Risk Assessment Fundamentals

Risk Assessment Fundamentals

Risk assessment is the foundation of everything else in ATEX compliance. Before you can classify zones, select equipment, or write an Explosion Protection Document, you need to understand what hazards exist and how significant they are. Article 4 of the Workplace Directive (1999/92/EC) makes this a legal requirement—not an optional best practice.

What Must Be Assessed

The directive specifies that employers must assess explosion risks considering at least four factors:

• Likelihood of explosive atmospheres: How often will explosive atmospheres form, and how long will they persist? This depends on the substances involved, how they're handled, and the ventilation in the area
• Likelihood of ignition sources: What ignition sources could be present—electrical sparks, hot surfaces, static discharge, mechanical sparks, open flames—and could they become active while an explosive atmosphere exists?
• Installations and substances: What processes, equipment, and materials are involved, and how might they interact? The hazard from a small can of solvent differs vastly from a 10,000-litre storage tank
• Scale of effects: If an explosion occurred, what would be the consequences for workers, the facility, and the surrounding area?

Importantly, the directive states that explosion risks must be assessed "overall"—you can't look at individual elements in isolation. A source that seems low-risk on its own might become high-risk when combined with other factors.

Identifying Flammable Substances

The starting point is identifying every flammable substance present or potentially present in the workplace. This includes process materials (raw materials, intermediates, products), cleaning agents and solvents, by-products and waste streams, and maintenance materials. Don't forget substances that are only present occasionally—cleaning fluids used once a week, solvents used during maintenance shutdowns, or materials from adjacent processes that could migrate through openings.

For each substance, you need its flammable properties: flash point, auto-ignition temperature, lower and upper explosive limits (LEL/UEL), vapour density, and—for dusts—minimum ignition temperature and energy. Safety data sheets are the primary source, but they don't always contain all the explosion-relevant data you need.

Identifying Release Sources

Next, determine where and how flammable substances could be released into the atmosphere. Release sources are classified by grade: continuous (releasing constantly or for long periods), primary (expected to release periodically during normal operation), and secondary (not expected during normal operation, and if it occurs, only for short periods). This classification directly feeds into zone classification.

Typical release sources include pump seals, valve packings, flanged pipe connections, tank vents, sampling points, loading and unloading operations, and equipment openings during maintenance.

Identifying Ignition Sources

The EC ATEX Guidelines identify 13 potential ignition sources that must be considered: hot surfaces, flames and hot gases, mechanically generated sparks, electrical equipment, stray currents and cathodic corrosion protection, static electricity, lightning, electromagnetic waves, ionising radiation, ultrasonics, adiabatic compression and shock waves, exothermic reactions, and self-igniting dusts. Not all will be relevant at every site, but each must be systematically considered and either eliminated or controlled.

Connected Areas

One commonly overlooked requirement: places that are or can be connected via openings to places where explosive atmospheres may occur must be included in the assessment. A "safe" area connected by a doorway, pipe penetration, or ventilation duct to a hazardous area isn't automatically safe—gas or dust can migrate through openings, and the assessment must account for this.

When to Reassess

Risk assessment isn't a one-time activity. The directive requires review whenever the workplace, work equipment, or organisation of work undergoes significant changes. A new process, a relocated vessel, a different raw material, a changed operating procedure—any of these could invalidate previous assessments. Changes should trigger specific questions: does this affect where explosive atmospheres might form? Does it introduce new ignition sources? Does it change the consequences of an incident?

Competence

Risk assessment should be carried out by people who understand both the process being assessed and the principles of explosion protection. This often means combining process knowledge from operations staff with explosion safety expertise from specialists. The employer is responsible for ensuring the assessment is competent and complete—getting it wrong at this stage means everything built on it, from zone classification to equipment selection, will be wrong too.