6 replies to this topic

[Chem01]

Hi all,
We are going to install Ammonia gas detectors at different locations of a new NH3 plant. Occupational Exposure limit (OEL) of NH3 is 25 ppm, i.e above 25 ppm people can work in Ammonia environment but for certain limited hours.
I want to know the various limits and safe working hours for that limit, this will help to provide alarm in control room at various concentration to alert the operation personnal. Any reference please....thanks.
Also what should be the maximum range of Ammonia detectors?

[Chem01]

I contacted a nearby Ammonia plant where they've provided detectors to give alarm at 3200 and 5200 ppm, not sure of why this figure has been chosen? Ammonia is fatal above 5000 ppm even for a short exposure.
It apears that plants do not provide detectors to determine safe working hours for the employees rather these are to indicate Ammonia leakage elsewhere.

[latexman]

The reference should be the ammonia supplier's MSDS. The one I googled had 25 ppm TWA, 35 ppm STEL, 50 ppm PEL, and 300 ppm IDLH. I do not understand why the nearby plant would alarm when the concentration approached the lethal dose. By the time their alarm goes off they may have killed some people! The objective is to detect a leak when it is small or early on to warn people and repair it before it gets worse, therefore I'd alarm at the 25 ppm level or below. That's how our ammonia detection system is set-up.

[Qalander (Chem)]

The reference should be the ammonia supplier's MSDS. The one I googled had 25 ppm TWA, 35 ppm STEL, 50 ppm PEL, and 300 ppm IDLH. I do not understand why the nearby plant would alarm when the concentration approached the lethal dose. By the time their alarm goes off they may have killed some people! The objective is to detect a leak when it is small or early on to warn people and repair it before it gets worse, therefore I'd alarm at the 25 ppm level or below. That's how our ammonia detection system is set-up.

Dear Chem01 Hello/Good Morning,
May I suggest to you that, we must visuallize putting ourselves in the situation(s) as it may be our own life at risk.
From this concept& Humanly professional Ethics; the alarming must be at or nearby the TWA value of 25ppm or the max. at PEL value of 50ppm of ammonia to permit 'Safe escape(s) from the scenario by humans like us'
I believe/understand and you should also appreciate this.
Best Regards
Qalander

[Chem01]

Qalender/latexman,
Ammonia gas itself is not a silent killer,,it is toxic however it can be detected when present in small ppm by the personnnel in working area due to irritation it causes when inhaled. In case of heavy leakage it appears in the form of cloud and clearly visible.
On all NH3 plants emergency procedures are available in case of ammonia leakage, operators have face mask all the time to use in case of few ppm Ammonia in area and Full face mask with air cylinders are also available in case of heavy leakage.
This is the reason nearby Ammonia plant have detectors set at very high limits, these detectors are placed near vessels having large Ammonia inside like Ammonia accumulator and chillers.
However i am not aware of any standard reference which specifies alarm limits for ammonia leakage detection,,,further i feel like there is no fool proof mechanism of Amm leakage detection in plant area.
I've seen a NH3 leakage report from ammonia booster pumps (pressure up to 130 kg/cm2) where Ammonia leak jet move towards east and the detector set at 3200 ppm n 5200 ppm was on west side,,it was too late for detectors to sound before that all area operators have shutdown the pumps and whole plant.
Still stuck up............

[latexman]

Chem01,

You have some good points on ammonia, and yes, a fixed detection system will not detect every single leak, but which detection system will detect more leaks, the one with 10 ppm detectors or the one with 3200 ppm detectors? There is no standard for detection limits on ammonia, but repeating a design just because a neighbor plant did it, is not a very good reason by itself. The objective is zero leaks, and the reason we put in detectors is to detect leaks and warn personnel. A system that detects more leaks is inherently better. Once ammonia gets more concentrated than the IDLH (Immediately Dangerous to Life and Health), chances are small a person can save themself once exposed to a continuing leak. They are incapacitated. I cannot be convinced on this, because I have an ammonia detection system that works at low concentrations. We have never gotten a nuisance alarm. Each alarm was traced down to a leak. It is not a burden and I sleep well at night knowing my reasoning has increased the safety and safety culture of the plant.

[Chem01]

Yes latex, it seems right to cover even small leakages if it comes across the detector.
I am going with 0 - 200 ppm.
A heavy ammonia leakage requires a disaster handling plan but then ammonia detector of high
range can alone do nothing, low range serves the purpose.