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Next by Date: Subject: [DCHAS-L] Chemical Safety headlines (9 articles) Date: Mon, 8 Aug 2022 06:31:56 -0400 Author: Ralph Stuart |
The lack of awareness and appreciation of the potential explosion hazards of even small amounts of light hydrocarbon solvents, under "not-so-lucky" conditions, is pervasive in society as well as the hydrocarbon process industry.
I always thought that expressing the hydrocarbon (vapor) mass in terms of an "equivalent" TNT-mass helps.
For example, the heat of combustion of 2methylbutane is 46,000 kJ/kg, a number that is pretty well standard for all simple aliphatic hydrocarbons, while the explosion energy of TNT is 4,602 kJ/kg ("Understanding explosions", a CCPS concept book by Daniel A. Crow). Only the TNT's explosion energy (released during the detonation stage) is used for comparison purposes, a secondary after-burn energy release (during the slower air oxidation of detonation products stage) is not included. This makes it makes it a comparing of "apples and oranges" process; however, it provides a simple basic multiplication factor of 10 and brings a more tangible hazard message along.
Running some numbers for 2methylbutane in a household fridge:
2Methylbutane (isopentane) has a stoichiometric concentration in air of 2.55 vol-% (from "Avoiding Static Ignition Hazards in Chemical Operations", a CCPS concept book by Laurence G. Britton). The LFL and UFL (**At_Symbol_Here** 25 C) are 1.4 and 7.6 vol-%, respectively.
To achieve a homogeneous stoichiometric gas cloud in equilibrium with liquid 2methypentane, the temperature would need to be at approximately -48 C (NIST-Data on 2methylbutane saturation curve).
This seems unrealistic for a household type refrigerator and the explosion of the fridge was therefore not as bad as it could have been.
Assuming that the fridge, under consideration, had an available air space of 1 m^3 and a slowly increasing airborne 2methylbutane concentration, because of vaporizing 2methybutane. This (homogeneous) airborne 2methylbutane concentration continue to increase until the LFL concentration had been reached, at which point ignition occurred.
At that time there was 0.014 m^3 2methylbutane or 0.041 kg in the air space. The liquid volume of this mass (25 C) equals 6.6125e-5 m^3 or 66 ml (NIST: Liquid volume of 2methylbutane: 0.0016261 m3/kg).
The homogeneous atmosphere is a conservative assumption and the 1 m^3 open space is probably a bit conservative, the 50 ml (liquid) 2methylbutane looks like a reasonable number.
Jan Windhorst
WEC Inc
-----Original Message----- > >Explosion proof has two meanings when applied to a hood. 1. I had a call from a lab tech who was concerned because they had an explosion in a standard fume hood and the projectiles had cracked the sash. Replacing the sash would going to cost most than $1000. They wanted an assurance that the replacement wouldn‰??t crack if the same explosion happened again. My response was ‰??How big an explosion are you planning on having in the fume hood?‰??. There was no response when they realized that an explosion was not part of their work plan‰?| 2. We had an explosion in a household style refrigerator on another campus. This laboratory had left isopentane in the refrigerator over night to cool down for use the next day. The isopentane leaked into the cooling compartment and when the thermostat flipped on, the resulting spark triggered the explosion. We learned in discussions with the lab tech, the amount of isopentane likely to have leaked was less than 50 ml. But the amount of energy when the solvent ignited in a sealed container was enough to destroy the refrigerator, scatter lab debris across the lab, and pop out all the ceiling tiles in the room. Fortunately, there was no one in the room when the explosion occurred. The point is that there is a lot more energy in small amounts of solvents than people using these chemicals as reagents recognize. - Ralph Ralph Stuart, CIH, CCHO --- ---
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From: ACS Division of Chemical Health and Safety
Sent: August 4, 2022 6:18 AM
To: DCHAS-L**At_Symbol_Here**Princeton.EDU
Subject: Re: [DCHAS-L] iron pentacarbonyl
>
I have had two specific experiences that were impacted by this confusion:
ralph**At_Symbol_Here**rstuartcih.org
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