Dangerous Places

DANGEROUS PLACES

By Dwayne Jenkins and Larry Christensen

Many workplaces hold a hidden, deadly hazard. The first step in protecting workers is understanding confined spaces -- and the dangers awaiting workers who enter them.

Many well-diggers in early times had a strange ritual that puzzled and bemused their onlookers. At the start of work in the morning, they would lower a large bucket into the well, crank it back up and then empty the seemingly already empty container. They would repeat this bizarre spectacle 20 or 30 times, causing spectators to question their sanity. There was clearly nothing in the bucket. They hadn’t hit water yet. But it was not a superstitious ritual to magically draw water into the well, as many onlookers suspected. It was actually designed to bail out the stale air in the excavation and replace it with fresh air for the day’s work. The well diggers had found by long experience passed down in their trade that "empty" buckets are a lot easier to pull up from the depths than are unconscious well diggers.

Coal miners in the days before battery powered lamps used an acetylene flame burning in a reflector lamp on their helmets. They also carried another flame that they would carefully adjust to a mark on a ruler in the lamp. They would check its height occasionally while they worked. If the air was getting "bad", the flame would be under the mark. If the flame would suddenly go out, they knew they had hit a pocket of "coal damp" -- carbon dioxide. If the flame got larger, they knew they were encountering "fire damp" (methane gas). They didn’t need the lamp to detect "stink damp" -- hydrogen sulphide -- because the could smell it (or watch the canary fall from its perch). Watching the lamp saved a lot of miners from fires and asphyxiation, and the system improved when the "Davie’s Safety Lamp" was invented. It had a fine copper mesh screen around the burner to cool the flame and keep it from igniting flammable gas if it was present above the lower explosive limit.

These examples illustrate a class of hazards associated with work in "confined spaces". While the provinces (and the federal jurisdiction) have slightly different definitions of the term "confined space", Alberta’s is fairly typical: "A confined space means an enclosed or partially enclosed space having restricted access and egress and which, due to its design, construction, location, atmosphere, the materials or substances in it or other conditions, is or may become hazardous to a worker entering it, or does not have an easy means of escape for, or rescue of, a worker entering it."

Confined spaces come in every shape, size and configuration imaginable. Often, much of the risk to workers stems from the fact that they do not recognize a space they are about to enter as a confined space. Almost any space having any of the characteristics described in the regulation quoted above may be -- or become -- a confined space. Common examples include the following:

* tanks, tank cars, tanker trucks;

* vats, drums, bins and silos;

* boilers, mixing tanks and reactor vessels;

* degreasers, digesters and boilers;

* sumps, cellars, drained pools or reservoirs;

* sewers, tunnels and pipelines;

* transformers and utility vaults;

* caves, mines and excavations;

* truck boxes and shipping containers,

* ducts, tunnels, and pipes; and

* sealed rooms, closets and storage areas.

Confined spaces are not intended for human occupancy. They are not sites of ongoing or regular work activity. They are usually entered only for such purposes as cleaning, inspection, maintenance, repair or construction. And they don’t normally have doors.

Confined spaces tend to have limited means of entry and exit. Entry points may not be designed for easy walk-in. Other limitations include access by ladders or by stairways that provide poor access because of restrictive slope, narrow width or extreme length. Physical obstructions such as bulkheads, collapsed material, or machinery may impede exit. Limited means of entry and exit not only makes escape or rescue difficult, but it can also restrict natural ventilation.

Confined spaces have poor natural ventilation with the presence of, or potential for, a dangerous atmosphere, or a "confined atmosphere" to exist or develop. Poor ventilation can be the result of unpredictable or limited air movement, or natural currents that could draw contaminated air into the space. The most common cause of a confined atmosphere is physical enclosure on all sides. However, vats, pits and vessels that contain confined atmospheres may be open on one face -- the top. In these cases, the confined atmosphere may result from the entry of a gas that is heavier than air; the release of a gas from the disturbance of wastes at the bottom of the space; or the existence of a temperature inversion above the space that prevents the movement of air through it. Even vessels less than 1.5 metres deep may have poor natural ventilation.

Sometimes, an area that is not normally a confined space may become one under special circumstances. An electrical room after a fire is one good example: Oxygen has been consumed by the burning process, smoke and other combustion products may have built up, and the normal ventilation, often by means of forced air through ductwork, may have been completely or partially cut off by the lack of electrical power. Workers entering the room to assess damage or begin cleanup must treat it as a confined space.

Workers continue to die of the same old hazards in confined spaces for the same old reasons:

* They do not recognize the space they are about to enter as a confined space. As a result, they do not recognize the danger and do not take the necessary precautions.

* They trust their senses. They think that if a space looks safe, feels, smells and sounds safe, it must be safe. In fact, almost all hazardous atmospheres are invisible, tasteless and odorless.

* They underestimate the danger. Even if they are aware of a real or potential hazard, they think they can get in and out before they are affected. They do not realize how quickly they can be overcome by a hazardous atmosphere.

* They do not stay on guard while in the confined space. They forget that a hazard may develop after they have entered the space.

* They try to rescue other people who have been overcome in a confined space. (Sixty per cent of all fatalities in confined spaces are would-be rescuers who are themselves overcome while attempting to aid a co-worker in trouble.) The sad fact is that untrained and unequipped rescuers often die along with the victim they are trying to save.

HAZARDS

Many different hazards may exist in confined spaces.

Lack of oxygen. Air normally contains approximately 20.9 per cent oxygen, and people need a concentration of at least 18 per cent to be able to function properly. (The acceptable range for human occupancy is considered to be 19.5 per cent to 22.5 per cent.) If the oxygen concentration drops significantly below this level, people will begin to suffer from hypoxia as the lack of oxygen starts to affect life processes. At lower levels, loss of consciousness will occur, and, with a complete lack of oxygen, brain cells will begin to die in three to five minutes. Confined spaces can become oxygen depleted by a number of processes: any form of burning, including welding or brazing; rusting (or "oxidation"), often of a steel tank; other chemical reactions involving oxidation; and biological processes involving micro-organisms can all use up some or all of the oxygen in the space.

Asphyxiant gas. Simple asphyxiants are physiologically inert gases that dilute or displace atmospheric oxygen below the level required for normal respiration. Common examples of asphyxiant gases are carbon dioxide, ethane, helium, hydrogen, methane and nitrogen. Sometimes inert gases are deliberately pumped into confined spaces: Nitrogen, for example, is often used to "purge" or force out flammable or explosive atmospheres from a confined space; it, in turn, must be replaced with fresh air before the space is safe to enter.

Toxic atmosphere. A huge variety of gases and vapours that are acutely or chronically toxic could be present in a confined space. They may consist of residues of the former contents of the space, or of gases formed by the reaction of chemicals. Gases such as hydrogen sulphide may leak into the space from gas pockets underground. Carbon monoxide may be generated in the space by the use of internal combustion engines. Methane may be generated by fermentation of plant material. The list of possibilities is a very long one. Acutely toxic gases may overcome a worker and cause him or her to become ill, lose consciousness or die. Chronically toxic gases may have immediate or long-term effects on health.

Flammable or explosive atmosphere. A fire requires fuel, heat and oxygen to burn. But a fire can become an explosion if there is one more condition: a confined space. Gunpowder just produces a flash of fire when you pour it on the ground and light it; you have to wrap it up in paper to make a firecracker. A gas or vapour that would burn out in the open will become explosive if it is confined in a tight space. So a gas or vapour can explode inside a tank and produce a great deal of damage.

The flammability of a substance depends on its "flash point" and explosive limits. Liquids can ignite when they give off enough vapour to form an ignitable mixture; this only happens above a certain temperature, known as the flash point of that particular liquid. Explosive limits are concentrations at which mixtures of flammable gas in air will burn. There is a "lower explosive limit" (or LEL) below which there is insufficient concentration of the substance to ignite, and an "upper explosive limit" (or UEL) above which there is too great a concentration for it to ignite given the amount of oxygen present in normal air. Methane has limits of 5 per cent and 15 per cent, hydrogen sulphide can be ignited in concentration between 4.3 and 46 per cent and acetylene’s range is 2.5 to 81 per cent.

Excess oxygen. In some circumstances, there can be more than 20.9 per cent oxygen in the atmosphere of a confined space. This is usually caused by leaking oxygen tanks or pipes, but it can also result from certain chemical reactions such as the breakdown of hydrogen peroxide (which turns into water and gives off oxygen in the process). Excess oxygen makes the danger of fire and explosion much greater. (The most famous example is the tragic fire in 1967 that caused NASA to stop using 100 per cent oxygen in its Apollo spacecraft. The fire, ignited by a tiny electrical spark, swept through the capsule in seconds and killed three astronauts.)

As the oxygen concentration rises in a confined space, fires (and explosions) are easier to start -- a spark from a tool, static electricity or any other source of ignition that would not start a fire in normal air can do so in an oxygen enriched environment. The range of LELs and UELs of flammable gases will become broader: Fires will be able to start at both a lower LEL and a higher UEL. Those fires will also burn and spread faster.

Material that may engulf. Another hazard of confined spaces is entrapment by material in which a worker can sink or drown. Examples include silage in a farm silo, granular material such as plastics feed stock, sand, gravel or powdered material. Often, this material has a firm surface that appears capable of supporting a worker; but it can suddenly act like quicksand, especially if it begins to flow through a chute or if it is agitated by a mixer or impeller below.

Mechanical hazards. Many confined spaces, especially hoppers and bins, contain mechanical equipment that must be locked out before any entry into the space is permissible. Hazards include things like agitators, conveyors and impellers, as well as electrical power sources.

Physical hazards. Confined spaces can contain all of the hazards that can exist anywhere; often, however, the degree of hazard is increased by the nature of the space -- the fact that it can be small and cramped, for example. Such hazards include falling objects (including ice that may build up on elevated structures), material stuck to sides and walls that may fall, slippery surfaces, noise, temperature extremes and even the discharge of static electricity.

ASSESSMENT

The first step in confined space safety is identifying all of the places that may be, or that may become, confined spaces. Some, such as tanks and pipes, will be obvious; others, like sumps or below-ground rooms, may not. A careful audit of the workplace should be undertaken to identify all current and potential confined spaces. At each location, ask "Is this a confined space? Is there any conceivable change or event that could turn it into it a confined space?"

Before a confined space can be entered, the following questions have to be asked -- and answered:

* What hazards could be present?

* What is the nature of the contaminants (acute poison, chronic poison, asphyxiant, explosive)?

* What is the concentration or potential concentration of any airborne contaminant?

* Has the confined space been isolated to prevent harmful substances from entering it?

* Has the space been ventilated sufficiently to a) maintain an adequate oxygen content and, b) to prevent the accumulation of harmful substances?

* Are there physical or mechanical hazards?

The first step is crucial. We can’t possibly sample for every known contaminant with every one of more than 200 gas detector tubes that are available. We need to examine the history of the confined space we are investigating. In order to do that, we need to ask ourselves a series of questions. What has the confined space been used for? A diesel fuel tank, for example, may be expected to contain diesel fuel, residues and vapour. What has been done to it since it was last used? Has the space been steamed, rinsed, purged, rendered inert or washed with a solvent? Add any purging or cleaning chemicals to the list and note any changes in temperature which could vaporize liquids or cause vapours to condense.

Are there other substances nearby that may have entered the space? Examine the area. Look for vents, spills and operations somewhere upwind, upstream or up a slope from the confined space. Excavations can be contaminated by hydrocarbon seepage in the soil. Liquids run downhill. Vapours that are heavier than air can flow into pits, cellars, buried tanks and sumps.

Are there any reactions that could have formed new substances? For example, fluid with hydrogen sulphide can cause iron sulphide scale to form in an uncoated steel tank. Iron sulphide is pyrophoric which means that it can spontaneously ignite in air. Rinsing with acid can remove the iron sulphide, but it releases hydrogen sulphide into the air.

This process should result in a list of substances that might be present. The next step is to gather information and consult the material safety data sheets for the substance in question.

In Alberta, it is permissible to use mechanical ventilation on a confined space and then enter it without testing. In most other jurisdictions, tests are required before each entry. Before entry is made into a confined space, a competent person, trained in the use of testing equipment, must check the atmosphere to determine the presence of harmful substances or oxygen deficiency. The reading must be recorded. Further tests should be made periodically while workers are in the space to ensure that a contaminant has not re-entered the space, or been generated, while work is in progress.

Isolating a confined space, to keep it safe during an entry, requires work on all lines leading to or from the space. There have been many "near miss" incidents because one vent line was forgotten, especially on vessels that were purged. Often, all of the production lines were properly isolated but the vent was left to bleed off the nitrogen used in purging. Later, this vent can let the nitrogen flow back in.

If the confined space contains moving parts (such as paddles, drives or augers), the main switches supplying power to the equipment must be locked out and tagged or otherwise rendered inoperative to prevent accidental activation before any entry is made. Any stored energy (be it electrical, gravitational, pneumatic or hydraulic) should be bled off after the lock is installed, and devices that can move in a dangerous manner should be secured in place with blocking or other means.

Working in confined spaces has come a long way since that days of the well-diggers’ bucket and the Davie’s Safety Lamp, but there is one factor that remains unchanged: Anyone who plans to enter a confined space must first understand the hazards, assess the situation correctly and take the appropriate measures to ensure that a confined space is no longer a dangerous place.

Dwayne Jenkins is training coordinator, and Larry Chistensen is vice-president and general manager of Standard Safety and Consulting in Edmonton, Alta.

Back to contents