Explosive Atmospheres, ignition sources and the Fire Risk Assessor

[BLEVE]

BS EN 60079-10-1 contains methods to determine the claasification of hazardous areas due to the release and presence of flammable vapours, mists & gases.

In connection with this standard it is widely accepted that a potentially explosive atmosphere exists around any bolted flange connection located along the length of any particular pipe line (containing flammable liquid, vapour or gas). The extent of this hazrdous area is dependent on the properties of the fluid, size of pipe line/flange and pressure/temperature conditions.

The end result is that all efforts should be made to prevent any one of 14 ignition sources from being present within the hazardous area in  order to prevent ignition, explosion and secondary fires.

This situation is made more difficult as it is apparent that the extent of a hazrdous zone resulting from vapour or gas release under relatively low pressures will be smaller and confined to the vicinity of the source of release, where at greater pressure the extent of the zone will increase and exist at a greater distance fro the source.

Unfortunately, BS EN 60079 does not give consideration to jet release of flammable liquids so again, if we consider a flammeble liquid escaping from the flange scenario we will find that the jet of liquid will travel a distance in any direction (360 degrees) until reaching an obstruction and then begin to form a pool.

The pool will release vapours according to the fluid evaporation rate (depending on temperature and ventilation rate resulting in a defined explosive atmosphere above and beyound the physical boundary of the pool.

Similarly we have the potential for the formation of explosive atmospheres due to dust release or dormant layers of dusts. How do we consider this?

Interestingly or not, the ignition of an explosive atmosphere may seriously affect the general safety precautions and structural integrity of a building structure. Indeed it may also render a number MOE as unusable in a very short period of time.
In this context it is surely important that we give full and honest consideration to Schedule 1 of the RRFSO.

It was my original intention to provide a number of example calculations but i am now aware that this is not appreciated by some as it is considered as being clever.

[Username]

Welcome to the world of the oil industry!

Something I'm not involved with now, but I worked in the North Sea for a number of years.

As well as taking into consideration the extent of a hazardous area (around a flange for example), the other major factor is frequency of release, or failure.

This is where true Fire Engineering comes in with the development of quantatitive risk assessments, hazard and operability studies etc. Subjects which, I hasten to add, are now way beyond my level of competence!

Some good HSE guidance under COMAH here
http://www.hse.gov.uk/comah/sragtech/techmeasareaclas.htm

[CivvyFSO]

If you are looking at any sort of mitigation, selection of intrinsically safe equipment etc, then that is classified by the HSE as measures to cover a process risk. Article 4 of the RRFSO is in place to clearly define the difference between process risks and general fire precautions. This points towards the DSEAR assessment being required as a separate issue to the RRFSO assessment. Owing to that I would suggest that you get the H&S bod to sort his end of the problem out, then the remaining risk should be as low as is reasonably practicable as far as the RRFSO is concerned.

[BLEVE]

But how then do we explain articles 9, 12, 15,16, 19 and Schedule 1.

Again, I cannot see how anyone can complete a fire risk assessment without having sight and a good understanding of a DSEAR RA. Any fire risk assessor must be able to satify themselves that the requirements of the above articles have been demonstrably met and closed out.

[Mike Buckley]

Do we have a chicken and egg situation here? It sounds to me that you cannot do a FRA without having a DSEAR RA, but then can you do a DSEAR RA without a FRA?

The other side (and correct me if I am wrong, (I know you will)) part of DSEAR looks at how likely an explosive atmosphere is to be present. It takes three stages the presence of an explosive atmosphere only rarely, the presence of an explosive atmosphere occaisionally and the presence of an explosive atmosphere virtually continuously.

So if I take the example of an hydraulic press. If one of the high pressure lines splits, it will release a mist of hydraulic oil which will produce a potentially explosive atmosphere. Should all premises, which have hydraulic presses, have a DSEAR risk assessment?

[BLEVE]

Only if the release was foreseeable from a flange or connection (labyrinthine connections typically result in a zone of negligable extent), Hose failure or splitting would be considered as catastrophic and outside the realms of DSEAR.

In connection with the former other factors to be considered are: the flash point of the HO must be within 10 - 15 Kelvin of or above ambient temperature. DSEAR can also apply if process conditions are at or greater than the FP or a hot surface is present at a temperature of or above the fluid auto ignition temperature. Of course if the release is in the form of an aerosol or mist then the FP may be substantially lower that that of the oil in single phase.

Hazardous areas are classed as

Zone 0 Vapour/gas continuously (vapour space of a tank etc)
Zone 1 Vapour/gas present short periods of time during NORMAL operation (Tank vent )
Zone 2 Vapour/gaspresent infrequently for short periods of time during abnormal operation (flange connection, sump, pump gland etc.

Dusts are classed as
Zone 20
Z21
Z22

I cant see any problem with carrying out a DSEAR assessment without or prior to a fire risk assessment but I do not believe that a S&S FRA can be completed without DSEAR input. Just my opinion though,though I do see some larger consultancies taking the same view point.
 

[BLEVE]

It is also interesting to note that a gas fired appliance is outside the remit of DSEAR but would be considered within a FRA.

[BLEVE]

Username,
Ah yes welcome to my daily grind, dont ya just love safety case reports.  

[CivvyFSO]

I cannot see how anyone can complete a fire risk assessment without having sight and a good understanding of a DSEAR RA. Any fire risk assessor must be able to satify themselves that the requirements of the above articles have been demonstrably met and closed out.

I agree with most of that, I think that the level of understanding required is negotiable. If a consultant was doing a RA somewhere and noticed a DSEAR type of risk, and someone like you had done the DSEAR assesssment, I don't think that the ability to do the calcs is necessary for the consultant, but the ability to look at the conclusion of your work and make sense of it would be.

An analogy would be a risk assessor looking at a shopping centre with smoke control. He needs to know it is there, he needs to know what it does. He does not need to sit and do a load of calcs just to ensure that the means of escape is ok.

[BLEVE]

Civvy,
Agreed but the fire risk assessor should be able to recognise that a DSEAR RA should exist or is applicable to a situation and or be able to evaluate any such assessment. In addition he/she should be able to recognise the (if any) impact from the significant findings on the general fire precautions.

To my mind situations where the risk assessor states that "A DSEAR RA" should be carried out as a finding of the fire risk assessment is not S&S as the fire risk assessment would be incomplete as possible impacts from DSEAR have not then been considered. It should be the case that the finding should state that "A DSEAR RA is required and on completion the fire risk assessment should be reviewed so as to consider possible impacts from any significant findings on the general fire precautions) or something along those lines.

However, there is a problem in cases where the RP or his/her employer is not required to record the findings of the DSEAR RA, (maybe the mere existance of a zone is not considered significant in their opinion) or maybe on the advice of a consultant. In these circumstances, it is important that the fire risk assessor is capable of recognising the existance of a potentially explosive atmosphere. If not captured by the fire risk assessor, then the FRA could be considered not to be S&S and liability attached to the fire risk assessor.

[CivvyFSO]

From Guidance Note No. 1

However, those safety measures provided in a workplace in order to prevent or reduce the likelihood of fire arising directly from a work process (including the storage and use of dangerous substances, goods or materials) or to reduce its intensity, will remain within the remit of Health and Safety legislation.
--snip--
In following some of these measures the responsible person will need to consider health and safety regulations and measures regarding work processes and dangerous substances. Close liaison by enforcing authorities with general health and safety enforcing authorities is advisable.
--snip--
Enforcing authorities are reminded that the coverage of the Order, including this article (12), is general fire precautions (as defined) required due to the presence of a dangerous substance. This does not extend to special technical and organisational measures related to the reduction of risk from work processes which are dealt with under health and safety legislation, enforced by the HSE.


Whereas what you are saying makes some sense, I have to consider what can be enforced. I could not enforce the inclusion of DSEAR information in a fire risk assessment. I could enforce the recording of the presence of dangerous substances, persons put at risk by these substances, the measures which have been taken to reduce the risk and the measures which should be taken. However, the measures which should be taken would be pointed out and implemented via DSEAR, and if DSEAR is satisfied, then the RRFSO should be satisfied.

[BLEVE]

Enforcing authorities are reminded that the coverage of the Order, including this article (12), is general fire precautions (as defined) required due to the presence of a dangerous substance. This does not extend to special technical and organisational measures related to the reduction of risk from work processes which are dealt with under health and safety legislation, enforced by the HSE.

While I can see where this is set out within the RRFSO and guidance, I also notice that article 9 (2) and Scedule 1


In aprticular (i) the special, technical and organisational measures and the substances used and their possible interactions;
Article 9(2)


MATTERS TO BE CONSIDERED IN RISK ASSESSMENT IN RESPECT OF DANGEROUS SUBSTANCES

The matters are—


(a) the hazardous properties of the substance;

(b) information on safety provided by the supplier, including information contained in any relevant safety data sheet;

(c) the circumstances of the work including —


(i) the special, technical and organisational measures and the substances used and their possible interactions;

(ii) the amount of the substance involved;

(iii) where the work will involve more than one dangerous substance, the risk presented by such substances in combination; and

(iv) the arrangements for the safe handling, storage and transport of dangerous substances and of waste containing dangerous substances;


(d) activities, such as maintenance, where there is the potential for a high level of risk;

(e) the effect of measures which have been or will be taken pursuant to this Order;

(f) the likelihood that an explosive atmosphere will occur and its persistence;

(g) the likelihood that ignition sources, including electrostatic discharges, will be present and become active and effective;

(h) the scale of the anticipated effects;

(i) any places which are, or can be connected via openings to, places in which explosive atmospheres may occur; and

(j) such additional safety information as the responsible person may need in order to complete the assessment.


Taking the above into account it is difficult to see how the article 12 restriction applies as Schedule 1 is contadictory.

[Tom Sutton]

While I can see where this is set out within the RRFSO and guidance, I also notice that article 9 (2) and Schedule 1

But if you also check out art 4(2) doesn't  that confirm the guidance and  schedule 1 part 1 could be checking up on the HSE and going a little further.

From the consultation document.

We would welcome views as to our proposals to incorporate the provisions of the draft Dangerous Substances Regulations into the proposed Order and to extend the requirement to mitigate the detrimental effects of a fire to all premises covered by the Order.

[CivvyFSO]

So I try to enforce a DSEAR type of assessment as part of a fire risk assessment. RP appeals, referencing guidance note No. 1, which tells us (FRS) to keep our noses out of process risks etc. Who is going to win?

I am not saying that it makes any sense at all, just that there is a distinct dividing line between process/storage risks and general fire precautions. If you were the RP of a chemical company and I started poking my nose in to your process risks etc you would possibly quite rightly tell me to p*ss off. But I can see how, when you pay for a FRA you would not expect the assessor to draw the line at that point.

The guidance suggests that the enforcing authorites may need to work together. I think that this shows that the powers-that-be appreciate that it isn't 100% clear cut.

[BLEVE]

Fair old mess alright