One of the safety seminars I teach is on the general topic of reactive hazards. There is a bit of a challenge to this because the idea is to cultivate informed caution rather than allow broadband fear to rule. It is challenging because my class is generally populated with non-chemist plant operators or other support staff. Out in the world the word “chemical” is generally taken to be an epithet and indicative of some malign influence. We who work with chemicals are in a position to bear witness to the reality of chemistry in our lives and to speak calmly and reasonably about it, without crass cheerleading.

Here is how I look at this. There are hazards and there are dangers. A hazard is something that can cause harm if it was to be fully expressed by way of physical contact with people or certain objects, unbounded access to an ignition source, exposure to air, etc. A critical feature of the hazard definition is that there are layers of protection preventing undesired contact. Hazards can be contained. A contained hazard is safer to be around than an uncontained hazard.

An uncontained hazard is that which can cause harm without the interference of effective layers of protection. A hungry tiger in a cage is hazardous in that there is the potential for trouble if the cage is breached. Being openly exposed to that tiger is what I’ll call dangerous.

Likewise, a stable chemical in a bottle has a physical layer of protection around it. A policy on the use of that bottled chemical constitutes a concentric administrative layer of protection. The bottle sitting in a proper cabinet within a room with limited access has more layers of protection. The policy of selling that chemical only to qualified buyers is a further layer of protection.

Egg white to which has been added several drops of conc H2SO4 (bottom) and 50 % caustic (top). Two minutes have elapsed. The point of this demo is to show what might happed to a cornea on contact with these reagents. The clouding is irreversible. People remember demonstrations.

It is possible to work around contained hazards safely and most of us do this outside of work without giving it much thought. Hazardous energy is exploited by most of us in the form of moving automobiles, spinning jet turbines, rotating machinery of all kinds, compressed gases and springs, and flammable liquids. Safe operation around these hazards is crucial to the conduct of civilization right down to our daily lives.

It is very easy for experts to frighten the daylights out of people by an unfortunate choice of words or simply dwelling on the hazardous downside too much. Users of technology should always be versed in the good and bad elements as a matter of course.

Risk can be defined as probability times consequence. So, to reduce risk one can reduce probability, diminish undesired consequences, or both.  This is the purpose of LOPA, or Layers of Protection Analysis. LOPA can provide a quantitative basis for safety policy. The video below will explain.

https://youtu.be/L3kQ9DKHS5A

Designing for tolerable risk is something that all of us in industry must come to grips with.