Spill risks at work

Before you can prevent spills, you need to know where they are likely to happen. Most workplaces have a handful of activities that cause nearly all their spills: transferring liquids, storing containers, maintaining equipment, washing vehicles and floors, and receiving deliveries. A spill risk assessment walks through the site, lists each place where liquids are stored or moved, and asks three questions about each one. What could escape? How much, and how fast? Where would it go?

Where spills come from

Transfer is the riskiest activity at most sites. Every time a liquid moves from one container to another, it can overflow, splash, leak from a hose or fitting, or go into the wrong place. Fueling vehicles and equipment, filling day tanks, decanting chemicals into smaller containers, pumping out sumps and loading tanker trucks all involve transfer. Overfills during fuel deliveries are a classic cause of large spills: the driver pumps more than the tank can hold, often because a gauge is wrong or the overfill alarm has been disabled.

Storage is the next big source. Drums and totes get punctured by forklifts, corrode from the outside, or split when frozen. Tanks leak from corroded bottoms, failed welds or loose fittings. Containers stored outdoors fill with rainwater and overflow. Incompatible chemicals stored together can react if one leaks. Lesson 4 covers safe storage in detail, and HSE-312 covers chemical storage and compatibility more fully.

Equipment is a constant source of small spills. Hydraulic hoses burst on excavators, loaders and lifts. Engines and transmissions drip oil and coolant. Gearboxes leak. Compressors drain oily condensate. Mobile equipment working near water, such as on bridges, docks and shorelines, is a particular concern because even a small hose failure can put oil straight into a waterway.

Washing and cleaning move contaminants with water. Vehicle wash bays send oil, detergent and road grime to drains. Floor washing in shops can flush spilled oil and metal fines into sewers. Equipment cleaning with solvents creates waste that must be collected. Concrete truck washout is highly alkaline and harmful to fish if it reaches a stream.

Thinking in terms of source, pathway and receptor

Environmental professionals use a simple model: source, pathway, receptor. The source is where the substance could escape. The pathway is how it would travel: across pavement, into a floor drain, into a storm drain, into soil, through groundwater or through the air as vapor. The receptor is what could be harmed: a worker, a neighbor, a creek, a wetland, a drinking water well, a sewage treatment plant. If any one of the three is missing, there is no risk to that receptor. Prevention works by controlling the source, cutting the pathway or protecting the receptor.

A drum of oil stored on a spill pallet inside a building with no floor drains has a source but almost no pathway. The same drum on gravel beside a ditch has a short pathway to a creek. A fuel tank uphill from a drinking water well has a pathway through soil and groundwater to a receptor that people depend on. Mapping these chains is the heart of a good spill risk assessment.

Knowing your drains

Drains are the most important pathways at most sites, and many workers do not know where they go. Buildings and yards usually have two separate systems. Sanitary sewers carry wastewater from toilets, sinks and some process drains to a sewage treatment plant. Storm sewers carry rainwater from roofs, parking lots and roads, usually without any treatment, straight to the nearest creek, river, lake or ditch. Some older cities have combined sewers that carry both and overflow into rivers in heavy rain.

Pouring oil into a storm drain is essentially pouring it into a creek. Pouring it into a sanitary sewer is not much better: sewage plants are not designed to treat fuels, solvents and many chemicals, and municipal sewer-use bylaws prohibit discharging them. Floor drains in older shops are sometimes connected to storm sewers by mistake, or to dry wells that drain straight into the ground. Every site should have a drain map that shows where each drain goes, and drains near spill risks should be clearly labeled, for example with a painted marking that says the drain leads to a creek.

Rating spill risks

Once the sources are listed, it helps to rate them so that effort goes where it matters most. A simple method multiplies a likelihood score by a consequence score. Likelihood reflects how often the activity happens, how reliable the equipment is and whether there have been past spills. Consequence reflects the volume that could escape, how hazardous the substance is and how short the pathway to a sensitive receptor is. The highest scores get attention first.

# A simple spill risk ranking: likelihood (1-5) x consequence (1-5). Illustrative site.
sources = [
    ("Fuel delivery to main tank",     3, 5),
    ("Drum storage on gravel by ditch", 4, 4),
    ("Excavator working at riverbank",  3, 5),
    ("Parts washer near floor drain",   3, 3),
    ("Battery shelf in shop",           2, 3),
    ("Antifreeze top-ups in yard",      4, 2),
]
ranked = sorted(sources, key=lambda s: s[1] * s[2], reverse=True)
for name, like, cons in ranked:
    score = like * cons
    level = "high" if score >= 15 else "medium" if score >= 8 else "low"
    print(f"{name:<34} L{like} x C{cons} = {score:>2}  {level}")

Drum storage on gravel by ditch    L4 x C4 = 16  high
Fuel delivery to main tank         L3 x C5 = 15  high
Excavator working at riverbank     L3 x C5 = 15  high
Parts washer near floor drain      L3 x C3 =  9  medium
Antifreeze top-ups in yard         L4 x C2 =  8  medium
Battery shelf in shop              L2 x C3 =  6  low

The numbers in such a ranking are judgments, not measurements, and two people may score the same source differently. The value lies in the discussion: walking the site together, agreeing on what could go wrong, and producing a short list of the places that need better containment, procedures or spill kits.

Human factors

Equipment fails, but people cause or worsen most spills. Common human factors include rushing, leaving a transfer unattended, skipping a pre-use inspection, using the wrong container, overfilling because a gauge was not checked, disabling an alarm that kept going off, and not reporting a small leak because it seemed unimportant. Fatigue, poor lighting, unclear labels and confusing valve arrangements make errors more likely.

Good design and procedures make the safe action the easy action. Fill pipes are labeled with the product they take, so diesel cannot easily go into the gasoline tank. Automatic shut-off nozzles stop flow when a container is full. Transfers are never left unattended. Valves are locked when not in use. Workers are encouraged, not blamed, when they report small leaks and near misses, because those reports reveal problems before they cause a large spill.

Seasonal and site-specific risks

Weather changes spill risks. Spring thaw and heavy rain overload containment areas and wash spills off pavement. Freezing splits containers and hoses and can crack tanks if water collects inside. Hot weather increases vapor from fuels and solvents and can make sealed containers bulge. Floods can lift tanks off their foundations and carry drums away. A spill risk assessment should consider what happens in each season, not just on a dry summer day.

Some sites have special risks. Farms handle large volumes of fuel, fertilizer, pesticides and manure, often near wells and streams. Construction sites move fuel to temporary tanks and equipment that work near watercourses. Laboratories store many small containers of different chemicals. Marinas fuel boats over water. Fuel stations, covered in HSE-351, handle large volumes of gasoline and diesel with frequent transfers by the public. Each needs a risk assessment that fits its activities.