July 29, 2014

HACCP Principle 3: Establish Critical Limits

Written by Dave Ruede | Food Safety, HACCP

Hazards and Critical Control Points are identified, but how much control is needed?


I’m not sure if it’s urban legend or not, but I have been told that manufacturers of modern cars equipped with computers have the ability to limit the top speed of their products. A friend’s son stationed in Germany had a Camaro sent over and was looking for a computer chip that could override the top speed limit for his Autobahn stints, not sure if he was successful but he’s still alive so maybe not. For most of us car top speed limiters are not a concern as driving much more than 70 mph or 75 mph in today’s crowded and well policed US highways is rare. Just this weekend a driver on the highway I was traveling decided that traffic was not going fast enough and was passing everyone at speeds well above the speed limit, and most drivers were already above the speed limit already. Where there’s safety in numbers, the speeding driver was singled out by the local constabulary (a.k.a. state police trooper) for special attention. Needless to say all those around me arrived a their destinations on schedule and with all of our funds and insurance rating preserved.


Drivers moving too slow can also be a hazard and some highways are posted with minimum speeds. As I did when traffic was flowing freely, using cruise control can help insure that drivers do not go too fast or two slow, keeping the vehicle within the critical limits.


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I like the definition of Critical Limit offered by Cornell University: Critical Limit: A maximum and/or minimum value to which a biological, chemical or physical parameter must be controlled at a CCP to prevent, eliminate or reduce to an acceptable level the occurrence of a food-safety hazard. It reminds us that biological, chemical, and physical hazards are all important and not to focus on one or two, those we’re most familiar or comfortable with. It also reminds us that while eliminating a hazard may be preferred it may not be achievable, therefore reducing them to acceptable levels is necessary. Again the science is important: what are the FDA or other reputable sources defining as acceptable limits.


Establishing critical limits for food products is in some ways like establishing speed limits. The HACCP Team’s challenge is to apply Critical Limits to the Critical Control Points (CCPs) that promote safety and are balance with scientific evidence and the business’ capabilities. For example, if the hazard analysis determines that worker hands need to be washed before handling food products, the control point is the hand washing station prior to the food handling. But how clean is clean, how much and what type of hand washing is needed? Do workers need to wash as well as surgeons entering a sterile operating room? In many hospitals the length and type of hand washing is prescribed, as a link to the US NIH website describing WHO handwashing procedures before surgery demonstrates (Link to Source).


4. Types of hand care    
Type Purpose Method
Hand wash Remove soil and transient microorganisms Soap or detergent and friction for at least 10-15 seconds
Hand antisepsis Remove and/or destroy transient and resident microorganisms to control infection transfer from hands Antimicrobial soap or detergent or alcohol-based hand-rub and friction for at least 10-15 seconds
Surgical hand scrub Remove or destroy transient and resident microoganisms to control/prevent infection in patients undergoing operations Antimicrobial soap or detergent preparation with brush to achieve friction for at least 120 seconds, or alcohol-based preparation for at least 20 seconds

Table of handwashing types, purposes and methods for food service workers.


HACCP Team members will need to research the level of handwashing needed to prevent the spread of microorganisms in order to set Critical Limits for microorganisms of concern for their particular products, for example dairy and seafood may require higher levels of sanitization depending on the products. Here the science is very important. The science need not include laboratory testing of workers hands to determine how well they comply with procedures. It will likely include a search of best practices for a particular operation. And if environmental factors other than those that determine best practices exist, they will need to be taken into account when limits are set.


Of course worker hand cleanliness is important but not the only potential hazard. Critical Limits are set to insure that all identified biological, physical, or chemical hazards are addressed, each CCP will have at least one Critical Limit. In many cases the Critical Limit is set by regulations or scientific data.


The University of Florida offers some questions the HACCP Team may consider.

  • How are Control Limits identified?
  • What are the appropriate and reasonable parameters or boundaries for food safety?
  • What is the method that will be applied to determine the magnitude of each parameter?
  • What are the measurable criteria?


Here are some examples of parameters that are measurable and can be used to set critical limits.

  • Time: Cooking time, rate, time at temperature, etc.
  • Temperature: Ideal, maximum, minimum.
  • pH: Acidity of a liquid
  • Water Activity: Vapor pressure of water at a particular temperature
  • Moisture: Amount of moisture in food
  • Titratable (means of measuring) acidity: Total acidity determined by chemical analysis


Turning again to the source of the Critical Limit definition (Link to Source), here are some examples of critical limits in one food industry: seafood. Table 1 provides examples of biological hazards and methods of control along with critical limits for each.


Table 2 identifies sources for the critical limits, in many cases regulatory agency or scientific publications by reputable sources in the industry. Note in-house experiments are included along with laboratory support. This is important because critical limits are method dependent, they can be modified and still achieve the desired result as long as the results are scientifically validated and verified. For example, adjusting cooking temperature and time or moisture levels to achieve a more desirable product is acceptable if the result eliminate or reduce levels of microorganisms of concern to safe levels. Cooking is an art but safety needs to be validated and verified by science when consumer safety is at stake.


Table 4 demonstrates a more complete definition of a critical limit, defining cooking temperature and time as well as the minimum internal temperature and time to meet the critical limit.Cooking foods that have a high chance of containing harmful microorganisms (e.g. seafood) will require a fuller definition of what is needed for the critical limit.


The types of food products, hazards and processing methods will determine what is needed to achieve the Critical Limits. Many food industry operations have a good record of food safety, identifying current methods and parameters is a good place to start. The HACCP team can begin to document what has worked, whether or not the identified CCPs exist and from there establish Critical Limits. Again worker buy-in is critical, acknowledging the good work currently being done is a way to start to achieve the total HACCP plan.


Topics: Food Safety HACCP

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