Time Weighted Average Calculation
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- čas přidán 27. 07. 2024
- The time weighted average TWA) is a measure of a worker's average exposure to a contaminant, over the length of a work shift. The OSHA permissible exposure limit (PEL) is a TWA, as is the TLV recommendations from the ACGIH. Modern sampling instruments will calculate the TWA but it is still important to understand the concept and do the calculations. The tutorial also includes information about adjusting the PEL (or other exposure limit) for work shifts exceeding eight hours. Material is from SAFM 3423 and SAFM 4423 Northeastern State University. The EHSM program at Northeastern has been identified as a Qualified Academic Program by the Board of Certified Safety Professionals. The presenter is Dr. Doug Martin. Dr. Martin earned his Ph.D. from Oklahoma State University and is a CSP. In addition Dr. Martin worked as a safety manager in the construction industry for 20 years. For more information about the EHSM program at Northeastern you may contact Dr. Martin at marti223@nsuok.edu.
One of the best explanations of OEL's. Thanks, much appreciated 🌄
thanks for the video. this is the best explanation i have have seen on this topic.
Great Explanation of TWA and PEL calculation. Thanks for sharing such valuable knowledge👍🙏
Thank you for the kind words. I appreciate it.
Thanks so much. As a residential HVAC contractor we perform C.O. monitoring from our customer's gas furnace. Sometimes folks have a cracked heat exchanger where the spent gasses could escape into the air ducts and on into the room.
So the 8hr TLV/PEL for CO is 50ppm (per OSHA). That's 400 ppm over any 1 hour period, 50ppm for 8hrs, 17.5 for 14 hours (average time spent at home), 2ppm for 22 hours (stay at home parents/retirees/unemployed), and 0 ppm for 24 hours a day (bed-ridden).
The examples were great. I feel much better about telling my techs how to advise our customers on any readings we get - and please feel free to comment/correct me if I'm wrong. Thanks again. This is the best and clearest explanation.
CO is an often overlooked airborne hazard. There are way too many preventable deaths each year. I would not be comfortable with 400 ppm exposure for a one hour period. If you send me an email address I’ll send you a chart showing health effects at different exposure levels. In a home environment I would recommend diagnosing the problem and taking corrective action when detected at 10 ppm or greater.
Let me qualify my previous comment, 10 ppm and greater concentrations detected in living areas should be diagnosed (identify source) and corrective actions taken. Furnace rooms, hot water heater areas, garages (unless occupied) etc. would be exceptions.
Thanks for clearing my doubts i cant wait to SUBSCRIBE to your channel
Amazing command and good explanation. Keep uploading ✌️
Thank you. I have about 100 more I'll be uploading over the next couple of years.
Thank you!
Welcome!
Liked and subscribed
Thank you.
Thanks for uploading this lesson!! I just finished an introductory Industrial Hygiene course. I had hoped for it to be a little more advanced. I was disappointed when I discovered the course was not going to provide any lessons in using the TWA formulas.
By using the examples, your video brings the math to life and I can clearly see that it really is as easy as you said it was. I believe that taking the time to understand this math is what sets the real safety professionals apart from the entry level.
For discussion - for respirable dusts, how would we know what the exposure rates per hour are? Would that be a matter of changing out the collection cassettes each hour to get that hourly measurement?
An industrial hygiene class that did not cover Time Weighted Average!! You should ask for a refund--LOL. Glad the video helps.
Monitoring for respirable dusts requires the use of different instruments, depending on the dust of interest. Silica for example we use a personal sampling pump connected to a cyclone. The pump draws air through the cyclone (usually at 1.7 liters per minute) and microscopic particles are captured on filter media. Filter media is then sent to a lab and processed. The lab tech basically counts the number of particles. The number of particles along with the sampling time will provide a measure of exposure. This is a three lecture question. Hope the brief answer helps.
Please tell how the formula for reduction factor is derived ?
Good day
How do I calculate STEL in excel showing in a graph.
Thank you so much.
Thx bro. I have exam tomorrow and I didn't know what to do
Good luck.
We have the DPM survey of value TWA(4hrs) is 203microgram/m3. Working hours was 8hrs & PEL as per 8hrs TWA was 100microgram/m3. So what will be the value of 8hrs TWA?
Thanks for uploading such a detailed video, it really helped. just one Question - will PEL be mentioned in safety data sheet or we have to search through HSE alike bodies? like for silica its 50
PEL, the OSHA permissible exposure limit will normally be found in the SDS. However, depending on the product, there may be multiple harmful constituents and the PEL for each constituent will be reported.
@@SafetyProCalculations i have an exam question and dont know how to convert 2 litre sodium hydroxide solution into mg/m3. any help please
@@decentmwt1 Sorry. Can't help you on an exam. Contact your professor.
Please tell how the formula for reduction factors is derived ?
It is from a recommendation made in 2003 by the American Conference of Governmental Industrial Hygienists (ACGIH). Beyond that I did not know it's history. In the U.S. it is a recommended method and is not required by any governmental authority. Hope this helps.
What if it was a 12 hour work day, but an employee was only performing abatement for 85 minutes of the day?
There are adjustments (correction factor) for workdays exceeding 8 hours. Should be covered in the video. Also for some substance there are published exposure limits for 10 hr workdays. Record zero exposure for part of the workday not involved in abatement activities. If abatement involves lead or asbestos I encourage you to review OSHA guidance for exposure to those substances.
Do you have a video on exposure mixture?
These may help you.
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czcams.com/video/LNo7ekLEQyI/video.html
Sent you the same link twice. Here is the other video that might be what you're looking for.
czcams.com/video/1XmzaATcK8s/video.html
Silly question, what does the 'n' represent in the formula ? ie Cn Tn ??
Not silly. In a work day there could be three, four, five, or more concentration periods. The n is just mathematical notation telling us to included all the concentration periods. Does this make sense to you?
@@SafetyProCalculations
Yes, thank you for the explanation.