Safety Overview

Identification of hazardous substances based on physical quantities

As has been shown, a classification of different hazardous substances according to their chemical structure, although in principle possible, but not always clear. 
A classification according to their physico-chemical properties and the resulting hazards is much more useful here. 
In the following, the most important key figures in connection with physical hazards are presented. They are the prerequisite for being able to classify the various types of risk in the next step.

General chemical-physical parameters

In order to characterize chemical substances, compounds or even mixtures, their chemical-physical parameters can be used in addition to their chemical composition. This includes:
Boiling point T sd = f (p) Density = f (p, T) Particle size distribution
Vapor pressure p D = f (T) Viscosity = f (p, T, ρ) of formation
Melting point T Sm = f (p) PH value Solubility in water or fat

In addition to these general parameters, it is also possible to determine specific safety-related key figures for the assessment of the hazards of these substances. These are used to describe the physico-chemical behavior of substances in order to assess their potential explosion hazards. In the rarest cases, the key figures are pure substance constants.

The individual safety parameters have grown historically, which means that the measurement specifications are sometimes not practical and meaningful. 
In addition, the key figures also depend on the respective measurement method. For the comparability of the key figures, they are determined using standardized measuring methods. The tests to determine the metrics are optimized so that the metrics that describe a substance’s ability to ignite assume minimums, and the metrics that describe the effects of explosions assume maximums. It has to be accepted as a binding convention by which an expert in this field can give an assessment of explosion hazards in a given situation.

Safety characteristics of combustible gases and liquids

The handling of flammable gases and vapors must be given special attention from a safety point of view. The temperatures occurring in an explosive reaction can reach 1000 ° C and more. The pressure reaches on average about 8 to 10 times the value of the outlet pressure.

Not all key figures need to be determined for the individual protection principles available. The following table lists the most important parameters to be observed depending on the desired protection concept.

In detail, the individual parameters are to be defined and the measuring methods presented. At the same time, the dependency on the temperature, pressure and concentration should be considered.

protection concept defense   Characteristic to be observed
Primary Avoidance or limitation of substances that can form an explosive atmosphere    
Measures which prevent or limit the formation of hazardous explosive atmospheres (avoid explosive atmospheres) concentration limit Explosion limits or lower and upper explosion point, flash point
inerting Limiting oxygen concentration
Secondary Measures that prevent the ignition of hazardous explosive atmospheres   Minimum ignition energy, ignition temperature, exothermic decomposition, electrostatic behavior
Tertiary Constructional measures that limit the effect of an explosion to an acceptable level (constructive explosion protection) Explosion-resistant construction Maximum explosion overpressure
Explosion pressure shock resistant design (explosion pressure relief) G value, maximum explosion overpressure
Explosion pressure shock resistant design (explosion suppression) G value, maximum explosion overpressure

Safety characteristics of dusts

The handling of substances that are powdery or dusty is an activity that has been known for over two hundred years to require careful safety assessment and assessment to avoid serious accidents.
Drying, milling, sieving, mixing and granulating are examples of such basic operations associated with the handling of powders and dusts.
In the following, the peculiarities of the safety-related key data of dusts will be discussed. It should be distinguished between the

  • Fire properties of deposited dusts
  • Explosive properties of fluidized dusts
  • Some safety-related key figures for dusts are similar to those for flammable liquids and gases, although a modified measuring method must be used for dusts.

 

The following diagram illustrates the basic procedure for the systematic determination of the key figures required for dusts.

Not all key figures need to be determined for the individual protection principles available. In the following table, depending on the desired protection concept, the respective parameter to be observed is listed:

protection concept defense   Characteristic to be observed
Primary Avoidance or limitation of substances that can form an explosive atmosphere Flammability / burning number explosiveness
Measures which prevent or limit the formation of hazardous explosive atmospheres (avoid explosive atmospheres) concentration limit explosion limits
inerting Limiting oxygen concentration
Secondary Measures that prevent the ignition of hazardous explosive atmospheres Minimum ignition Ignition ignition temperature Auto-ignition behavior exothermic decomposition electrostatic behavior impact sensitivity smoldering
Tertiary Constructional measures that limit the effect of an explosion to an acceptable level (constructive explosion protection) Explosion-resistant construction Maximum explosion overpressure
Explosion pressure shock resistant design (explosion pressure relief) St value maximum explosion overpressure
Explosion pressure shock resistant design (explosion suppression) St value maximum explosion overpressure