The Risk Management Tool Box Blog

What is the Lower Explosive Limit?

Graham Marshall - Monday, September 24, 2012

Chemical storage vessels and drums that have contained flammable liquids, such as fuels, solvents, and paints can ignite or explode when exposed to “hot work” such as sparks from angle grinders, plasma cutters, welding, oxyacetylene burners and electric metal cutting saws.

This is because flammable liquids give off vapour which has an upper and lower explosive limit that works like a range.  That means that vapour can ignite and/or explode when it is below the upper explosive limit (UEL), but above the lower explosive limit (LEL).  When a flammable or combustible liquid is exposed to heat (from direct or indirect flame), the vapours given off can reach into the range between the LEL and the UEL and ignite.  This reaction can cause a fire or an explosion. Such explosions have resulted in many fatalities occurring or severe burns from the resulting fire.

As recently as July 2012, a West Australian worker was killed when a chemical drum that he was cutting with an angle grinder exploded. The drum had previously contained a flammable liquid.

In another recent case, a Queensland high school student was killed when he was using a plasma-arc torch to convert a drum into a feed bin as part of his agricultural studies. The drum had previously contained diesel oil and the oil vapours that remained in the drum exploded.

The first step towards managing the risks associated with the UEL and LEL of any potentially explosive chemicals is to obtain important safety information.

The manufacturer or supplier of the chemicals must provide this information with the chemicals they provide. The information should be provided by a Material Safety Data Sheet (MSDS) that contains information about the hazards associated with the chemical and precautions for the safe use, transport, storage and disposal.

The MSDS should include information such as the temperature that will allow vapours to rise above the LEL and subsequently ignite, and the levels of exposure that are hazardous to humans through The chemicals should also be labeled in a way that can be easily read and understood.

If a drum of chemicals arrives at the workplace without a safety label and an MSDS attached, it should be returned to the supplier.

Once emptied, the storage containers should be stored in a safe location, away from ignition sources, with their labels still attached.

The best way to prevent an injury or fatality is to ban any form of hot work on or near a vessel or drum that contained (or still contains) flammable or toxic materials.

If hot work must be undertaken, then a Permit to Work should be issued following a thorough assessment of the task to be undertaken, and ensuring all appropriate controls are in place.

It is essential that competent, experienced persons who are familiar with the hazards associated with hot works review all hot work prior to issuing approval for the work to proceed.

It is also critical that workers performing any hot-work are provided with adequate training about the hazards associated with conducting hot work on or near drums that contained flammable or toxic substances.

Mexican Gas Pipeline Fire

Graham Marshall - Wednesday, September 19, 2012

A big fire erupted at a natural gas pipeline distribution center yesterday, near Mexico's border with the USA, killing at least 26 maintenance workers and 46 other workers were injured, including two hospitalized in serious condition..

The pipeline carries natural gas from wells in the Burgos basin.

The fire forced the evacuations of people in nearby ranches and homes with civil protection officials clearing the area within three miles of the gas facility.

The highway that connects Reynosa to the industrial city of Monterrey was also closed to traffic during the emergency.

The death toll included a man who was run over when he rushed onto a highway running away from the facility.

The fire was extinguished in 90 minutes and the pipeline was shut off.

There is no evidence showing it was a criminal,  sabotage or terrorist attack.

It appears that there was a gas leak, followed by an explosion, but the precise cause had not been determined.

Pipelines carrying gasoline and diesel in Mexico are frequently tapped by thieves looking to steal fuel.

Several oil spills and explosions have been blamed on illegal taps. But thieves seldom target gas pipelines.

In December 2010, authorities blamed oil thieves for an oil pipeline explosion in a central Mexico City near the capital that killed 28 people, including 13 children.

That fire burned people and scorched homes, affecting 5,000 residents in an area six miles wide in San Martin Texmelucan.

Switchloading Safety Alert

Graham Marshall - Thursday, August 30, 2012

If a flammable or combustible liquid is to be filled into a tank or vessel that previously contained a liquid with a lower flash point, the process is called "switch-loading", and it can be particularly hazardous if appropriate controls are not in place.

Switch-loading often occurs when a combustible liquid such as diesel is pumped into a tank that has previously contained petrol and static electricity is the main triggering risk-factor.

Whilst the tank may have been emptied of liquid petroleum, it is still likely to still contain flammable petrol vapours that could ignite.

In Australia, the relevant Standard for control of switch-loading is AS1940:200 ("The storage and handling of flammable and combustible liquids").

Under such circumstances, AS1940:2004 recommends a number of risk control measures to be in place.

The following are some of the control measures that should be considered to reduce the risks from static electricity:

•  All tanks, pipework, transfer systems (including decanting) and process plant associated with dangerous goods should be electrically bonded to each other and earthed, or otherwise protected (see AS/NZS1020 and AS4979 for advice):
•  Completely drain previously loaded liquid with the lower flashpoint;
• ‘Gas free’ the compartment where appropriate;
•  Reduce loading rates to less than one m/s until the fill pipe is submerged;
•  Use anti-static additives in non-conductive liquids; and
•  Ensure that the hose and hose assemblies are appropriate for use with petroleum products.

Enclosed here is a Safety Alert with further information on switch-loading.

Flammable Vapour Cloud Risks

Graham Marshall - Monday, August 13, 2012

In December 2005, a flammable vapour cloud was released at the Buncefield fuel depot in the UK, ignited and caused several explosions after a large petrol-storage tank was overfilled. 

Numerous investigations were conducted into the causes of the incident, with the latest UK HSE report looking into how different tank designs are likely to behave if they overflow causing a vapour cloud. 

The work provides a first step towards developing a mathematical model which will predict the likely size of flammable vapour clouds based on simple measures such as the tank dimensions, tank design type, pumping rates and liquid composition.

Three main types of storage tank are identified in the report which are each likely to produce different flow behaviour in the event of overfilling:

+    Fixed roof tanks with vents;

+    Fixed roof tanks with pressure/vacuum valves; and

+    Floating deck tanks with no fixed roof.

The likely release scenarios from overfilling each of the tank designs are discussed.

The UK HSE report into flammable vapour cloud risks can be found here.


Safety Checklist for Petrol Station Operators

Graham Marshall - Monday, July 30, 2012

Petrol filling stations are potentially dangerous places because the general public with little or no training actively handles a range of classified dangerous goods.  These hazardous substances included flammable liquids like petrol, liquefied petroleum gas and combustible liquids like diesel.

But refilling a vehicle on a garage forecourt is so routine that it may be thought to be an entirely safe process.

And although it is true that very few incidents occur at petrol stations, the accidents that do occur can have very serious consequences.

Many people are injured and some are killed each year resulting from incidents when refueling vehicles.

The risk potential can, however, be minimized by implementing simple controls that prevent incidents or assist in responding to them should they occur.

To start with, petrol station operators must ensure that their employees are not complacent about the hazards at work.

Employees must be well trained in emergency response procedures so they can react immediately and appropriately to incidents.

To assist operators ensure that good controls are in place, this free self-check guide will assist in the safe operation of supervised self-service petrol stations.

The free checklist identifies key elements that an individual without extensive knowledge or training can check.

Attending to these key elements can significantly minimize the risk from dangerous goods at petrol stations.

Use of Angle Grinders on Propane Tanks

Graham Marshall - Friday, July 06, 2012

A worthy nomination for a Darwin Award here when a workman in the UK was seriously injured whilst removing the top of a full propane gas tank with an angle-grinder!  We're not sure why anyone would actually want to do this?

In a prosecution by the UK Health and Safety Executive (UK HSE), Southampton magistrates heard that the 29-year-old worker suffered serious burns to his arm and body after propane caught fire.  Now there is a surprise!

The employee was lucky not to have been killed.  Yes, indeed.

Jamie Jewell, a Company Director of a company known as Suffix Pre-Cast, who was "supervising" the workman admitted breaching the UKs Health and Safety at Work Act.  He was fined £2,000 and ordered to pay costs of £2,451.

The UK HSE prosecution alleged that Jewell did not know enough about the hazards of handling propane gas to carry out the work competently or supervise others.

The incident, which involved a full tank of propane gas, occurred at Jewell’s Calmore home on September 2nd  2011.

Would you walk into a pool of gasolene?

Graham Marshall - Friday, June 29, 2012

How would you react if you observed a large pool of petrol escaping from a Petrol Tanker Truck?

The footage below shows an example of several people putting themselves in harms way by walking into a pool of gasolene pouring from a tanker.  A cyclist even rides through the middle of the spill.

The video was used by the UK Health and Safety Executive (UK HSE) in a recent successful prosecution of a fuel terminal operator.

The footage shows - in stark form - how people can react when called upon to manage a known serious hazard event.  In this case - amazingly badly!

To view the footage, simple click here.  You'll be amazed!

Cal OSHA investigates Oil Tank Fatality

Graham Marshall - Wednesday, June 27, 2012

The dangers associated with performing hot work on oil storage tanks have been re-highlighted by a fatal accident in California.

Cal OSHA is investigating the explosion which occurred when two workers were decommissioning a crude oil tank.

The explosion killed one man, critically injured another and leaves questions unanswered about what safety procedures the men used as they worked on the tank.

The men were using a cutting torch on top of the tank when vapors inside ignited, blowing the 16,800-gallon container some 30 feet in the air and a distance of 79 feet.

The Kern County Fire fire department reported that Cesar Martinez, 24, was blown 40 feet into the air and more than 900 feet distant.

The other worker, identified by their employer Sky-Brand Services as 33-year-old Eric Robles, was also injured.

Both workers believed the tank was empty.

Cal-OSHA investigators determined the two men were assigned to demolish the tank and that Martinez was removing pipe that was to be recycled as scrap metal.

Agency spokesman Peter Melton said “he was using a cutting torch on an enclosed pipe, and apparently gas might have escaped and it ignited". It was unclear who owned the tank and when it was decommissioned, he added.

Sky-Brand partner Dale Hill said Martinez and Robles were removing steel pipeline from the exterior of the tank.

He said the company has done similar work on numerous oil tanks and hasn’t had problems.

“We do everything we can to make sure every precaution is being taken,” Hill said.

In the oil industry, however, the common practice is to keep all flames at least 50 feet away from an oil tank, unless it has been thoroughly cleaned and purged, vented, tested for residual gas and isolated from other "live" processes.

“Fire and gas, they don’t make a good combination,” he said.

Sky-Brand specializes in site cleanup and demolition work, removing scrap metal and selling it, Hill said.

Cal-OSHA’s Melton said the agency’s investigation could take up to six months, during which time it hopes to find out exactly what the two men were doing, what safety precautions were taken, what regulations apply to demolishing such equipment and whether the right tools were being used.

Fire extinguisher audit

Graham Marshall - Sunday, June 10, 2012

When it comes to HSE management activities, I use the analogy that the "one per-centers" are the simple every-day actions and behaviours that we must always get right.

If an organization can't get the "one per-center's" right, how on Earth is it going to deal with the more complex stuff? 

Here is another "one per-center" to look at in your workplace today:

  • Check all the fire-extinguishers in your location;
  • Are they all present (none removed or stolen)?
  • Are they all adequately charged?
  • Have they been recently checked and certified? 


Remember, if you can't do a simple thing like fire-extinguisher audit, how are you going to succeed with the harder HSE problems in the rest of 2012?

Seafarer Safety Alerts

Graham Marshall - Wednesday, May 30, 2012

Just a short post today to highlight two recent safety alerts.

The first one, deals with lessons learnt from a toaster fire.  Click here.

The second one deals with issues surrounding long-term storage of fire extinguishers.  Click here.


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