Respirex International

PPE Selection for HF Alkylation

The ideal way to protect yourself from any chemical is to keep well away from it; any other mode of protection is ultimately a compromise. We need to strike a balance that allows essential work to be undertaken with  the minimum risk to health. 

Consider the following scenario; you are on-site on a sunny afternoon and everything is going well. All of the various forms of HF are present, but safely contained in tanks, pipes, cylinders etc. The site-team are meticulous in their work and there probably isn’t a drop of HF anywhere that you could actually come into contact with. But there is always a slight risk - the pipe-joint that was fine yesterday might just start to weep today. The spillage that they thought they had cleaned-up last week might actually have seeped under a tank and is now starting to come out the other side next to the walk-way. So if you are on-site it would be prudent for you to wear some sort of protective clothing. You certainly aren’t going to meet a deluge of HF, and you aren’t going out with a spanner looking for trouble. You’re just wandering around on a walk-about tour of inspection, tapping gauges, checking valves, looking at sight-glasses. You need some “precautionary” protection - jacket and trousers or a  Siren suit. You wear it in the same way that you would wear a hard-hat - you’re not expecting it to rain bricks but you put it on anyway. The jacket & trousers or Siren suit options are typically termed Class A or B protection. Workwear in our language. With these you need to consider protection for the head and neck, so you should consider a hard-hat with a fitted visor and a neck-cloth or wrap.

Now imagine that you’re on site to perform a routine service on a valve. Everything is under control, the relevant section of pipe-work has been isolated and flushed, but you know that as you undo the flange-nuts a bit of hydrofluoric acid is going to dribble out. The acid will probably fume a bit but it won’t be a problem - you’ve done the job 100 times before and you’re expecting it. Given that you are now actually expecting to encounter some HF you need to increase the level of your protection. The workwear is fine but you really need to add an air-fed hood. This will give you some respiratory protection and save your face and eyes from fumes and splashes. Or for the same job you might find a tank-suit a bit more comfortable. This level of protection is normally designated Class D. 

Lastly, we need to think of a plan for the unexpected. So far, if anything uncontrolled had unexpectedly happened your plan would have been to make a swift exit. Your Class C or D protection would have got you out of the danger-zone perfectly safely, but you wouldn’t want to hang around. So imagine that you’ve had a report of a problem - one of the forms of HF spraying out of a faulty coupling somewhere. The team who found the problem got out quickly and are OK, but now you’ve got to go in and make an emergency repair. No messing with workwear this time - this is serious. You’re not sure what you’re going to find when you get out there so you want the best protection available - a Class E gas-tight suit. 

It is vital that wearers have full confidence in their protective clothing and as such employers have a moral responsibility to ensure that the PPE they provide gives adequate protection.

Material Selection

The choice of material will determine both the likely life-span of the garment, its operator comfort and the degree of chemical protection it can provide. For HF refinery applications Respirex recommend neoprene for Class A to D applications, as it offers greater chemical protection than PVC and is more flexible, making it more comfortable for the user. It is important to remember that these garments are the routine uniform for the site - they have got to be more than just “wearable”.  

For workwear and air-supplied suits neoprene has sufficient permeation resistance to anhydrous HF to get you out of danger. For Classes A to D there is no benefit in choosing fabrics like Viton/Butyl/Viton; the level of protection offered by the garment design doesn’t warrant such high permeation resistance. If the environment is sufficiently hazardous that you need hours of protection against HF gas you will certainly need gas-tight seams, gas-tight foot-wear options and gas-tight seals everywhere. 

However, for the gas-tight suit scenario, where you have accepted that the environment warrants the use of a gas tight suit, you do need the superior permeation resistance of either VBV or DuPont™ seven layer barrier material. The good news is that the design of this suit does warrant this extra resistance. 

Share this: