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Spray cans storage

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Written by Administrator
Saturday, 01 August 2009 10:50

August 2009

Spray cans are a very common item, either at home or in the plant, on production lines, for maintenance purposes, for non destructive testing applications, for corrosion inhibitors spraying, etc.

Another paper deals with the propellents, which may be either compressed gases (Nitrogen, Carbon Dioxide, sometimes Nitrogen Protoxide) or liquefied gases (light hydrocarbons such as butane and propane, dimethylether).

Compressed gases are non flammable, but the "active product" (the product propelled out of the can for use) may be Flammable, or Highly flammable. The non flammable gas then has almost no influence on the flammability of the product expelled from the can, as compressed gases are generally non soluble in active products.

Liquefied gases are classified as "Extremely flammable", and generally the spray cans using these gases are also classified as extremely flammable.

Therefore a lot of spray cans are more or less flammable ... and storage problems come from an insufficient understanding of the cause for danger by users!

The main danger by far due to spray cans is the increase of the pressure if heated...during a fire for instance. As the spray can can resist only to a certain pressure, as compressed or liquefied gases pressure quickly increases with temperature, there is a limit of temperature that the can is able to withstand. European regulation requires the limit be stated at 50°C (122°F) on the label. In fact the spray cans sold on the European market may face temperature up to 70°C (158°F) without breaking risk.

Can's rupture frees large quantities of flammable products which, if released during a fire, or near a flame, will burn very easily and worsen the situation.

Quite often industrial users store several hundreds of spray cans, for different applications. They are worried by the "Flammable" or "Extremely Flammable" label.

The worst thing to do is to store huge quantities of flammable products in a closed, airtight area.

As a container under pressure, a spray can is "allowed" to release up to 11 grams (0.39 oz) every year. Not so much for one spray can. But when we saw 700 spray cans stored in a massive, airtight locker (very similar to a ... safe!) in an office ... we were amazed!

This "safe" was closed the most part of the week, opened only for replenishing or taking out the needed cans.

We explained people in the office that this was especially dangerous! All the spray cans were butane/propane propelled, all the active products were flammable or highly flammable.

Flammable vapours may store up, up to the lower flammable limit (LFL) ... and any flame, or incandescent point (cigarette ashes: smoking was then allowed in offices), or a spark could have catastrophic effects!

We explained that in any storage of chemicals, with very few exceptions, the best way is to have a ventilated area to allow for vapours exhaust. This system may be without any fan. What is needed is:

• One way in for fresh air, preferably near the top of the locker.

• A similar way out surface on the opposite side, at the bottom of the locker, preferably connected to the outside.

• To keep in mind that, apart from very very few exceptions, vapours from chemicals are ALWAYS heavier than air: better to have exhausts AT THE BOTTOM of installations. Doing so exhausts systems have an easier job, and when workers are in the area, vapours do not go up to their noses and lungs as they do if exhausts are above the workers!

Let's come back to the 700 spray cans. Guess a 4 x 2 x 0.5 meter (4.1 x 2.05 x 0.5 yard) cabinet. Inside volume would be: 4 cubic meters (5.23 cubic yards) ... but 700 spray cans come to almost 3 cubic meters (3.92 cubic yards). Hence an air volume of ca 1 cubic meter (1.31 cubic yards). Knowing that the lower flammable limit (LFL) of the chemicals is in the 1.2% range, that means 12 litres of gas would be enough. Assume an expansion ratio of 250 when a liquefied gas evaporates (that's an average figure). That comes to 48 ml to leak from spray cans. With a density of 600 kg/m3 (liquid butane) that comes to less than 30 grams of butane. Further due to its relative density gaseous butane would be prone to stay at the bottom of the locker ... where ashes could fall down ...!!!

You may imagine that, though the airtight locker was expensive, people in the company were quick to find funding for an appropriate locker!

Last Updated ( Sunday, 22 May 2011 19:19 )