Last week, David Ayers, Ph.D., CSP, CHMM, and I had a nice chat regarding LOTO and Complex Processes, and one of the areas associated with these LOTOs is the “evacuation” of the HAZMAT within the process/system. We did not have enough time for me to get deep into the weeds on this aspect of isolating a Process/System, so this is my attempt to explain what needs to be done.
1st and most important, evacuating a HAZMAT from a process/system entails a Line/Equipment OPENING (LEO), and this simple fact means this task comes with some serious risks. Most of the facilities I worked at required this evacuation to be done under a LEO Permit. This permitting process aids in managing the risks, but there are other factors to consider.
2nd – What is the HAZMAT, and what state is it in, and will it stay in that state when it is evacuated? I do a lot of work in NH3 and Cl2 processes so I will use these chemicals in my example. These chemicals are NORMALLY a GAS, but in most processes they are Liquids Under Pressure. This means we want to use a VENT VALVE vs. a DRAIN VALVE. A vent valve comes off the top of the piping, and a drain valve will come off the bottom. Using a drain valve means we can send these chemicals in their liquid state to our “destruction/absorption device”, usually a drum or tote of water. Both NH3 and CL2 have boiling points of -28F and -29F, which means when they come in contact with warm water, they begin to boil rapidly, changing to a gas, which expands 850:1 for NH3 and 450:1 for Cl2. In other words, we can blow up our drum or tote! So BE SURE to always use the VENT valve!
3rd – Hoses are NOT created equally! We must use a hose that is DESIGNED and PROVEN for the chemicals and pressures it will see in this task. We need the hose to be ONLY as long as necessary. The longer the hose, the greater the risk, as the hose is usually the weak link in our chain. The hose needs to be long enough to reach the bottom of our secondary container, so the GAS bubbles up through the water (i.e., thescrubber). Using a “sparger” is a great addition.
4th – KNOW how much “liquid/Gas” needs to be evacuated, as this will dictate the amount of water (or other scrubbing solution). For example, for every pound of NH3 we need at least 1 gallon of water. If we are working with Cl2, we need 2 gallons of water for every pound of Cl2. In today’s world of AI, we can simply ask AI, “How many pounds of NH3/Cl2 are in a schedule 40, 2″ liquid pipe that is 125′ in length?” BTW, the 125′ is the fictitious distance between the two (2) isolation valves we closed and locked in our example.
5th – A dead-man valve (a Spring-Loaded Fail-Safe CLOSED valve) is a MUST-have for these evacuations. We want the valve placed at the end of the hose attached to the vent line on the piping. This PASSIVE ENGINEERING CONTROL is critical should something happen and we have an UNCONTROLLED RELEASE during the evacuation between the Dead-Man valve and our “srubber”. The operator only needs to let go, and the valve closes, and they walk away.
NOTE: PLEASE do not take the position that we can release these Highly Hazardous Chemicals/Extremely Hazardous Substances into the atmosphere as long as we stay below the chemical’s RQ. This is NOT a compliance game, and the idea of telling the workforce that we can deliberately release the HHC/EHS to the atmosphere simply because we are under the government’s limit will undermine respect for these HHC/EHSs, and this will come back to bite us!
6th – Although we are somewhat controlling this release into a “scrubber”, PPE plays a major role in worker protection in such a high-risk task. For NH3 and Cl2, we ALWAYS did this task in supplied air with EEBAs or using SCBAs. This level of RP is chosen due to the LOW IDLHs of these chemicals. We may use a lower CPC for our torso protection, as we are primarily concerned with inhalation hazards, but we always classify our PPE as LEVEL B.
7th – ALWAYS work with the environmental team on handling the contaminated water. This water will be at a very high pH, and in terms of NH3, we will have made Ammonium Hydroxide (NH4OH). These solutions will most likely be managed as a HAZWASTE. But for sure, we will need to have this drum(s) tand tote(s) properly labeled to convey the hazards of the solution. (1910.1200(f)(6)
This should give everyone something to think about. We will go deeper into these items and discuss flammable liquids and flammable gases in the next article.