Daniel Marshall Archives - International Mining

Due to their size, speed and high-horsepower drive motors, conveyors pose a number of risks to personnel working on or near them. In addition to all the physical danger zones, when an injury occurs, ‘fault’ is often attributed to injured workers’ actions or inactions. However, safety experts point out that injuries generally occur due to a series of factors.

“Accidents are typically a result of a complex combination of probabilities, rather than a single unsafe act,” Martin Engineering Process Engineer, Daniel Marshall, observed. “Except for the unsafe act, it can be said that the accident would not have occurred if there was a safer design, better maintenance or less pressure for production.”

Assessing the risk of a conveyor

A thorough risk assessment by trained professionals is the ideal way to bridge the gap between workers and managers when the rules need review, to identify hazards and implement controls to reduce risks.

“A belt conveyor is a powerful machine with thousands of moving parts,” Marshall continued. “These moving components might severely injure a worker and can produce that injury in a fraction of a second.”

A typical conveyor belt moves at a relatively constant speed, commonly running between 0.5-10 m/s. At the very minimum, a worker who inadvertently touches a running conveyor belt – even with world-class reaction time and total focus on the danger of a conveyor – will come in contact with at least one carrying idler, and the potential is there to hit return idlers, chute uprights, stringer supports, pulleys and drives. The results are often disastrous.

Working around a moving conveyor

It has been estimated that two thirds of the fatalities involving conveyor belts take place while the belt is moving, usually because of a worker becoming entangled or crushed by moving equipment. Most of these take place when maintenance or housekeeping is being done on or around an energised conveyor.

*Conveyor service should be performed only when the belt is properly locked, tagged, blocked and tested*

These fatalities are generally caused by two compounding practices. The first is performing maintenance without thoroughly locking, tagging, blocking and testing the conveyor. Another unsafe practice is touching a moving conveyor belt with a tool or implement of any kind. When these two choices are combined, the results are usually severe and often fatal. Even working on a conveyor that is turned off, but not locked out, can lead to tragedy.

Workaround and shortcuts

“An intelligent and creative worker will often invent or discover ways to expedite certain functions or make work easier,” Marshall said. “Unfortunately, some of these shortcuts bypass safety hardware and/or best practices, putting the worker in harm’s way.”

The most common of these workarounds involves the “improper locking out” of a conveyor system, Martin Engineering says. The purpose of a lockout is to de-energise all sources of energy, whether latent or active. Failure to properly lockout can exist in many forms – varying from disregarding lockout requirements, to working on a moving conveyor, to improperly stopping the conveyor. An example would be pulling the emergency stop cord and assuming that the conveyor is de-energised.

Another common workaround involves entering a “confined space” without following established procedures. A confined space is any enclosure that is large enough and configured so that an employee can enter and perform assigned work, has limited or restricted means for entry or exit and is not designed for continuous employee occupancy. Very specific rules apply to workers when dealing with confined spaces. Failure to follow those rules can result in increased danger or death, Martin Engineering says.

Other potential unsafe behaviors include crossing a conveyor in a risky manner. Conveyor belts are often lengthy systems bisecting a production facility. Workers may be required to cross a conveyor line to get to an area in need of service or maintenance. To save time, a worker is likely to step over or cross under a conveyor.

“Crossing under” offers multiple hazards, according to the company. If any of the worker’s body parts come in contact with the moving conveyor, it will either act like a grinder and abrade the skin or pull the worker toward rolling components. Crossing under also places the worker at risk from falling objects.

*Taking a shortcut by crossing over or under a conveyor can lead to injury*

“Crossing over” a conveyor without using a designed and designated crossover structure comes with dangers, as well. There is a high potential for a slip and fall. If lucky, the worker may fall on the ground; if not, the worker will fall onto the conveyor belt. If the conveyor is in operation, the worker may be carried downstream. This can result in contact with the conveyor structure and rolling components or being thrown off the conveyor at the discharge. The safe approach to crossing a conveyor is to use a designated crossover or cross-under point engineered for that purpose, Martin Engineering says.

Anything in a worker’s line of travel is a potential “obstruction”. These can range from piles of spillage, items lying on the walkway or work areas, as well as low overheads. An obstruction can cause several hazards, the most obvious being the opportunity for a trip or fall. If the obstruction is in the middle of the walkway, a worker will have to go around it. If that revised path brings the worker closer to a conveyor, this decision places the worker closer to the hazards of the conveyor.

Neglected safety and control mechanisms

“Emergency stop pull cords are the last line of defence if the belt needs to be stopped quickly in response to an entrapment or impending equipment failure,” Marshall said. “The reaction time when such an event occurs is usually extremely brief, so workers need a way to stop the conveyor as fast as possible. In addition, the belt will not halt immediately and must coast to a stop. If the cord is broken, the switch is not working or the system is disabled, workers have lost the one final tool they have to protect themselves.”

The multiplying effect of unsafe practices

Often an accident occurs due to a combination of several poor work practices. A Mine Safety and Health Administration (MSHA) Fatalgram from 1999 in the USA recounts an event that caused a fatality at a mine when a worker entered an unguarded area alone, near an operating conveyor that was not locked out. The worker’s clothing then became trapped in the conveyor’s operating tail pulley. Four unsafe practices and two unsafe areas combined to produce a catastrophic event. Any individual factor may have led to injury or even death, but the combination essentially sealed the worker’s fate.

In a 2003 study, ConocoPhillips Marine found a correlation between fatalities and unsafe practices. The study showed that for every fatality there are an estimated 300,000 unsafe behaviors.

The research also quantified lost-time accidents, recordable injuries, and near misses. These are independent variables, so the numbers do not mean that lost day incident number 31 will be a fatality. But they do indicate that there is a statistical probability of a fatality for every 30 lost workday incidents. As a result, statistically speaking, an effective way to reduce fatalities is to reduce unsafe behaviors.

*The most effective way to reduce fatalities is to minimise unsafe behaviors*

“While even one unsafe practice has the statistical potential to lead to serious repercussions, conveyor accidents are rarely the result of a single action,” Marshall concluded. “More often, they result from a combination of company culture and unwise decisions. If workers can eliminate these unsafe practices and minimise their presence in danger zones, their chances of avoiding an accident will improve considerably.”

Martin Engineering, a global innovator in the bulk material handling industry, is urging operators to locate safe access points before attempting to unblock chutes, silos and hoppers in order to prevent potential accidents on site.

As the company says, many factors can cause bulk materials to adhere to the sides of chutes, silos and hoppers – including humidity, moisture content, size/texture of the raw material or increased production volume – resulting in lost capacity or clogging.

Ongoing accumulation reduces flow and eventually stops production in order to address the issue, causing expensive downtime and requiring extra labour to clear the obstruction.

Martin Engineering Product Engineer, Daniel Marshall, said: “Clearing extensive build up often involves confined space entry, but the consequences of untrained staff entering a chute, silo or hopper can be disastrous, including physical injury, burial and asphyxiation.

“Without proper testing, ventilation and safety measures, entering vessels containing combustible dust could even result in a deadly explosion.”

What is confined space entry?

The US Occupational Safety and Health Administration (OSHA) defines “confined space” as an area not designed for continuous employee occupancy and large enough for an employee to enter and perform assigned work, but with limited or restricted means for entry or exit. “Permit-required confined space” means a confined space that has one or more of the following characteristics:

The vessel contains or has the potential of containing a hazardous atmosphere such as exposure to explosive dust, flammable gas, vapour, or mist in excess of 10% of its lower flammable limit;
Atmospheric oxygen concentration below 19.5%, or above 23.5%;
There is the potential for material to engulf, entrap or asphyxiate an entrant by inwardly converging walls or by a door which slopes downward and tapers to a smaller cross-section; or
Contains any other recognised serious safety or health hazards.

Entering a confined space

Working in confined spaces typically requires special personnel training, safety harness and rigging, extensive preparation and added personnel for a ‘buddy system’.

Marshall continued: “Systems designed to minimise permit-required confined spaces can provide a significant return on investment and the best time to reduce the amount of confined-space entry for component maintenance and replacement is during the specification and design stages of a project.”

Many manufacturers offer systems and products that can reduce the need for confined space entry.

Examples would include:

Modular chute designs with abrasion-resistant liners;
Chutes that hinge open and lay down for liner replacement;
Skirtboards with external liners;
Belt cleaners that can be serviced without confined space entry;
Flow aids such as air cannons and vibrators to reduce build up; and
Modular air cleaners for specific locations rather than centralised dust collection.

Global regulations, standards and best practices

Rules regarding confined space entry vary greatly depending on the country, even down to the state, province or prefecture level. As always, regional and local codes should be identified and followed, but general rules can be drawn from regulations established in major industrial markets such as Australia/New Zealand, Canada and the United States. Commonalities between governmental regulations provide employers with a measured approach to safety.

Prior to starting the job, these procedures include:

Review the permit and the job-specific work procedures;
Gather and inspect all necessary PPE;
Test and/or calibrate any safety gear, test instrumentation or communication tools;
If a current Job Safety Analysis or safety check list does not exist, perform a risk assessment;
Hold a pre-job meeting making sure all workers are aware of the hazards and safe work practices;
Conduct proper tests for toxins, vapour, dust levels, oxygen levels and material-specific hazards;
Perform as much cleaning and maintenance as possible outside of the vessel;
Post completed confined space entry permit outside of the vessel;
Isolate contaminants and moving parts to prevent the accidental introduction of materials; and
Proper lock-out/tag-out/block-out/test-out procedures must be completed and documented prior to entry.

During the procedure, they include:

Perform maintenance/cleaning using non-toxic substances such as water and avoid using heat/fire in the confined space. Never use oxygen to purge a confined space, as this can create a fire and explosion hazard;
Provide ventilation if possible;
Select personal protective/safety equipment such as safety helmet, gloves, hearing protectors, safety harness and lifeline and breathing apparatus;
Assign a trained observer to monitor the procedure and internal conditions, and provide escape assistance if needed; and
Practice fast evacuation of the confined space.

“Over time, well-designed access improves safety and saves money,” Marshall said. “Safe access that is carefully located and adequately sized will increase dependability and also reduce the downtime and associated labour required for maintenance.”

He advises that companies consider equipment designs which minimise the need for confined space entry, including improved access doors, vibrators, air cannons or silo cleaning services.

“Conveyor systems that are properly outfitted with appropriate cleaning and material discharge equipment create a safer workplace, while experiencing longer life and less downtime,” he concluded.

Addressing unsafe work practices around mining conveyors