SWS Environmental Services Presents:
Hydrogen Fluoride Emergency Response
It’s a slow day at the station when a call comes in for a hazardous materials spill at a commercial car wash.
Dispatch advises the caller reported the spilled hazmat is corrosive, but they did not give a chemical name.
▪ ERG advises guide 153 – Substances Toxic and/or Corrosive based on a corrosive material reported by the caller.
o Guide 153 lists the Primary Hazard as a Health Hazard.
o As an immediate precautionary measure, an isolation distance of 150 feet is recommended.
▪ What could this “hazmat” be?
Upon arrival at the car wash, the caller meets you and gives you the Safety Data Sheet. The product is wheel cleaner used in the automated wash line. While a worker was changing out an empty 55-gallon drum of the wheel cleaner with a full drum, the full drum fell over. The wheel cleaner began spilling out of the 2 1/2” bung and splashed onto the worker.
When you review the SDS, you find that the wheel cleaner contains Hydrofluoric Acid at a concentration of 4.5% and could contain up to 5% Sulfuric Acid. The First Aid Measures advise flushing for 5 minutes with water and then treating with a solution of 0.13% iced Benzalkonium Chloride or 2.5% Calcium Gluconate Gel.
▪ What is this Hydrofluoric Acid?
Hydrofluoric Acid or HF is found in a variety of industrial and residential products such as chrome wheel cleaners, glass etchants, and for stainless-steel pickling. HF is used in various industrial applications to produce gasoline, refrigerants, soaps, and incandescent light bulbs.
HF can be transported as Anhydrous Hydrogen Fluoride (AHF) or Hydrofluoric Acid, with 90% of all AHF transported by rail. HF on the other hand can be found in mixed loads in addition to bulk tank trucks and Intermediate Bulk Containers. So, it is imperative to always check the consist or bill of lading to determine the contents of the shipping container.
HF is hazardous to humans through inhalation, ingestion, and direct contact. Without the correct medical attention, even low concentrations can be hazardous to human health with delayed effects. Any HF exposure requires immediate specialized medical treatment. If proper medical treatment will be delayed, then response actions must be re-evaluated to determine if entry into the area is warranted. It cannot be stressed enough that immediate medical treatment is critical! When responding to reported corrosive hazardous materials spills, determining early on what is the exact composition of the product is important. Although low concentrations are handled relatively safely, concentrations greater than 50% in solution can be fatal by inhalation due to the amount of vapors being released. If a visible vapor can be seen releasing from a container containing HF, it can be safely assumed the concentration is over 50%. However, solutions as low as 40% can fume if the product is spilled on a hot surface such as a hot macadam highway in Texas in August and solutions of 45% to 50% can fume if the air temperature and humidity levels are above 85°F and 70% respectively.
• What to wear, what to wear?
So, you may be wondering, what do we do about skin protection? Depending on the capabilities of your department or district, it may be necessary to call out the Hazmat Rig or a local Hazmat Response Team such as SWS Environmental Services. Skin protection is critical at any concentration of HF. Even properly trained and equipped response teams must take the time to determine the proper chemical protective clothing based on the concentration of the HF in the spilled product. Chemical protective clothing that is good for Hydrofluoric Acid may not be suitable for anhydrous or 100% HF. Do not rely solely on the SDS for chemical protective clothing recommendations; use a minimum of 3 sources of information. Besides the SDS, you could use the chemical protective clothing manufacturer’s permeation data to select the proper chemical protective clothing. Prior to consulting these information sources make sure you verify the strength and physical state of the material.
• What about the air?
Ok, so now that we have our chemical protective clothing, what about respiratory protection? Again this is going to come down to the concentration of the HF in the spilled product. For an airborne concentration up to 30 ppm, which is the amount that is Immediately Dangerous to Life and/or Health (IDLH), responders can wear an Air Purifying Respirator (APR), Supplied Air Breathing Apparatus (SABA or Long-Line), or a Self Contained Breathing Apparatus (SCBA). An air purifying respirator must have cartridges that provide protection against HF. But you must consider the maximum use concentration (MUC) for the type of respirator in use prior to making entry. Since an emergency scene is not the best location to be researching the best respirator to be used, this should be done prior to an emergency response.
• Breathe easy
Let’s take a closer look at the MUC when selecting an APR for an HF response. If we have a Full-Face Air Purifying Respirator, it will protect the user up to 50 times the Permissible Exposure Level (PEL); the PEL for Hydrogen Fluoride is 3 ppm. By doing the math (50 X 3 = 150), this APR “could” protect the user up to 150 ppm of HF vapors in the atmosphere, correct? As good as that sounds, an APR can only be worn up to 30 ppm or the IDLH for HF. Now that we have done some pre-planning, we have a better idea of what respiratory protection will be needed. But do not forget that even low concentrations of HF vapors can be hazardous to a responder’s respiratory system.
• Level the playing field
Now that we have determined our chemical protective clothing and respiratory protection needs, we have to decide what our level of protection should be; Level A or Level B. This will be determined by what the entry teams will be doing in the Hot Zone. If they are simply making an entry for reconnaissance and air monitoring then Level B would be acceptable, but if they are attempting to plug a leaking container, then Level A would be the choice. Remember that this decision must be based on the concentration of the HF in the spilled product and the atmospheric concentrations.
What about measuring the atmospheric concentrations to determine the correct level of protection? Well, there are many choices available for atmospheric monitoring, but not all of them are useful for HF. What about the Flame-Ionization Detector (FID)? Well, HF is not flammable, so that will not work. Ok, what about a Photo-Ionization Detector (PID)? One must consider that, even if our PID had the strongest available lamp, an 11.7eV, it is not strong enough to detect HF which has an Ionization Potential of 15.98eV, so the PID will not work. What about multi-sensor detectors? Some of these can be configured to detect HF but they are very expensive, must be specifically configured, and have cross-interferences that could give false-positive responses. So what does that leave us? Colorimetric Detector Tubes! The detector tubes are a recognized and generally accepted good engineering practice that are simple to use, generally chemical specific, require no calibration, and fairly inexpensive. Just remember to follow the manufacturer’s instructions, ensure the tubes are not expired, and only use tubes in the pumps for which they were designed.
• HF comes in a many shapes and sizes.
So how is HF transported and stored? In transportation, it can be found in a variety of containers including 1-gallon bottles, 55-gallon drums, 300-gallon intermediate bulk containers, up to 5,000-gallons (35,000 lb.) in truck-trailers, up to 6500-gallons (52,000 lb.) in ISO containers, or up to 25,000-gallons (172,000 lb.) in rail tank-cars. HF can be transported as Anhydrous or Aqueous. Anhydrous HF is any concentration over 99.9%; all other concentrations are considered Aqueous. But as we have already mentioned, even low concentrations are highly hazardous to humans. At industrial locations, HF will be found in above-ground storage tanks or ISO containers. A manufacturer may have HF in drums at concentrations below 50% and then dilute the HF for use in their particular process. This is commonly found in metal plating lines and the semi-conductor industry.
• What about the pH?
What’s next? What about neutralization? HF is an acid so just grab any mild base and start neutralizing right? Hold on, HF is not any normal acid, and we cannot just start throwing neutralizers on it before looking at some considerations.
Hydroxide neutralizers [NaOH, KOH, CaO, Ca(OH)2] have a high heat of neutralization but have a neutral product solubility.
Carbonate neutralizers [Na2CO3, CaCO3, NaHCO3] have a very low heat of neutralization but have a rapid evolution of carbon dioxide gas.
• Sodium Hydroxide NaOH: Corrosive and causes an extremely high reaction temperature. Produces Sodium Fluoride
• Potassium Hydroxide KOH: Corrosive and causes an extremely high reaction temperature. Produces Potassium Fluoride
• Sodium Carbonate Na2CO3: Easy and safe to store/handle and low reaction temperature. Produces Sodium Fluoride and Carbon Dioxide
• Sodium Bicarbonate NaHCO3: Easy and safe to store/handle and low reaction temperature. Produces Sodium Fluoride and Carbon Dioxide
• Calcium Carbonate CaCO3: Low reaction temperature and slow reaction time. Produces Calcium Difluoride and Carbon Dioxide
• Calcium Oxide CaO: Corrosive and causes an extremely high reaction temperature. Produces Calcium Difluoride
• Calcium Hydroxide Ca(OH)2: Easy and safe to store/handle but produces a high reaction temperature. Produces Calcium Difluoride
So which one is the best? That will all depend on where the spilled material is, do you have the capabilities to handle the products produced while neutralizing the spilled material, which materials do you have immediate access to and do you have enough of it to completely neutralize the spilled substance. If we do thorough pre-planning, we can determine the best course of action by knowing where to obtain the neutralizing materials at any given time or have them on-hand.
• Knock it on it’s acid?
But what about initial response considerations? The first in units should begin with a course deluge spray to dilute the material to less than 50% which reduces how much vapor will be released. Generally, a 40:1 ratio of a coarse water spray will knock down the majority of an HF vapor cloud. However, you must consider the initial heat of reaction when using water, but this can be overcome by increasing the amount water which results in better heat absorption by the water. And the run-off could be quite corrosive and methods for confining the runoff must be considered.
• Keep your distance
Protective Action Distances must be considered for Anhydrous HF releases. By referring to the 2016 ERG, we can see that Table 1 of the Green Pages has Small Spill distances as follows:
• Initial Isolation Distance: 30 m or 100 ft
• Small Spill Day: 0.1 km or 0.1 miles
• Small Spill Night: 0.4 km or 0.3 miles
Table 1 does not have Large Spill distances in the 2016 ERG; you must turn to Table 3 for this information. By turning to page 357 of the 2016 ERG; we see UN1052 Hydrogen Fluoride, Anhydrous. Table 3 is broken down into listings for various transport containers and then by wind speeds during day and night. Let’s look at a rail tank car:
• Initial Isolation Distance: 400 m or 1250 ft
• Day – Low Wind: 3.1 km or 1.9 miles
• Day – Moderate Wind: 1.9 km or 1.2 miles
• Day – High Wind: 1.6 km or 1.0 miles
• Night – Low Wind: 6.1 km or 3.8 miles
• Night – Moderate Wind: 2.9 km or 1.8 miles
• Night – High Wind: 1.9 km or 1.2 miles
So the question would be; “Do citizens downwind evacuate or protect in place?” Well, Anhydrous HF and any Aqueous concentrations over 50% will be producing a significant amount of vapors, it is recommended that locations downwind of the spill and within the immediate vicinity protect in place. Air monitoring downwind of the spill can also help determine where the atmospheric concentrations will not be harmful to citizens evacuating.
• Informed decisions make the best decisions.
We have covered quite a bit of material in this article, but if you can take away even just one item from this article that helps you to respond to an HF spill or release, then it was well worth the read. Looking back at our initial scenario of the spill and exposure to a product containing HF, would you feel better responding to that incident now? Information is power, and it helps you to make the correct decisions promptly when dealing with a chemical such as HF.