uses equipment documented as suitable for the material and hazardous area;
• isolates production where cleaning can disturb deposits;
• avoids dry sweeping or uncontrolled compressed air;
• prevents dust falling from one level onto workers or ignition sources;
• keeps incompatible dusts and cleaning equipment separate;
• empties collectors and vacuums before overfilling;
• contains filters, bags and waste during change; and
• records recurring deposits as a control fault to correct.

Do not clean a large area by blowing dust toward extraction. The resulting cloud may reach ignition sources, penetrate inaccessible spaces and overload the collector. DOSH guidance on chemical-processing dust events specifically discourages compressed-air blowing and sweeping in favour of suitable industrial vacuum cleaning. [S320]

A hot-work permit or equivalent release coordinates the conditions that must remain true during the job. It should identify:

1. exact task, item and location;
2. authorised time window and shift handover;
3. materials, residues and connected processes;
4. isolation and atmosphere-control method;
5. combustible removal and protection;
6. spark, heat and extraction controls;
7. fire watch and receiving-area coverage;
8. alarm, communication and emergency actions;
9. close-out inspection and monitoring period; and
10. responsible persons for release, suspension and closure.

The release ends when conditions change, the time expires, the work moves or control is lost. Suspend the job and issue a fresh release after reassessment. A signature does not compensate for an unprepared area or an uncontrolled dust hazard.

The fire watch monitors areas the operator cannot continuously observe, including adjacent rooms, reverse sides, lower levels, penetrations and extraction receiving points. The person must understand the task hazards and have authority to stop work.

The fire watch should:

• confirm the prepared boundary before ignition-producing work;
• maintain communication with the operator and permit controller;
• watch spark travel, hot surfaces, smoke, odour and changing conditions;
• keep access and escape routes clear;
• know how to raise the alarm and initiate evacuation;
• use available response equipment only within training and the emergency plan;
• continue post-work monitoring for the defined period; and
• record closure or escalate any abnormal condition.

DOSH confined-space guidance emphasises combustible removal, suitable protection and a trained fire watch for hot work within confined spaces. [S322] Apply the same disciplined observation principle wherever hidden or delayed ignition is credible.

Different fuels and reactive materials require different response methods. Water, foam, carbon dioxide, dry chemical or specialised media may be effective for some hazards and dangerous or ineffective for others. Selection must follow the identified material, equipment, atmosphere and facility emergency plan.

Before release, confirm:

• alarm method and who receives it;
• emergency isolation and shutdown points;
• evacuation route and assembly arrangements;
• suitable response equipment and trained users;
• restrictions for reactive metal, electrical or confined-space hazards;
• access for emergency services;
• control of smoke and contaminated run-off; and
• preservation of the scene after people are safe.

If fire enters a collector, duct, container or enclosed machine, do not open it casually. Opening can admit oxygen, release flame, disperse dust or expose the person to pressure and toxic products.

Stopping the tool does not close the fire risk. At completion:

• remove hot offcuts, spent abrasives and waste to controlled locations;
• inspect the immediate area and full spark-travel path;
• inspect reverse sides, cavities, lower levels and penetrations;
• check extraction, ducts, collectors and waste containers for abnormal heat or smoke;
• verify that temporary screens and covers did not conceal ignition;
• restore fire detection or suppression systems that were controlled for the task;
• maintain fire watch for the assessed post-work period;
• record findings and close the hot-work release; and
• hand over unresolved conditions to the next responsible person.

Thermal imaging can support inspection where suitable, but it does not replace physical access, material knowledge or continued observation. A surface temperature image may not reveal a concealed ember behind insulation or inside a duct.

Stop grinding, cutting, sanding or polishing when:

• unidentified combustible, flammable or reactive material is found;
• spark travel extends beyond the prepared and monitored boundary;
• a screen, cover, extraction control or isolation is displaced;
• smoke, flame, smouldering, unusual odour or abnormal heat appears;
• dust becomes visibly dispersed or deposits are disturbed;
• a collector, duct, filter or waste container becomes hot, damaged or abnormal;
• incompatible material enters the collection or waste route;
• atmosphere monitoring, ventilation or required fire watch is lost;
• a used container, pipe or enclosed section is not under a documented release;
• work conditions no longer match the hot-work authorisation;
• emergency equipment, alarm or escape route becomes unavailable; or
• the operator cannot identify where sparks and hot material are landing.

Isolate the task as required, raise the alarm when indicated, control access and follow the site emergency plan. Do not restart until the cause is understood, controls are restored and the complete area has been released again.

Investigate from fuel and ignition source through dispersion, confinement, extraction, work practice and emergency readiness. Correct the system cause rather than relying on a larger screen, more PPE or more frequent cleanup alone.

Before ignition-producing work begins, confirm:

• [ ] the exact task, workpiece, material and location are identified;
• [ ] elimination, cold methods and relocation have been considered;
• [ ] ignition sources and fuels are mapped through the complete work cycle;
• [ ] the full spark, bounce, fall-through and extraction path is controlled;
• [ ] combustibles, flammable materials, residues and dust deposits are removed or protected;
• [ ] containers, pipes, ducts and enclosed sections are prepared and isolated through the site system;
• [ ] atmosphere and ventilation controls match the assessed hazard;
• [ ] the abrasive, tool, guard, support and technique minimise unnecessary heat and spark spread;
• [ ] extraction and collectors are suitable for the material and hot-particle exposure;
• [ ] incompatible or reactive dusts have separate collection and waste routes;
• [ ] housekeeping will remove dust without dispersing it;
• [ ] the hot-work release defines task, boundary, time and responsible persons;
• [ ] fire watch covers hidden, adjacent and lower receiving areas;
• [ ] alarm, isolation, evacuation and suitable response equipment are ready;
• [ ] post-work monitoring and handover are defined; and
• [ ] everyone understands the stop-work conditions.